args.hxx

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/* A simple header-only C++ argument parser library.
 *
 * https://github.com/Taywee/args
 *
 * Copyright (c) 2016-2024 Taylor Richberger <taylor@axfive.net> and Pavel
 * Belikov
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */
 
#ifndef ARGS_HXX
#define ARGS_HXX
#pragma push_macro("min")
#pragma push_macro("max")
#undef min
#undef max
 
#define ARGS_VERSION "6.6.1"
#define ARGS_VERSION_MAJOR 6
#define ARGS_VERSION_MINOR 6
#define ARGS_VERSION_PATCH 1
 
#include <algorithm>
#include <iterator>
#include <exception>
#include <functional>
#include <sstream>
#include <string>
#include <tuple>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <type_traits>
#include <cstddef>
#include <cctype>
#include <cerrno>
#include <cstdlib>
#include <limits>
#include <iostream>
 
#if defined(_MSC_VER) && _MSC_VER <= 1800
#define noexcept
#endif
 
namespace args
{
    template <typename Option>
    auto get(Option &option_) -> decltype(option_.Get())
    {
        return option_.Get();
    }
 
    inline std::string::size_type Glyphs(const std::string &string_)
    {
        std::string::size_type length = 0;
        for (const char c: string_)
        {
            if ((c & 0xc0) != 0x80)
            {
                ++length;
            }
        }
        return length;
    }
 
    template<typename T>
    bool SafeAdd(T a, T b, T& out) noexcept
    {
        static_assert(std::is_integral<T>::value, "SafeAdd requires integral types.");
        if (std::is_unsigned<T>::value)
        {
            using U = typename std::make_unsigned<T>::type;
            const U ua = static_cast<U>(a);
            const U ub = static_cast<U>(b);
            const U maxv = std::numeric_limits<U>::max();
            if (ua > maxv - ub)
            {
                return false;
            }
            out = static_cast<T>(ua + ub);
            return true;
        }
        else
        {
#if defined(__clang__) || defined(__GNUC__)
            return !__builtin_add_overflow(a, b, &out);
#else
            // Fallback bounds check
            if (b > 0 && a > std::numeric_limits<T>::max() - b)
            {
                return false;
            }
            if (b < 0 && a < std::numeric_limits<T>::min() - b)
            {
                return false;
            }
            out = a + b;
            return true;
#endif
        }
    }
 
    template<typename T>
    bool SafeMultiply(T a, T b, T& out) noexcept
    {
        static_assert(std::is_integral<T>::value, "SafeMultiply requires integral types.");
 
        if (a == 0 || b == 0)
        {
            out = 0;
            return true;
        }
 
        if (std::is_unsigned<T>::value)
        {
            using U = typename std::make_unsigned<T>::type;
            const U ua = static_cast<U>(a);
            const U ub = static_cast<U>(b);
            const U maxv = std::numeric_limits<U>::max();
            if (ub > maxv / ua)
            {
                return false;
            }
            out = static_cast<T>(ua * ub);
            return true;
        }
        else
        {
#if defined(__clang__) || defined(__GNUC__)
            return !__builtin_mul_overflow(a, b, &out);
#else
            // Fallback bounds check
            if (a == -1 && b == std::numeric_limits<T>::min())
            {
                return false;
            }
            if (b == -1 && a == std::numeric_limits<T>::min())
            {
                return false;
            }
            if ((a > 0 && b > 0 && a > std::numeric_limits<T>::max() / b) ||
                (a > 0 && b < 0 && b < std::numeric_limits<T>::min() / a) ||
                (a < 0 && b > 0 && a < std::numeric_limits<T>::min() / b) ||
                (a < 0 && b < 0 && a < std::numeric_limits<T>::max() / b))
            {
                return false;
            }
            out = a * b;
            return true;
#endif
        }
    }
 
    template<typename T>
    bool SafeSub(T a, T b, T& out) noexcept
    {
        static_assert(std::is_integral<T>::value, "SafeSub requires integral types.");
        if (std::is_unsigned<T>::value)
        {
            if (a < b)
            {
                return false;
            }
            out = a - b;
            return true;
        }
        else
        {
#if defined(__clang__) || defined(__GNUC__)
            return !__builtin_sub_overflow(a, b, &out);
#else
            // Fallback bounds check
            if (b > 0 && a < std::numeric_limits<T>::min() + b)
            {
                return false;
            }
            if (b < 0 && a > std::numeric_limits<T>::max() + b)
            {
                return false;
            }
            out = a - b;
            return true;
#endif
        }
    }
 
    // Unsigned overload
    template<typename T>
    typename std::enable_if<std::is_unsigned<T>::value, bool>::type
    SafeNeg(T a, T& out) noexcept
    {
        static_assert(std::is_integral<T>::value, "SafeNeg requires integral types.");
        if (a != 0)
        {
            return false;
        }
        out = 0;
        return true;
    }
 
    // Signed overload
    template<typename T>
    typename std::enable_if<std::is_signed<T>::value, bool>::type
    SafeNeg(T a, T& out) noexcept
    {
        static_assert(std::is_integral<T>::value, "SafeNeg requires integral types.");
        if (a == std::numeric_limits<T>::min())
        {
            return false;
        }
        out = -a;
        return true;
    }
 
    template <typename It>
    inline std::vector<std::string> Wrap(It begin,
                                         It end,
                                         const std::string::size_type width,
                                         std::string::size_type firstlinewidth = 0,
                                         std::string::size_type firstlineindent = 0)
    {
        std::vector<std::string> output;
        std::string line(firstlineindent, ' ');
        bool empty = true;
 
        if (firstlinewidth == 0)
        {
            firstlinewidth = width;
        }
 
        auto currentwidth = firstlinewidth;
 
        for (auto it = begin; it != end; ++it)
        {
            if (it->empty())
            {
                continue;
            }
 
            if (*it == "\n")
            {
                if (!empty)
                {
                    output.push_back(line);
                    line.clear();
                    empty = true;
                    currentwidth = width;
                }
 
                continue;
            }
 
            auto itemsize = Glyphs(*it);
            
            // Refactored to prevent integer overflow
            bool needsWrap = false;
            if (itemsize >= currentwidth)
            {
                needsWrap = true;
            }
            else
            {
                size_t remainingWidth = (currentwidth > itemsize) ? (currentwidth - itemsize) : 0;
                size_t nextLength = 0;
                if (!SafeAdd<std::string::size_type>(line.length(), static_cast<std::string::size_type>(1), nextLength) || nextLength > remainingWidth)
                {
                    needsWrap = true;
                }
            }
            
            if (needsWrap)
            {
                if (!empty)
                {
                    output.push_back(line);
                    line.clear();
                    empty = true;
                    currentwidth = width;
                }
            }
 
            if (itemsize > 0)
            {
                if (!empty)
                {
                    line += ' ';
                }
 
                line += *it;
                empty = false;
            }
        }
 
        if (!empty)
        {
            output.push_back(line);
        }
 
        return output;
    }
 
    namespace detail
    {
        template <typename T>
        std::string Join(const T& array, const std::string &delimiter)
        {
            std::string res;
            
            // Safely compute reservation size to avoid unbounded reallocations
            using size_type = std::string::size_type;
            size_type total = 0;
            size_type count = 0;
            const size_type delim_size = static_cast<size_type>(delimiter.size());
            bool can_reserve = true;
            
            for (const auto &element : array)
            {
                const size_type elem_size = static_cast<size_type>(element.size());
                if (!SafeAdd<size_type>(total, elem_size, total))
                {
                    can_reserve = false;
                    break;
                }
                ++count;
            }
            
            if (can_reserve && count > 1)
            {
                size_type delim_count = count - 1;
                size_type delim_total = 0;
                if (!SafeMultiply<size_type>(delim_count, delim_size, delim_total) ||
                    !SafeAdd<size_type>(total, delim_total, total))
                {
                    can_reserve = false;
                }
            }
            
            if (can_reserve && total > 0)
            {
                res.reserve(total);
            }
            
            bool first = true;
            for (const auto &element : array)
            {
                if (!first)
                {
                    res += delimiter;
                }
                res += element;
                first = false;
            }
            
            return res;
        }
    }
 
    inline std::vector<std::string> Wrap(const std::string &in, const std::string::size_type width, std::string::size_type firstlinewidth = 0)
    {
        // Preserve existing line breaks
        const auto newlineloc = in.find('\n');
        if (newlineloc != in.npos)
        {
            auto first = Wrap(std::string(in, 0, newlineloc), width);
            auto second = Wrap(std::string(in, newlineloc + 1), width);
            first.insert(
                std::end(first),
                std::make_move_iterator(std::begin(second)),
                std::make_move_iterator(std::end(second)));
            return first;
        }
 
        std::istringstream stream(in);
        std::string::size_type indent = 0;
 
        for (auto c : in)
        {
            if (!std::isspace(static_cast<unsigned char>(c)))
            {
                break;
            }
            ++indent;
        }
 
        return Wrap(std::istream_iterator<std::string>(stream), std::istream_iterator<std::string>(),
                    width, firstlinewidth, indent);
    }
 
#ifdef ARGS_NOEXCEPT
    enum class Error
    {
        None,
        Usage,
        Parse,
        Validation,
        Required,
        Map,
        Extra,
        Help,
        Subparser,
        Completion,
    };
#else
    class Error : public std::runtime_error
    {
        public:
            Error(const std::string &problem) : std::runtime_error(problem) {}
            virtual ~Error() {}
    };
 
    class UsageError : public Error
    {
        public:
            UsageError(const std::string &problem) : Error(problem) {}
            virtual ~UsageError() {}
    };
 
    class ParseError : public Error
    {
        public:
            ParseError(const std::string &problem) : Error(problem) {}
            virtual ~ParseError() {}
    };
 
    class ValidationError : public Error
    {
        public:
            ValidationError(const std::string &problem) : Error(problem) {}
            virtual ~ValidationError() {}
    };
 
    class RequiredError : public ValidationError
    {
        public:
            RequiredError(const std::string &problem) : ValidationError(problem) {}
            virtual ~RequiredError() {}
    };
 
    class MapError : public ParseError
    {
        public:
            MapError(const std::string &problem) : ParseError(problem) {}
            virtual ~MapError() {}
    };
 
    class ExtraError : public ParseError
    {
        public:
            ExtraError(const std::string &problem) : ParseError(problem) {}
            virtual ~ExtraError() {}
    };
 
    class Help : public Error
    {
        public:
            Help(const std::string &flag) : Error(flag) {}
            virtual ~Help() {}
    };
 
    class SubparserError : public Error
    {
        public:
            SubparserError() : Error("") {}
            virtual ~SubparserError() {}
    };
 
    class Completion : public Error
    {
        public:
            Completion(const std::string &flag) : Error(flag) {}
            virtual ~Completion() {}
    };
#endif
 
    struct EitherFlag
    {
        const bool isShort;
        const char shortFlag;
        const std::string longFlag;
        EitherFlag(const std::string &flag) : isShort(false), shortFlag(), longFlag(flag) {}
        EitherFlag(const char *flag) : isShort(false), shortFlag(), longFlag(flag) {}
        EitherFlag(const char flag) : isShort(true), shortFlag(flag), longFlag() {}
 
        static std::unordered_set<std::string> GetLong(std::initializer_list<EitherFlag> flags)
        {
            std::unordered_set<std::string>  longFlags;
            for (const EitherFlag &flag: flags)
            {
                if (!flag.isShort)
                {
                    longFlags.insert(flag.longFlag);
                }
            }
            return longFlags;
        }
 
        static std::unordered_set<char> GetShort(std::initializer_list<EitherFlag> flags)
        {
            std::unordered_set<char>  shortFlags;
            for (const EitherFlag &flag: flags)
            {
                if (flag.isShort)
                {
                    shortFlags.insert(flag.shortFlag);
                }
            }
            return shortFlags;
        }
 
        std::string str() const
        {
            return isShort ? std::string(1, shortFlag) : longFlag;
        }
 
        std::string str(const std::string &shortPrefix, const std::string &longPrefix) const
        {
            return isShort ? shortPrefix + std::string(1, shortFlag) : longPrefix + longFlag;
        }
    };
 
 
 
    class Matcher
    {
        private:
            const std::unordered_set<char> shortFlags;
            const std::unordered_set<std::string> longFlags;
 
        public:
            template <typename ShortIt, typename LongIt>
            Matcher(ShortIt shortFlagsStart, ShortIt shortFlagsEnd, LongIt longFlagsStart, LongIt longFlagsEnd) :
                shortFlags(shortFlagsStart, shortFlagsEnd),
                longFlags(longFlagsStart, longFlagsEnd)
            {
                if (shortFlags.empty() && longFlags.empty())
                {
#ifndef ARGS_NOEXCEPT
                    throw UsageError("empty Matcher");
#endif
                }
            }
 
#ifdef ARGS_NOEXCEPT
            Error GetError() const noexcept
            {
                return shortFlags.empty() && longFlags.empty() ? Error::Usage : Error::None;
            }
#endif
 
            template <typename Short, typename Long>
            Matcher(Short &&shortIn, Long &&longIn) :
                Matcher(std::begin(shortIn), std::end(shortIn), std::begin(longIn), std::end(longIn))
            {}
 
            Matcher(std::initializer_list<EitherFlag> in) :
                Matcher(EitherFlag::GetShort(in), EitherFlag::GetLong(in)) {}
 
            Matcher(Matcher &&other) noexcept : shortFlags(std::move(other.shortFlags)), longFlags(std::move(other.longFlags))
            {}
 
            ~Matcher() {}
 
            bool Match(const char flag) const
            {
                return shortFlags.find(flag) != shortFlags.end();
            }
 
            bool Match(const std::string &flag) const
            {
                return longFlags.find(flag) != longFlags.end();
            }
 
            bool Match(const EitherFlag &flag) const
            {
                return flag.isShort ? Match(flag.shortFlag) : Match(flag.longFlag);
            }
 
            std::vector<EitherFlag> GetFlagStrings() const
            {
                std::vector<EitherFlag> flagStrings;
                flagStrings.reserve(shortFlags.size() + longFlags.size());
                for (const char flag: shortFlags)
                {
                    flagStrings.emplace_back(flag);
                }
                for (const std::string &flag: longFlags)
                {
                    flagStrings.emplace_back(flag);
                }
                return flagStrings;
            }
 
            EitherFlag GetLongOrAny() const
            {
                if (!longFlags.empty())
                {
                    return *longFlags.begin();
                }
 
                if (!shortFlags.empty())
                {
                    return *shortFlags.begin();
                }
 
                // should be unreachable
                return ' ';
            }
 
            EitherFlag GetShortOrAny() const
            {
                if (!shortFlags.empty())
                {
                    return *shortFlags.begin();
                }
 
                if (!longFlags.empty())
                {
                    return *longFlags.begin();
                }
 
                // should be unreachable
                return ' ';
            }
    };
 
    enum class Options
    {
        None = 0x0,
 
        Single = 0x01,
 
        Required = 0x02,
 
        HiddenFromUsage = 0x04,
 
        HiddenFromDescription = 0x08,
 
        Global = 0x10,
 
        KickOut = 0x20,
 
        HiddenFromCompletion = 0x40,
 
        Hidden = HiddenFromUsage | HiddenFromDescription | HiddenFromCompletion,
    };
 
    inline Options operator | (Options lhs, Options rhs)
    {
        return static_cast<Options>(static_cast<int>(lhs) | static_cast<int>(rhs));
    }
 
    inline Options operator & (Options lhs, Options rhs)
    {
        return static_cast<Options>(static_cast<int>(lhs) & static_cast<int>(rhs));
    }
 
    class FlagBase;
    class PositionalBase;
    class Command;
    class ArgumentParser;
 
    struct HelpParams
    {
        unsigned int width = 80;
        unsigned int progindent = 2;
        unsigned int progtailindent = 4;
        unsigned int descriptionindent = 4;
        unsigned int flagindent = 6;
        unsigned int helpindent = 40;
        unsigned int eachgroupindent = 2;
 
        unsigned int gutter = 1;
 
        bool showTerminator = true;
 
        bool showProglineOptions = true;
 
        bool showProglinePositionals = true;
 
        std::string shortPrefix;
 
        std::string longPrefix;
 
        std::string shortSeparator;
 
        std::string longSeparator;
 
        std::string programName;
 
        bool showCommandChildren = false;
 
        bool showCommandFullHelp = false;
 
        std::string proglineOptions = "{OPTIONS}";
 
        std::string proglineCommand = "COMMAND";
 
        std::string proglineValueOpen = " <";
 
        std::string proglineValueClose = ">";
 
        std::string proglineRequiredOpen = "";
 
        std::string proglineRequiredClose = "";
 
        std::string proglineNonrequiredOpen = "[";
 
        std::string proglineNonrequiredClose = "]";
 
        bool proglineShowFlags = false;
 
        bool proglinePreferShortFlags = false;
 
        std::string usageString;
 
        std::string optionsString = "OPTIONS:";
 
        bool useValueNameOnce = false;
 
        bool showValueName = true;
 
        bool addNewlineBeforeDescription = false;
 
        std::string valueOpen = "[";
 
        std::string valueClose = "]";
 
        bool addChoices = false;
 
        std::string choiceString = "\nOne of: ";
 
        bool addDefault = false;
 
        std::string defaultString = "\nDefault: ";
    };
 
    struct Nargs
    {
        const size_t min;
        const size_t max;
 
        Nargs(size_t min_, size_t max_) : min{min_}, max{max_}
        {
#ifndef ARGS_NOEXCEPT
            if (max < min)
            {
                throw UsageError("Nargs: max < min");
            }
#endif
        }
 
        Nargs(size_t num_) : min{num_}, max{num_}
        {
        }
 
        friend bool operator == (const Nargs &lhs, const Nargs &rhs)
        {
            return lhs.min == rhs.min && lhs.max == rhs.max;
        }
 
        friend bool operator != (const Nargs &lhs, const Nargs &rhs)
        {
            return !(lhs == rhs);
        }
    };
 
    class Base
    {
        private:
            Options options = {};
 
        protected:
            bool matched = false;
            const std::string help;
#ifdef ARGS_NOEXCEPT
            mutable Error error = Error::None;
            mutable std::string errorMsg;
#endif
 
        public:
            Base(const std::string &help_, Options options_ = {}) : options(options_), help(help_) {}
            virtual ~Base() {}
 
            Options GetOptions() const noexcept
            {
                return options;
            }
 
            bool IsRequired() const noexcept
            {
                return (GetOptions() & Options::Required) != Options::None;
            }
 
            virtual bool Matched() const noexcept
            {
                return matched;
            }
 
            virtual void Validate(const std::string &, const std::string &) const
            {
            }
 
            operator bool() const noexcept
            {
                return Matched();
            }
 
            virtual std::vector<std::tuple<std::string, std::string, unsigned>> GetDescription(const HelpParams &, const unsigned indentLevel) const
            {
                std::tuple<std::string, std::string, unsigned> description;
                std::get<1>(description) = help;
                std::get<2>(description) = indentLevel;
                return { std::move(description) };
            }
 
            virtual std::vector<Command*> GetCommands()
            {
                return {};
            }
 
            virtual bool IsGroup() const
            {
                return false;
            }
 
            virtual bool IsFlag() const
            {
                return false;
            }
 
            virtual FlagBase *Match(const EitherFlag &)
            {
                return nullptr;
            }
 
            virtual PositionalBase *GetNextPositional()
            {
                return nullptr;
            }
 
            virtual std::vector<FlagBase*> GetAllFlags()
            {
                return {};
            }
 
            virtual bool HasFlag() const
            {
                return false;
            }
 
            virtual bool HasPositional() const
            {
                return false;
            }
 
            virtual bool HasCommand() const
            {
                return false;
            }
 
            virtual std::vector<std::string> GetProgramLine(const HelpParams &) const
            {
                return {};
            }
 
            void KickOut(bool kickout_) noexcept
            {
                if (kickout_)
                {
                    options = options | Options::KickOut;
                }
                else
                {
                    options = static_cast<Options>(static_cast<int>(options) & ~static_cast<int>(Options::KickOut));
                }
            }
 
            bool KickOut() const noexcept
            {
                return (options & Options::KickOut) != Options::None;
            }
 
            virtual void Reset() noexcept
            {
                matched = false;
#ifdef ARGS_NOEXCEPT
                error = Error::None;
                errorMsg.clear();
#endif
            }
 
#ifdef ARGS_NOEXCEPT
            virtual Error GetError() const
            {
                return error;
            }
 
            virtual std::string GetErrorMsg() const
            {
                return errorMsg;
            }
#endif
    };
 
    class NamedBase : public Base
    {
        protected:
            const std::string name;
            bool kickout = false;
            std::string defaultString;
            bool defaultStringManual = false;
            std::vector<std::string> choicesStrings;
            bool choicesStringManual = false;
 
            virtual std::string GetDefaultString(const HelpParams&) const { return {}; }
 
            virtual std::vector<std::string> GetChoicesStrings(const HelpParams&) const { return {}; }
 
            virtual std::string GetNameString(const HelpParams&) const { return Name(); }
 
            void AddDescriptionPostfix(std::string &dest, const bool isManual, const std::string &manual, bool isGenerated, const std::string &generated, const std::string &str) const
            {
                if (isManual && !manual.empty())
                {
                    dest += str;
                    dest += manual;
                }
                else if (!isManual && isGenerated && !generated.empty())
                {
                    dest += str;
                    dest += generated;
                }
            }
 
        public:
            NamedBase(const std::string &name_, const std::string &help_, Options options_ = {}) : Base(help_, options_), name(name_) {}
            virtual ~NamedBase() {}
 
            void HelpDefault(const std::string &str)
            {
                defaultStringManual = true;
                defaultString = str;
            }
 
            std::string HelpDefault(const HelpParams &params) const
            {
                return defaultStringManual ? defaultString : GetDefaultString(params);
            }
 
            void HelpChoices(const std::vector<std::string> &array)
            {
                choicesStringManual = true;
                choicesStrings = array;
            }
 
            std::vector<std::string> HelpChoices(const HelpParams &params) const
            {
                return choicesStringManual ? choicesStrings : GetChoicesStrings(params);
            }
 
            virtual std::vector<std::tuple<std::string, std::string, unsigned>> GetDescription(const HelpParams &params, const unsigned indentLevel) const override
            {
                std::tuple<std::string, std::string, unsigned> description;
                std::get<0>(description) = GetNameString(params);
                std::get<1>(description) = help;
                std::get<2>(description) = indentLevel;
 
                AddDescriptionPostfix(std::get<1>(description), choicesStringManual, detail::Join(choicesStrings, ", "), params.addChoices, detail::Join(GetChoicesStrings(params), ", "), params.choiceString);
                AddDescriptionPostfix(std::get<1>(description), defaultStringManual, defaultString, params.addDefault, GetDefaultString(params), params.defaultString);
 
                return { std::move(description) };
            }
 
            virtual std::string Name() const
            {
                return name;
            }
    };
 
    namespace detail
    {
        template<typename T>
        using vector = std::vector<T, std::allocator<T>>;
        
        template<typename K, typename T>
        using unordered_map = std::unordered_map<K, T, std::hash<K>, 
            std::equal_to<K>, std::allocator<std::pair<const K, T> > >;
 
        template<typename S, typename T>
        class is_streamable
        {
            template<typename SS, typename TT>
            static auto test(int)
            -> decltype( std::declval<SS&>() << std::declval<TT>(), std::true_type() );
 
            template<typename, typename>
            static auto test(...) -> std::false_type;
 
        public:
            using type = decltype(test<S,T>(0));
        };
 
        template <typename T>
        using IsConvertableToString = typename is_streamable<std::ostringstream, T>::type;
 
        template <typename T>
        typename std::enable_if<IsConvertableToString<T>::value, std::string>::type
        ToString(const T &value)
        {
            std::ostringstream s;
            s << value;
            return s.str();
        }
 
        template <typename T>
        typename std::enable_if<!IsConvertableToString<T>::value, std::string>::type
        ToString(const T &)
        {
            return {};
        }
 
        // Keep emplace_back for sequences: insert can require move assignment
        // even when appending a copyable value at the end of a vector.
        template <typename Container, typename T>
        auto AppendMappedValue(Container &container, const T &value, int)
            -> decltype(container.emplace_back(value), void())
        {
            container.emplace_back(value);
        }
 
        template <typename Container, typename T>
        auto AppendMappedValue(Container &container, const T &value, long)
            -> decltype(container.insert(std::end(container), value), void())
        {
            container.insert(std::end(container), value);
        }
 
        template <typename T>
        std::vector<std::string> MapKeysToStrings(const T &map)
        {
            std::vector<std::string> res;
            using K = typename std::decay<decltype(std::begin(map)->first)>::type;
            if (IsConvertableToString<K>::value)
            {
                for (const auto &p : map)
                {
                    res.push_back(detail::ToString(p.first));
                }
 
                std::sort(res.begin(), res.end());
            }
            return res;
        }
    }
 
    class FlagBase : public NamedBase
    {
        protected:
            const Matcher matcher;
 
            virtual std::string GetNameString(const HelpParams &params) const override
            {
                const std::string postfix = !params.showValueName || NumberOfArguments() == 0 ? std::string() : Name();
                std::string flags;
                const auto flagStrings = matcher.GetFlagStrings();
                const bool useValueNameOnce = flagStrings.size() == 1 ? false : params.useValueNameOnce;
                for (auto it = flagStrings.begin(); it != flagStrings.end(); ++it)
                {
                    auto &flag = *it;
                    if (it != flagStrings.begin())
                    {
                        flags += ", ";
                    }
 
                    flags += flag.isShort ? params.shortPrefix : params.longPrefix;
                    flags += flag.str();
 
                    if (!postfix.empty() && (!useValueNameOnce || it + 1 == flagStrings.end()))
                    {
                        flags += flag.isShort ? params.shortSeparator : params.longSeparator;
                        flags += params.valueOpen + postfix + params.valueClose;
                    }
                }
 
                return flags;
            }
 
        public:
            FlagBase(const std::string &name_, const std::string &help_, Matcher &&matcher_, const bool extraError_ = false) : NamedBase(name_, help_, extraError_ ? Options::Single : Options()), matcher(std::move(matcher_)) {}
 
            FlagBase(const std::string &name_, const std::string &help_, Matcher &&matcher_, Options options_) : NamedBase(name_, help_, options_), matcher(std::move(matcher_)) {}
 
            virtual ~FlagBase() {}
 
            virtual bool IsFlag() const override
            {
                return true;
            }
 
            virtual FlagBase *Match(const EitherFlag &flag) override
            {
                if (matcher.Match(flag))
                {
                    if ((GetOptions() & Options::Single) != Options::None && matched)
                    {
                        std::ostringstream problem;
                        problem << "Flag '" << flag.str() << "' was passed multiple times, but is only allowed to be passed once";
#ifdef ARGS_NOEXCEPT
                        error = Error::Extra;
                        errorMsg = problem.str();
#else
                        throw ExtraError(problem.str());
#endif
                    }
                    matched = true;
                    return this;
                }
                return nullptr;
            }
 
            virtual std::vector<FlagBase*> GetAllFlags() override
            {
                return { this };
            }
 
            const Matcher &GetMatcher() const
            {
                return matcher;
            }
 
            virtual void Validate(const std::string &shortPrefix, const std::string &longPrefix) const override
            {
                if (!Matched() && IsRequired())
                {
                        std::ostringstream problem;
                        problem << "Flag '" << matcher.GetLongOrAny().str(shortPrefix, longPrefix) << "' is required";
#ifdef ARGS_NOEXCEPT
                        error = Error::Required;
                        errorMsg = problem.str();
#else
                        throw RequiredError(problem.str());
#endif
                }
            }
 
            virtual std::vector<std::string> GetProgramLine(const HelpParams &params) const override
            {
                if (!params.proglineShowFlags)
                {
                    return {};
                }
 
                const std::string postfix = NumberOfArguments() == 0 ? std::string() : Name();
                const EitherFlag flag = params.proglinePreferShortFlags ? matcher.GetShortOrAny() : matcher.GetLongOrAny();
                std::string res = flag.str(params.shortPrefix, params.longPrefix);
                if (!postfix.empty())
                {
                    res += params.proglineValueOpen + postfix + params.proglineValueClose;
                }
 
                return { IsRequired() ? params.proglineRequiredOpen + res + params.proglineRequiredClose
                                      : params.proglineNonrequiredOpen + res + params.proglineNonrequiredClose };
            }
 
            virtual bool HasFlag() const override
            {
                return true;
            }
 
#ifdef ARGS_NOEXCEPT
            bool usageError = false;
            void SetUsageError()
            {
                usageError = true;
            }
            void ClearUsageError()
            {
                usageError = false;
            }
            virtual Error GetError() const override
            {
                if(usageError)
                {
                    return Error::Usage;
                }
                const auto nargs = NumberOfArguments();
                if (nargs.min > nargs.max)
                {
                    return Error::Usage;
                }
 
                const auto matcherError = matcher.GetError();
                if (matcherError != Error::None)
                {
                    return matcherError;
                }
 
                return error;
            }
#endif
 
            virtual Nargs NumberOfArguments() const noexcept = 0;
 
            virtual void ParseValue(const std::vector<std::string> &value) = 0;
    };
 
    class ValueFlagBase : public FlagBase
    {
        public:
            ValueFlagBase(const std::string &name_, const std::string &help_, Matcher &&matcher_, const bool extraError_ = false) : FlagBase(name_, help_, std::move(matcher_), extraError_) {}
            ValueFlagBase(const std::string &name_, const std::string &help_, Matcher &&matcher_, Options options_) : FlagBase(name_, help_, std::move(matcher_), options_) {}
            virtual ~ValueFlagBase() {}
 
            virtual Nargs NumberOfArguments() const noexcept override
            {
                return 1;
            }
    };
 
    class CompletionFlag : public ValueFlagBase
    {
        public:
            std::vector<std::string> reply;
            size_t cword = 0;
            std::string syntax;
 
            template <typename GroupClass>
            CompletionFlag(GroupClass &group_, Matcher &&matcher_): ValueFlagBase("completion", "completion flag", std::move(matcher_), Options::Hidden)
            {
                group_.AddCompletion(*this);
            }
 
            virtual ~CompletionFlag() {}
 
            virtual Nargs NumberOfArguments() const noexcept override
            {
                return 2;
            }
 
            virtual void ParseValue(const std::vector<std::string> &value_) override
            {
                syntax = value_.at(0);
                const std::string &raw = value_.at(1);
                bool failed = false;
 
                const auto firstNonSpace = std::find_if_not(raw.begin(), raw.end(), [](char c)
                {
                    return std::isspace(static_cast<unsigned char>(c)) != 0;
                });
 
                // Reject explicit signs: cword must be a plain non-negative
                // decimal index. istringstream would otherwise silently
                // accept "+1".
                if (firstNonSpace != raw.end() && (*firstNonSpace == '-' || *firstNonSpace == '+'))
                {
                    failed = true;
                }
 
                size_t parsed = 0;
                if (!failed)
                {
                    std::istringstream ss(raw);
                    // Use the C locale so that the cword index parses
                    // consistently regardless of any std::locale::global call
                    // elsewhere in the process. A locale with a non-empty
                    // grouping facet would otherwise reject digit-only inputs
                    // like "12" when grouping rules expect separators.
                    ss.imbue(std::locale::classic());
                    ss >> parsed;
                    if (ss.fail())
                    {
                        failed = true;
                    }
                    else
                    {
                        char extra;
                        if (ss >> extra)
                        {
                            failed = true;
                        }
                        else if (!ss.eof())
                        {
                            failed = true;
                        }
                    }
                }
 
                if (failed)
                {
#ifdef ARGS_NOEXCEPT
                    error = Error::Parse;
                    errorMsg = "Argument 'completion' received invalid value type '" + raw + "'";
#else
                    std::ostringstream problem;
                    problem << "Argument 'completion' received invalid value type '" << raw << "'";
                    throw ParseError(problem.str());
#endif
                    return;
                }
 
                cword = parsed;
            }
 
            std::string Get() noexcept
            {
                return detail::Join(reply, "\n");
            }
 
            virtual void Reset() noexcept override
            {
                ValueFlagBase::Reset();
                cword = 0;
                syntax.clear();
                reply.clear();
            }
    };
 
 
    class PositionalBase : public NamedBase
    {
        protected:
            bool ready;
 
        public:
            PositionalBase(const std::string &name_, const std::string &help_, Options options_ = {}) : NamedBase(name_, help_, options_), ready(true) {}
            virtual ~PositionalBase() {}
 
            bool Ready()
            {
                return ready;
            }
 
            virtual void ParseValue(const std::string &value_) = 0;
 
            virtual void Reset() noexcept override
            {
                matched = false;
                ready = true;
#ifdef ARGS_NOEXCEPT
                error = Error::None;
                errorMsg.clear();
#endif
            }
 
            virtual PositionalBase *GetNextPositional() override
            {
                return Ready() ? this : nullptr;
            }
 
            virtual bool HasPositional() const override
            {
                return true;
            }
 
            virtual std::vector<std::string> GetProgramLine(const HelpParams &params) const override
            {
                return { IsRequired() ? params.proglineRequiredOpen + Name() + params.proglineRequiredClose
                                      : params.proglineNonrequiredOpen + Name() + params.proglineNonrequiredClose };
            }
 
            virtual void Validate(const std::string &, const std::string &) const override
            {
                if (IsRequired() && !Matched())
                {
                    std::ostringstream problem;
                    problem << "Option '" << Name() << "' is required";
#ifdef ARGS_NOEXCEPT
                    error = Error::Required;
                    errorMsg = problem.str();
#else
                    throw RequiredError(problem.str());
#endif
                }
            }
    };
 
    class Group : public Base
    {
        private:
            Group* parent;
            std::vector<Base*> children;
            std::function<bool(const Group &)> validator;
 
        public:
            struct Validators
            {
                static bool Xor(const Group &group)
                {
                    return group.MatchedChildren() == 1;
                }
 
                static bool AtLeastOne(const Group &group)
                {
                    return group.MatchedChildren() >= 1;
                }
 
                static bool AtMostOne(const Group &group)
                {
                    return group.MatchedChildren() <= 1;
                }
 
                static bool All(const Group &group)
                {
                    return group.Children().size() == group.MatchedChildren();
                }
 
                static bool AllOrNone(const Group &group)
                {
                    return (All(group) || None(group));
                }
 
                static bool AllChildGroups(const Group &group)
                {
                    return std::none_of(std::begin(group.Children()), std::end(group.Children()), [](const Base* child) -> bool {
                            return child->IsGroup() && !child->Matched();
                            });
                }
 
                static bool DontCare(const Group &)
                {
                    return true;
                }
 
                static bool CareTooMuch(const Group &)
                {
                    return false;
                }
 
                static bool None(const Group &group)
                {
                    return group.MatchedChildren() == 0;
                }
            };
            Group(const std::string &help_ = std::string(), const std::function<bool(const Group &)> &validator_ = Validators::DontCare, Options options_ = {}) : Base(help_, options_), validator(validator_)
            {
                parent = nullptr;
            }
            Group(Group &group_, const std::string &help_ = std::string(), const std::function<bool(const Group &)> &validator_ = Validators::DontCare, Options options_ = {}) : Base(help_, options_), validator(validator_)
            {
                group_.Add(*this);
                parent = &group_;
            }
            virtual ~Group() {}
 
            void Add(Base &child)
            {
                children.emplace_back(&child);
 
                if(child.IsFlag()) {
#ifndef ARGS_NOEXCEPT
                    // Detection runs from the child's own constructor, so a
                    // duplicate throws before that constructor completes and the
                    // child's storage is released while the stack unwinds. Undo
                    // the registration first, or a caller that catches the error
                    // leaves this group holding a pointer to a dead object.
                    try
                    {
                        SignalDetectDuplicates();
                    }
                    catch (...)
                    {
                        children.pop_back();
                        throw;
                    }
#else
                    SignalDetectDuplicates();
#endif
                }
            }
 
            const std::vector<Base *> &Children() const
            {
                return children;
            }
 
            virtual FlagBase *Match(const EitherFlag &flag) override
            {
                for (Base *child: Children())
                {
                    if (FlagBase *match = child->Match(flag))
                    {
                        return match;
                    }
                }
                return nullptr;
            }
 
            virtual std::vector<FlagBase*> GetAllFlags() override
            {
                std::vector<FlagBase*> res;
                for (Base *child: Children())
                {
                    auto childRes = child->GetAllFlags();
                    res.insert(res.end(), childRes.begin(), childRes.end());
                }
                return res;
            }
 
            virtual void Validate(const std::string &shortPrefix, const std::string &longPrefix) const override
            {
                for (Base *child: Children())
                {
                    child->Validate(shortPrefix, longPrefix);
                }
            }
 
            virtual PositionalBase *GetNextPositional() override
            {
                for (Base *child: Children())
                {
                    if (auto next = child->GetNextPositional())
                    {
                        return next;
                    }
                }
                return nullptr;
            }
 
            virtual bool HasFlag() const override
            {
                return std::any_of(Children().begin(), Children().end(), [](Base *child) { return child->HasFlag(); });
            }
 
            virtual bool HasPositional() const override
            {
                return std::any_of(Children().begin(), Children().end(), [](Base *child) { return child->HasPositional(); });
            }
 
            virtual bool HasCommand() const override
            {
                return std::any_of(Children().begin(), Children().end(), [](Base *child) { return child->HasCommand(); });
            }
 
            std::vector<Base *>::size_type MatchedChildren() const
            {
                // Cast to avoid warnings from -Wsign-conversion
                return static_cast<std::vector<Base *>::size_type>(
                        std::count_if(std::begin(Children()), std::end(Children()), [](const Base *child){return child->Matched();}));
            }
 
            std::vector<Base *> GetMatchedChildren() const
            {
                // Could be replaced by C++ 20 filter, or a custom iterator.
                std::vector<Base*> matched_children;
                std::copy_if(children.begin(), children.end(), std::back_inserter(matched_children), [](Base* b){
                    return b->Matched();
                });
                return matched_children;
            }
 
             template <typename ChildType>
             std::vector<ChildType *> GetFilteredChildren(bool matching = false) const
             {
                std::vector<ChildType *> filtered_children;
                for(Base *child : children) {
                    if(!matching || child->Matched())
                    {
                        ChildType* cast_result = dynamic_cast<ChildType*>(child);
                        if(cast_result != nullptr)
                        {
                            filtered_children.push_back(cast_result);
                        }
 
                    }
                }
                return filtered_children;
             }
 
            virtual bool Matched() const noexcept override
            {
                return validator(*this);
            }
 
            bool Get() const
            {
                return Matched();
            }
 
            virtual std::vector<std::tuple<std::string, std::string, unsigned>> GetDescription(const HelpParams &params, const unsigned int indent) const override
            {
                std::vector<std::tuple<std::string, std::string, unsigned int>> descriptions;
 
                // Push that group description on the back if not empty
                unsigned addindent = 0;
                if (!help.empty())
                {
                    descriptions.emplace_back(help, "", indent);
                    addindent = 1;
                }
 
                for (Base *child: Children())
                {
                    if ((child->GetOptions() & Options::HiddenFromDescription) != Options::None)
                    {
                        continue;
                    }
 
                    auto groupDescriptions = child->GetDescription(params, indent + addindent);
                    descriptions.insert(
                        std::end(descriptions),
                        std::make_move_iterator(std::begin(groupDescriptions)),
                        std::make_move_iterator(std::end(groupDescriptions)));
                }
                return descriptions;
            }
 
            virtual std::vector<std::string> GetProgramLine(const HelpParams &params) const override
            {
                std::vector <std::string> names;
                for (Base *child: Children())
                {
                    if ((child->GetOptions() & Options::HiddenFromUsage) != Options::None)
                    {
                        continue;
                    }
 
                    auto groupNames = child->GetProgramLine(params);
                    names.insert(
                        std::end(names),
                        std::make_move_iterator(std::begin(groupNames)),
                        std::make_move_iterator(std::end(groupNames)));
                }
                return names;
            }
 
            virtual std::vector<Command*> GetCommands() override
            {
                std::vector<Command*> res;
                for (const auto &child : Children())
                {
                    auto subparsers = child->GetCommands();
                    res.insert(std::end(res), std::begin(subparsers), std::end(subparsers));
                }
                return res;
            }
 
            virtual bool IsGroup() const override
            {
                return true;
            }
 
            virtual void Reset() noexcept override
            {
                Base::Reset();
 
                for (auto &child: Children())
                {
                    child->Reset();
                }
#ifdef ARGS_NOEXCEPT
                error = Error::None;
                errorMsg.clear();
#endif
            }
 
            void SignalDetectDuplicates()
            {
                if(parent != nullptr) parent->SignalDetectDuplicates();
                else DetectDuplicateFlags();
            }
 
            void DetectDuplicateFlags()
            {
                std::unordered_set<char> usedShortFlags;
                std::unordered_set<std::string> usedLongFlags;
                DetectDuplicateFlags(usedShortFlags, usedLongFlags);
            }
        
            void DetectDuplicateFlags(std::unordered_set<char> &usedShortFlags, std::unordered_set<std::string> &usedLongFlags)
            {
                for (Base *child: Children())
                {
                    if(auto flag = dynamic_cast<FlagBase*>(child))
                    {
                        // Check for duplicate flags, setting a usage error on the
                        // flag if a duplicate is detected.
                        for(EitherFlag flagString: flag->GetMatcher().GetFlagStrings())
                        {
                            if(flagString.isShort)
                            {
                                if(usedShortFlags.count(flagString.shortFlag))
                                {
#ifdef ARGS_NOEXCEPT
                                    flag->SetUsageError();
#else
                                    throw ParseError("duplicate short flag detected");
#endif
                                }
                                else
                                {
                                    usedShortFlags.insert(flagString.shortFlag);
                                }
                            }
                            else
                            {
                                if(usedLongFlags.count(flagString.longFlag))
                                {
#ifdef ARGS_NOEXCEPT
                                    flag->SetUsageError();
#else
                                    throw ParseError("duplicate long flag detected");
#endif
                                }
                                else
                                {
                                    usedLongFlags.insert(flagString.longFlag);
                                }
                            }
                        }
                    }
                    else if(auto group = dynamic_cast<Group*>(child))
                    {
                        // A command opens its own flag namespace and runs its
                        // own duplicate detection as a separate root, so a flag
                        // reused either side of a command boundary is not a
                        // genuine duplicate. Only descend into plain groups
                        // here; IsGroup() is false for a Command.
                        if(group->IsGroup())
                        {
                            group->DetectDuplicateFlags(usedShortFlags, usedLongFlags);
                        }
                    }
                }
            }
 
#ifdef ARGS_NOEXCEPT
            virtual Error GetError() const override
            {
                if (error != Error::None)
                {
                    return error;
                }
 
                auto it = std::find_if(Children().begin(), Children().end(), [](const Base *child){return child->GetError() != Error::None;});
                if (it == Children().end())
                {
                    return Error::None;
                } else
                {
                    return (*it)->GetError();
                }
            }
 
            virtual std::string GetErrorMsg() const override
            {
                if (error != Error::None)
                {
                    return errorMsg;
                }
 
                auto it = std::find_if(Children().begin(), Children().end(), [](const Base *child){return child->GetError() != Error::None;});
                if (it == Children().end())
                {
                    return "";
                } else
                {
                    return (*it)->GetErrorMsg();
                }
            }
#endif
 
    };
 
    class GlobalOptions : public Group
    {
        public:
            GlobalOptions(Group &base, Base &options_) : Group(base, {}, Group::Validators::DontCare, Options::Global)
            {
                Add(options_);
            }
    };
 
    class Subparser : public Group
    {
        private:
            std::vector<std::string> args;
            std::vector<std::string> kicked;
            ArgumentParser *parser = nullptr;
            const HelpParams &helpParams;
            const Command &command;
            bool isParsed = false;
 
        public:
            Subparser(std::vector<std::string> args_, ArgumentParser &parser_, const Command &command_, const HelpParams &helpParams_)
                : Group({}, Validators::AllChildGroups), args(std::move(args_)), parser(&parser_), helpParams(helpParams_), command(command_)
            {
            }
 
            Subparser(const Command &command_, const HelpParams &helpParams_) : Group({}, Validators::AllChildGroups), helpParams(helpParams_), command(command_)
            {
            }
 
            Subparser(const Subparser&) = delete;
            Subparser(Subparser&&) = delete;
            Subparser &operator = (const Subparser&) = delete;
            Subparser &operator = (Subparser&&) = delete;
 
            const Command &GetCommand()
            {
                return command;
            }
 
            bool IsParsed() const
            {
                return isParsed;
            }
 
            void Parse();
 
            const std::vector<std::string> &KickedOut() const noexcept
            {
                return kicked;
            }
    };
 
    class Command : public Group
    {
        private:
            friend class Subparser;
 
            std::string name;
            std::string help;
            std::string description;
            std::string epilog;
            std::string proglinePostfix;
 
            std::function<void(Subparser&)> parserCoroutine;
            bool commandIsRequired = true;
            Command *selectedCommand = nullptr;
 
            mutable std::vector<std::tuple<std::string, std::string, unsigned>> subparserDescription;
            mutable std::vector<std::string> subparserProgramLine;
            mutable bool subparserHasFlag = false;
            mutable bool subparserHasPositional = false;
            mutable bool subparserHasCommand = false;
#ifdef ARGS_NOEXCEPT
            mutable Error subparserError = Error::None;
#endif
            mutable Subparser *subparser = nullptr;
 
        protected:
 
            class RaiiSubparser
            {
                public:
                    RaiiSubparser(ArgumentParser &parser_, std::vector<std::string> args_);
                    RaiiSubparser(const Command &command_, const HelpParams &params_);
 
                    ~RaiiSubparser()
                    {
                        command.subparser = oldSubparser;
                    }
 
                    Subparser &Parser()
                    {
                        return parser;
                    }
 
                private:
                    const Command &command;
                    Subparser parser;
                    Subparser *oldSubparser;
            };
 
            Command() = default;
 
            std::function<void(Subparser&)> &GetCoroutine()
            {
                return selectedCommand != nullptr ? selectedCommand->GetCoroutine() : parserCoroutine;
            }
 
            Command &SelectedCommand()
            {
                Command *res = this;
                while (res->selectedCommand != nullptr)
                {
                    res = res->selectedCommand;
                }
 
                return *res;
            }
 
            const Command &SelectedCommand() const
            {
                const Command *res = this;
                while (res->selectedCommand != nullptr)
                {
                    res = res->selectedCommand;
                }
 
                return *res;
            }
 
            void UpdateSubparserHelp(const HelpParams &params) const
            {
                if (parserCoroutine)
                {
                    RaiiSubparser coro(*this, params);
#ifndef ARGS_NOEXCEPT
                    try
                    {
                        parserCoroutine(coro.Parser());
                    }
                    catch (args::SubparserError&)
                    {
                    }
#else
                    parserCoroutine(coro.Parser());
#endif
                }
            }
 
        public:
            Command(Group &base_, std::string name_, std::string help_, std::function<void(Subparser&)> coroutine_ = {})
                : name(std::move(name_)), help(std::move(help_)), parserCoroutine(std::move(coroutine_))
            {
                base_.Add(*this);
            }
 
            const std::string &ProglinePostfix() const
            { return proglinePostfix; }
 
            void ProglinePostfix(const std::string &proglinePostfix_)
            { this->proglinePostfix = proglinePostfix_; }
 
            const std::string &Description() const
            { return description; }
            void Description(const std::string &description_)
            { this->description = description_; }
 
            const std::string &Epilog() const
            { return epilog; }
 
            void Epilog(const std::string &epilog_)
            { this->epilog = epilog_; }
 
            const std::string &Name() const
            { return name; }
 
            const std::string &Help() const
            { return help; }
 
            void RequireCommand(bool value)
            { commandIsRequired = value; }
 
            virtual bool IsGroup() const override
            { return false; }
 
            virtual bool Matched() const noexcept override
            { return Base::Matched(); }
 
            operator bool() const noexcept
            { return Matched(); }
 
            void Match() noexcept
            { matched = true; }
 
            void SelectCommand(Command *c) noexcept
            {
                selectedCommand = c;
 
                if (c != nullptr)
                {
                    c->Match();
                }
            }
 
            virtual FlagBase *Match(const EitherFlag &flag) override
            {
                if (selectedCommand != nullptr)
                {
                    if (auto *res = selectedCommand->Match(flag))
                    {
                        return res;
                    }
 
                    for (auto *child: Children())
                    {
                        if ((child->GetOptions() & Options::Global) != Options::None)
                        {
                            if (auto *res = child->Match(flag))
                            {
                                return res;
                            }
                        }
                    }
 
                    return nullptr;
                }
 
                if (subparser != nullptr)
                {
                    return subparser->Match(flag);
                }
 
                return Matched() ? Group::Match(flag) : nullptr;
            }
 
            virtual std::vector<FlagBase*> GetAllFlags() override
            {
                std::vector<FlagBase*> res;
 
                if (!Matched())
                {
                    return res;
                }
 
                for (auto *child: Children())
                {
                    if (selectedCommand == nullptr || (child->GetOptions() & Options::Global) != Options::None)
                    {
                        auto childFlags = child->GetAllFlags();
                        res.insert(res.end(), childFlags.begin(), childFlags.end());
                    }
                }
 
                if (selectedCommand != nullptr)
                {
                    auto childFlags = selectedCommand->GetAllFlags();
                    res.insert(res.end(), childFlags.begin(), childFlags.end());
                }
 
                if (subparser != nullptr)
                {
                    auto childFlags = subparser->GetAllFlags();
                    res.insert(res.end(), childFlags.begin(), childFlags.end());
                }
 
                return res;
            }
 
            virtual PositionalBase *GetNextPositional() override
            {
                if (selectedCommand != nullptr)
                {
                    if (auto *res = selectedCommand->GetNextPositional())
                    {
                        return res;
                    }
 
                    for (auto *child: Children())
                    {
                        if ((child->GetOptions() & Options::Global) != Options::None)
                        {
                            if (auto *res = child->GetNextPositional())
                            {
                                return res;
                            }
                        }
                    }
 
                    return nullptr;
                }
 
                if (subparser != nullptr)
                {
                    return subparser->GetNextPositional();
                }
 
                return Matched() ? Group::GetNextPositional() : nullptr;
            }
 
            virtual bool HasFlag() const override
            {
                return subparserHasFlag || Group::HasFlag();
            }
 
            virtual bool HasPositional() const override
            {
                return subparserHasPositional || Group::HasPositional();
            }
 
            virtual bool HasCommand() const override
            {
                return true;
            }
 
            std::vector<std::string> GetCommandProgramLine(const HelpParams &params) const
            {
                UpdateSubparserHelp(params);
 
                std::vector<std::string> res;
 
                if ((subparserHasFlag || Group::HasFlag()) && params.showProglineOptions && !params.proglineShowFlags)
                {
                    res.push_back(params.proglineOptions);
                }
 
                auto group_res = Group::GetProgramLine(params);
                std::move(std::move(group_res).begin(), std::move(group_res).end(), std::back_inserter(res));
 
                res.insert(res.end(), subparserProgramLine.begin(), subparserProgramLine.end());
 
                if (!params.proglineCommand.empty() && (Group::HasCommand() || subparserHasCommand))
                {
                    res.insert(res.begin(), commandIsRequired ? params.proglineCommand : "[" + params.proglineCommand + "]");
                }
 
                if (!Name().empty())
                {
                    res.insert(res.begin(), Name());
                }
 
                if (!ProglinePostfix().empty())
                {
                    std::string line;
                    for (auto c : ProglinePostfix())
                    {
                        if (std::isspace(static_cast<unsigned char>(c)))
                        {
                            if (!line.empty())
                            {
                                res.push_back(line);
                                line.clear();
                            }
 
                            if (c == '\n')
                            {
                                res.push_back("\n");
                            }
                        }
                        else
                        {
                            line += c;
                        }
                    }
 
                    if (!line.empty())
                    {
                        res.push_back(line);
                    }
                }
 
                return res;
            }
 
            virtual std::vector<std::string> GetProgramLine(const HelpParams &params) const override
            {
                if (!Matched())
                {
                    return {};
                }
 
                return GetCommandProgramLine(params);
            }
 
            virtual std::vector<Command*> GetCommands() override
            {
                if (selectedCommand != nullptr)
                {
                    return selectedCommand->GetCommands();
                }
 
                if (Matched())
                {
                    return Group::GetCommands();
                }
 
                return { this };
            }
 
            virtual std::vector<std::tuple<std::string, std::string, unsigned>> GetDescription(const HelpParams &params, const unsigned int indent) const override
            {
                std::vector<std::tuple<std::string, std::string, unsigned>> descriptions;
                unsigned addindent = 0;
 
                UpdateSubparserHelp(params);
 
                if (!Matched())
                {
                    if (params.showCommandFullHelp)
                    {
                        std::ostringstream s;
                        bool empty = true;
                        for (const auto &progline: GetCommandProgramLine(params))
                        {
                            if (!empty)
                            {
                                s << ' ';
                            }
                            else
                            {
                                empty = false;
                            }
 
                            s << progline;
                        }
 
                        descriptions.emplace_back(s.str(), "", indent);
                    }
                    else
                    {
                        descriptions.emplace_back(Name(), help, indent);
                    }
 
                    if (!params.showCommandChildren && !params.showCommandFullHelp)
                    {
                        return descriptions;
                    }
 
                    addindent = 1;
                }
 
                if (params.showCommandFullHelp && !Matched())
                {
                    descriptions.emplace_back("", "", indent + addindent);
                    descriptions.emplace_back(Description().empty() ? Help() : Description(), "", indent + addindent);
                    descriptions.emplace_back("", "", indent + addindent);
                }
 
                for (Base *child: Children())
                {
                    if ((child->GetOptions() & Options::HiddenFromDescription) != Options::None)
                    {
                        continue;
                    }
 
                    auto groupDescriptions = child->GetDescription(params, indent + addindent);
                    descriptions.insert(
                                        std::end(descriptions),
                                        std::make_move_iterator(std::begin(groupDescriptions)),
                                        std::make_move_iterator(std::end(groupDescriptions)));
                }
 
                for (auto childDescription: subparserDescription)
                {
                    std::get<2>(childDescription) += indent + addindent;
                    descriptions.push_back(std::move(childDescription));
                }
 
                if (params.showCommandFullHelp && !Matched())
                {
                    descriptions.emplace_back("", "", indent + addindent);
                    if (!Epilog().empty())
                    {
                        descriptions.emplace_back(Epilog(), "", indent + addindent);
                        descriptions.emplace_back("", "", indent + addindent);
                    }
                }
 
                return descriptions;
            }
 
            virtual void Validate(const std::string &shortprefix, const std::string &longprefix) const override
            {
                if (!Matched())
                {
                    return;
                }
 
                auto onValidationError = [&]
                {
                    std::ostringstream problem;
                    problem << "Group validation failed somewhere!";
#ifdef ARGS_NOEXCEPT
                    error = Error::Validation;
                    errorMsg = problem.str();
#else
                    throw ValidationError(problem.str());
#endif
                };
 
                for (Base *child: Children())
                {
                    if (child->IsGroup() && !child->Matched())
                    {
                        onValidationError();
                    }
 
                    child->Validate(shortprefix, longprefix);
                }
 
                if (subparser != nullptr)
                {
                    subparser->Validate(shortprefix, longprefix);
                    if (!subparser->Matched())
                    {
                        onValidationError();
                    }
                }
 
                if (selectedCommand == nullptr && commandIsRequired && (Group::HasCommand() || subparserHasCommand))
                {
                    std::ostringstream problem;
                    problem << "Command is required";
#ifdef ARGS_NOEXCEPT
                    error = Error::Validation;
                    errorMsg = problem.str();
#else
                    throw ValidationError(problem.str());
#endif
                }
            }
 
            virtual void Reset() noexcept override
            {
                Group::Reset();
                selectedCommand = nullptr;
                subparserProgramLine.clear();
                subparserDescription.clear();
                subparserHasFlag = false;
                subparserHasPositional = false;
                subparserHasCommand = false;
#ifdef ARGS_NOEXCEPT
                subparserError = Error::None;
#endif
            }
 
#ifdef ARGS_NOEXCEPT
            virtual Error GetError() const override
            {
                if (!Matched())
                {
                    return Error::None;
                }
 
                if (error != Error::None)
                {
                    return error;
                }
 
                if (subparserError != Error::None)
                {
                    return subparserError;
                }
 
                return Group::GetError();
            }
#endif
    };
 
    class ArgumentParser : public Command
    {
        friend class Subparser;
 
        private:
            std::string longprefix;
            std::string shortprefix;
 
            std::string longseparator;
 
            std::string terminator;
 
            bool allowJoinedShortValue = true;
            bool allowJoinedLongValue = true;
            bool allowSeparateShortValue = true;
            bool allowSeparateLongValue = true;
 
            bool readCompletion = false;
            CompletionFlag *completion = nullptr;
 
        protected:
            enum class OptionType
            {
                LongFlag,
                ShortFlag,
                Positional
            };
 
            OptionType ParseOption(const std::string &s, bool allowEmpty = false)
            {
                const bool matchesLong = s.find(longprefix) == 0 && (allowEmpty || s.length() > longprefix.length());
                const bool matchesShort = s.find(shortprefix) == 0 && (allowEmpty || s.length() > shortprefix.length());
 
                // A chunk can start with both prefixes when one is a prefix of
                // the other, or when the long prefix is empty (every string
                // starts with it). Resolve to the longer, more specific prefix:
                // this keeps the default "--"/"-" preference for long flags
                // while letting a short flag be recognised under an empty long
                // prefix instead of being swallowed as a nameless long flag.
                if (matchesLong && matchesShort)
                {
                    return longprefix.length() >= shortprefix.length() ? OptionType::LongFlag : OptionType::ShortFlag;
                }
 
                if (matchesLong)
                {
                    return OptionType::LongFlag;
                }
 
                if (matchesShort)
                {
                    return OptionType::ShortFlag;
                }
 
                return OptionType::Positional;
            }
 
            template <typename It>
            bool Complete(FlagBase &flag, It it, It end)
            {
                auto nextIt = it;
                if (!readCompletion || (++nextIt != end))
                {
                    return false;
                }
 
                const auto &chunk = *it;
                for (auto &choice : flag.HelpChoices(helpParams))
                {
                    AddCompletionReply(chunk, choice);
                }
 
#ifndef ARGS_NOEXCEPT
                throw Completion(completion->Get());
#else
                return true;
#endif
            }
 
            template <typename It>
            std::string ParseArgsValues(FlagBase &flag, const std::string &arg, It &it, It end,
                                        const bool allowSeparate, const bool allowJoined,
                                        const bool hasJoined, const std::string &joinedArg,
                                        const bool canDiscardJoined, std::vector<std::string> &values)
            {
                values.clear();
 
                Nargs nargs = flag.NumberOfArguments();
 
                if (hasJoined && !allowJoined && (nargs.min != 0 || !canDiscardJoined))
                {
                    return "Flag '" + arg + "' was passed a joined argument, but these are disallowed";
                }
 
                if (hasJoined)
                {
                    if (!canDiscardJoined || (allowJoined && nargs.max != 0))
                    {
                        values.push_back(joinedArg);
                    }
                } else if (!allowSeparate)
                {
                    if (nargs.min != 0)
                    {
                        return "Flag '" + arg + "' was passed a separate argument, but these are disallowed";
                    }
                } else if (allowSeparate && (!hasJoined || !values.empty())) {
                    // Only gather separate values when they are allowed. A joined
                    // value that was discarded rather than taken (short chunks such
                    // as -nf when joined short values are off) means this flag isn't
                    // taking an argument here, so the rest of the chunk is flags.
                    auto valueIt = it;
                    ++valueIt;
 
                    while (valueIt != end &&
                           *valueIt != terminator &&
                           values.size() < nargs.max &&
                           (values.size() < nargs.min || ParseOption(*valueIt) == OptionType::Positional))
                    {
                        if (Complete(flag, valueIt, end))
                        {
                            // Park `it` on the completion position rather than
                            // `end`. In ARGS_NOEXCEPT mode Complete returns
                            // true (no throw), so the caller's for-loop will
                            // run its ++it after we return; advancing an
                            // already-end iterator is undefined behavior and
                            // causes a subsequent out-of-bounds read of the
                            // arg vector. Since Complete only fires when
                            // ++nextIt == end, valueIt is the last element,
                            // and ++(it=valueIt) safely lands on end.
                            it = valueIt;
                            return "";
                        }
 
                        values.push_back(*valueIt);
                        ++it;
                        ++valueIt;
                    }
                }
 
                if (values.size() > nargs.max)
                {
                    return "Passed an argument into a non-argument flag: " + arg;
                } else if (values.size() < nargs.min)
                {
                    if (nargs.min == 1 && nargs.max == 1)
                    {
                        return "Flag '" + arg + "' requires an argument but received none";
                    } else if (nargs.min == 1)
                    {
                        return "Flag '" + arg + "' requires at least one argument but received none";
                    } else if (nargs.min != nargs.max)
                    {
                        return "Flag '" + arg + "' requires at least " + std::to_string(nargs.min) +
                               " arguments but received " + std::to_string(values.size());
                    } else
                    {
                        return "Flag '" + arg + "' requires " + std::to_string(nargs.min) +
                               " arguments but received " + std::to_string(values.size());
                    }
                }
 
                return {};
            }
 
            template <typename It>
            bool ParseLong(It &it, It end)
            {
                const auto &chunk = *it;
                const auto argchunk = chunk.substr(longprefix.size());
                // Try to separate it, in case of a separator:
                const auto separator = longseparator.empty() ? argchunk.npos : argchunk.find(longseparator);
                // If the separator is in the argument, separate it.
                const auto arg = (separator != argchunk.npos ?
                    std::string(argchunk, 0, separator)
                    : argchunk);
                const auto joined = (separator != argchunk.npos ?
                    argchunk.substr(separator + longseparator.size())
                    : std::string());
 
                if (auto flag = Match(arg))
                {
#ifdef ARGS_NOEXCEPT
                    // Match() may set the flag's error (e.g. Error::Extra when
                    // Options::Single is violated). In non-noexcept mode that
                    // path throws and parsing stops before the value is read;
                    // in noexcept mode we must mirror that and skip the value
                    // parsing so the previously-stored value is preserved.
                    if (flag->GetError() != Error::None)
                    {
                        return false;
                    }
#endif
                    std::vector<std::string> values;
                    const std::string errorMessage = ParseArgsValues(*flag, arg, it, end, allowSeparateLongValue, allowJoinedLongValue,
                                                                     separator != argchunk.npos, joined, false, values);
                    if (!errorMessage.empty())
                    {
#ifndef ARGS_NOEXCEPT
                        throw ParseError(errorMessage);
#else
                        error = Error::Parse;
                        errorMsg = errorMessage;
                        return false;
#endif
                    }
 
                    if (!readCompletion)
                    {
                        flag->ParseValue(values);
#ifdef ARGS_NOEXCEPT
                        // Non-noexcept ParseValue paths throw on Help, reader
                        // failure, or Map miss, which halts parsing. Mirror
                        // that here so a later parser-level error (e.g. an
                        // unknown flag) cannot shadow the flag's error in
                        // ArgumentParser::GetError().
                        if (flag->GetError() != Error::None)
                        {
                            return false;
                        }
#endif
                    }
 
                    if (flag->KickOut())
                    {
                        ++it;
                        return false;
                    }
                } else
                {
                    const std::string errorMessage("Flag could not be matched: " + arg);
#ifndef ARGS_NOEXCEPT
                    throw ParseError(errorMessage);
#else
                    error = Error::Parse;
                    errorMsg = errorMessage;
                    return false;
#endif
                }
 
                return true;
            }
 
            template <typename It>
            bool ParseShort(It &it, It end)
            {
                const auto &chunk = *it;
                const auto argchunk = chunk.substr(shortprefix.size());
                for (auto argit = std::begin(argchunk); argit != std::end(argchunk); ++argit)
                {
                    const auto arg = *argit;
 
                    if (auto flag = Match(arg))
                    {
#ifdef ARGS_NOEXCEPT
                        // See ParseLong: if Match recorded an error
                        // (e.g. Options::Single violation), bail before the
                        // value is parsed so the prior value is preserved.
                        if (flag->GetError() != Error::None)
                        {
                            return false;
                        }
#endif
                        const std::string value(argit + 1, std::end(argchunk));
                        std::vector<std::string> values;
                        const std::string errorMessage = ParseArgsValues(*flag, std::string(1, arg), it, end,
                                                                         allowSeparateShortValue, allowJoinedShortValue,
                                                                         !value.empty(), value, !value.empty(), values);
 
                        if (!errorMessage.empty())
                        {
#ifndef ARGS_NOEXCEPT
                            throw ParseError(errorMessage);
#else
                            error = Error::Parse;
                            errorMsg = errorMessage;
                            return false;
#endif
                        }
 
                        if (!readCompletion)
                        {
                            flag->ParseValue(values);
#ifdef ARGS_NOEXCEPT
                            // See ParseLong: ensure a flag-level error from
                            // ParseValue (Help, Parse, Map) halts parsing so
                            // it cannot be shadowed by a later parser error.
                            if (flag->GetError() != Error::None)
                            {
                                return false;
                            }
#endif
                        }
 
                        if (flag->KickOut())
                        {
                            ++it;
                            return false;
                        }
 
                        if (!values.empty())
                        {
                            break;
                        }
                    } else
                    {
                        const std::string errorMessage("Flag could not be matched: '" + std::string(1, arg) + "'");
#ifndef ARGS_NOEXCEPT
                        throw ParseError(errorMessage);
#else
                        error = Error::Parse;
                        errorMsg = errorMessage;
                        return false;
#endif
                    }
                }
 
                return true;
            }
 
            bool AddCompletionReply(const std::string &cur, const std::string &choice)
            {
                if (cur.empty() || choice.find(cur) == 0)
                {
                    if (completion->syntax == "bash" && ParseOption(choice) == OptionType::LongFlag && choice.find(longseparator) != std::string::npos)
                    {
                        completion->reply.push_back(choice.substr(choice.find(longseparator) + longseparator.size()));
                    } else
                    {
                        completion->reply.push_back(choice);
                    }
                    return true;
                }
 
                return false;
            }
 
            template <typename It>
            bool Complete(It it, It end, bool terminated)
            {
                auto nextIt = it;
                if (!readCompletion || (++nextIt != end))
                {
                    return false;
                }
 
                const auto &chunk = *it;
                auto pos = GetNextPositional();
                std::vector<Command *> commands = GetCommands();
                const auto optionType = ParseOption(chunk, true);
 
                // Once the terminator has been seen the parser treats every
                // following chunk as positional, so only positional choices are
                // valid completions here. Suggesting flags or commands past the
                // terminator offers candidates the parser would then reject.
                if (!terminated && !commands.empty() && (chunk.empty() || optionType == OptionType::Positional))
                {
                    for (auto &cmd : commands)
                    {
                        if ((cmd->GetOptions() & Options::HiddenFromCompletion) == Options::None)
                        {
                            AddCompletionReply(chunk, cmd->Name());
                        }
                    }
                } else
                {
                    bool hasPositionalCompletion = true;
 
                    if (!terminated && !commands.empty())
                    {
                        for (auto &cmd : commands)
                        {
                            if ((cmd->GetOptions() & Options::HiddenFromCompletion) == Options::None)
                            {
                                AddCompletionReply(chunk, cmd->Name());
                            }
                        }
                    } else if (pos)
                    {
                        if ((pos->GetOptions() & Options::HiddenFromCompletion) == Options::None)
                        {
                            auto choices = pos->HelpChoices(helpParams);
                            hasPositionalCompletion = !choices.empty() || optionType != OptionType::Positional;
                            for (auto &choice : choices)
                            {
                                AddCompletionReply(chunk, choice);
                            }
                        }
                    }
 
                    if (!terminated && hasPositionalCompletion)
                    {
                        auto flags = GetAllFlags();
                        for (auto flag : flags)
                        {
                            if ((flag->GetOptions() & Options::HiddenFromCompletion) != Options::None)
                            {
                                continue;
                            }
 
                            auto &matcher = flag->GetMatcher();
                            if (!AddCompletionReply(chunk, matcher.GetShortOrAny().str(shortprefix, longprefix)))
                            {
                                for (auto &flagName : matcher.GetFlagStrings())
                                {
                                    if (AddCompletionReply(chunk, flagName.str(shortprefix, longprefix)))
                                    {
                                        break;
                                    }
                                }
                            }
                        }
 
                        if (optionType == OptionType::LongFlag && allowJoinedLongValue)
                        {
                            const auto separator = longseparator.empty() ? chunk.npos : chunk.find(longseparator);
                            // Only attempt joined-value completion when the
                            // separator lies at or past the long prefix, so
                            // there is a (possibly empty) flag name between
                            // them. With a custom longseparator that overlaps
                            // the prefix (e.g. LongSeparator("-") under the
                            // default "--" prefix), an attacker-controlled
                            // completion word like "--x" puts the separator
                            // inside the prefix, making `arg` shorter than
                            // longprefix. arg.substr(longprefix.size()) would
                            // then throw std::out_of_range, which escapes the
                            // parser as a non-args exception (bypassing the
                            // documented catch(args::Error) idiom) and is
                            // thrown even under ARGS_NOEXCEPT.
                            if (separator != chunk.npos && separator >= longprefix.size())
                            {
                                std::string arg(chunk, 0, separator);
                                if (auto flag = this->Match(arg.substr(longprefix.size())))
                                {
                                    for (auto &choice : flag->HelpChoices(helpParams))
                                    {
                                        AddCompletionReply(chunk, arg + longseparator + choice);
                                    }
                                }
                            }
                        } else if (optionType == OptionType::ShortFlag && allowJoinedShortValue)
                        {
                            if (chunk.size() > shortprefix.size() + 1)
                            {
                                auto arg = chunk.at(shortprefix.size());
                                //TODO: support -abcVALUE where a and b take no value
                                if (auto flag = this->Match(arg))
                                {
                                    for (auto &choice : flag->HelpChoices(helpParams))
                                    {
                                        AddCompletionReply(chunk, shortprefix + arg + choice);
                                    }
                                }
                            }
                        }
                    }
                }
 
#ifndef ARGS_NOEXCEPT
                throw Completion(completion->Get());
#else
                return true;
#endif
            }
 
            template <typename It>
            It Parse(It begin, It end)
            {
                bool terminated = false;
                std::vector<Command *> commands = GetCommands();
 
                // Check all arg chunks
                for (auto it = begin; it != end; ++it)
                {
                    if (Complete(it, end, terminated))
                    {
                        return end;
                    }
 
                    const auto &chunk = *it;
 
                    if (!terminated && chunk == terminator)
                    {
                        terminated = true;
                    } else if (!terminated && ParseOption(chunk) == OptionType::LongFlag)
                    {
                        if (!ParseLong(it, end))
                        {
                            return it;
                        }
                    } else if (!terminated && ParseOption(chunk) == OptionType::ShortFlag)
                    {
                        if (!ParseShort(it, end))
                        {
                            return it;
                        }
                    } else if (!terminated && !commands.empty())
                    {
                        auto itCommand = std::find_if(commands.begin(), commands.end(), [&chunk](Command *c) { return c->Name() == chunk; });
                        if (itCommand == commands.end())
                        {
                            const std::string errorMessage("Unknown command: " + chunk);
#ifndef ARGS_NOEXCEPT
                            throw ParseError(errorMessage);
#else
                            error = Error::Parse;
                            errorMsg = errorMessage;
                            return it;
#endif
                        }
 
                        SelectCommand(*itCommand);
 
                        if (const auto &coroutine = GetCoroutine())
                        {
                            ++it;
                            RaiiSubparser coro(*this, std::vector<std::string>(it, end));
                            coroutine(coro.Parser());
#ifdef ARGS_NOEXCEPT
                            error = GetError();
                            if (error != Error::None)
                            {
                                return end;
                            }
 
                            if (!coro.Parser().IsParsed())
                            {
                                error = Error::Usage;
                                return end;
                            }
#else
                            if (!coro.Parser().IsParsed())
                            {
                                throw UsageError("Subparser::Parse was not called");
                            }
#endif
 
                            break;
                        }
 
                        commands = GetCommands();
                    } else
                    {
                        auto pos = GetNextPositional();
                        if (pos)
                        {
                            pos->ParseValue(chunk);
#ifdef ARGS_NOEXCEPT
                            if (pos->GetError() != Error::None)
                            {
                                return it;
                            }
#endif
 
                            if (pos->KickOut())
                            {
                                return ++it;
                            }
                        } else
                        {
                            const std::string errorMessage("Passed in argument, but no positional arguments were ready to receive it: " + chunk);
#ifndef ARGS_NOEXCEPT
                            throw ParseError(errorMessage);
#else
                            error = Error::Parse;
                            errorMsg = errorMessage;
                            return it;
#endif
                        }
                    }
 
                    if (!readCompletion && completion != nullptr && completion->Matched())
                    {
#ifdef ARGS_NOEXCEPT
                        if (completion->GetError() != Error::None)
                        {
                            error = completion->GetError();
                            if (errorMsg.empty())
                            {
                                errorMsg = completion->GetErrorMsg();
                            }
                            return it;
                        }
 
                        error = Error::Completion;
#endif
                        readCompletion = true;
                        ++it;
                        const auto argsLeft = static_cast<size_t>(std::distance(it, end));
                        if (completion->cword == 0 || argsLeft <= 1 || completion->cword >= argsLeft)
                        {
#ifndef ARGS_NOEXCEPT
                            throw Completion("");
#else
                            return end;
#endif
                        }
 
                        ++it;
                        std::vector<std::string> curArgs;
                        curArgs.reserve(completion->cword);
                        auto curIt = it;
                        for (size_t idx = 0; idx < completion->cword && curIt != end; ++idx, ++curIt)
                        {
                            curArgs.push_back(*curIt);
                        }
 
                        if (completion->syntax == "bash")
                        {
                            // bash tokenizes --flag=value as --flag=value
                            // Security fix: Use size_t arithmetic throughout to avoid conversion issues
                            for (size_t idx = 0; idx < curArgs.size(); )
                            {
                                if (idx > 0 && curArgs[idx] == "=")
                                {
                                    size_t prev_idx = idx - 1;  // Safe since we checked idx > 0
                                    curArgs[prev_idx] += "=";
                                    size_t next_idx = 0;
                                    if (SafeAdd<size_t>(idx, static_cast<size_t>(1), next_idx) && next_idx < curArgs.size())
                                    {
                                        curArgs[prev_idx] += curArgs[next_idx];
                                        // Erase the '=' token and the following value token.
                                        size_t erase_end = 0;
                                        if (SafeAdd<size_t>(next_idx, static_cast<size_t>(1), erase_end))
                                        {
                                            typedef std::vector<std::string>::difference_type diff_t;
                                            curArgs.erase(curArgs.begin() + static_cast<diff_t>(idx),
                                                         curArgs.begin() + static_cast<diff_t>(erase_end));
                                        }
                                    } else
                                    {
                                        // Safe erase of single '=' token at the end
                                        typedef std::vector<std::string>::difference_type diff_t;
                                        curArgs.erase(curArgs.begin() + static_cast<diff_t>(idx));
                                    }
                                    // Do not increment idx - next element slides into current position
                                } else
                                {
                                    ++idx;
                                }
                            }
 
                        }
#ifndef ARGS_NOEXCEPT
                        try
                        {
                            Parse(curArgs.begin(), curArgs.end());
                            throw Completion("");
                        }
                        catch (Completion &)
                        {
                            throw;
                        }
                        catch (args::Error&)
                        {
                            throw Completion("");
                        }
#else
                        // Discard the nested Parse's return value: it points
                        // into the local curArgs vector, which is destroyed
                        // when this function returns, leaving the caller with
                        // a dangling iterator that would be compared against
                        // the outer `end` in ParseCLI. Return the outer
                        // `end` instead so the iterator stays in the caller's
                        // container.
                        Parse(curArgs.begin(), curArgs.end());
                        error = Error::Completion;
                        errorMsg.clear();
                        return end;
#endif
                    }
                }
 
                Validate(shortprefix, longprefix);
                return end;
            }
 
        public:
            HelpParams helpParams;
 
            ArgumentParser(const std::string &description_, const std::string &epilog_ = std::string())
            {
                Description(description_);
                Epilog(epilog_);
                LongPrefix("--");
                ShortPrefix("-");
                LongSeparator("=");
                Terminator("--");
                SetArgumentSeparations(true, true, true, true);
                matched = true;
            }
 
            void AddCompletion(CompletionFlag &completionFlag)
            {
                // Only take the pointer once registration has succeeded: Add()
                // throws on a duplicate flag, and the flag it was handed is
                // gone by the time that error reaches the caller.
                Add(completionFlag);
                completion = &completionFlag;
            }
 
            const std::string &Prog() const
            { return helpParams.programName; }
            void Prog(const std::string &prog_)
            { this->helpParams.programName = prog_; }
 
            const std::string &LongPrefix() const
            { return longprefix; }
            void LongPrefix(const std::string &longprefix_)
            {
                this->longprefix = longprefix_;
                this->helpParams.longPrefix = longprefix_;
            }
 
            const std::string &ShortPrefix() const
            { return shortprefix; }
            void ShortPrefix(const std::string &shortprefix_)
            {
                this->shortprefix = shortprefix_;
                this->helpParams.shortPrefix = shortprefix_;
            }
 
            const std::string &LongSeparator() const
            { return longseparator; }
            void LongSeparator(const std::string &longseparator_)
            {
                if (longseparator_.empty())
                {
                    const std::string errorMessage("longseparator can not be set to empty");
#ifdef ARGS_NOEXCEPT
                    error = Error::Usage;
                    errorMsg = errorMessage;
#else
                    throw UsageError(errorMessage);
#endif
                } else
                {
                    this->longseparator = longseparator_;
                    this->helpParams.longSeparator = allowJoinedLongValue ? longseparator : " ";
                }
            }
 
            const std::string &Terminator() const
            { return terminator; }
            void Terminator(const std::string &terminator_)
            { this->terminator = terminator_; }
 
            void GetArgumentSeparations(
                bool &allowJoinedShortValue_,
                bool &allowJoinedLongValue_,
                bool &allowSeparateShortValue_,
                bool &allowSeparateLongValue_) const
            {
                allowJoinedShortValue_ = this->allowJoinedShortValue;
                allowJoinedLongValue_ = this->allowJoinedLongValue;
                allowSeparateShortValue_ = this->allowSeparateShortValue;
                allowSeparateLongValue_ = this->allowSeparateLongValue;
            }
 
            void SetArgumentSeparations(
                const bool allowJoinedShortValue_,
                const bool allowJoinedLongValue_,
                const bool allowSeparateShortValue_,
                const bool allowSeparateLongValue_)
            {
                this->allowJoinedShortValue = allowJoinedShortValue_;
                this->allowJoinedLongValue = allowJoinedLongValue_;
                this->allowSeparateShortValue = allowSeparateShortValue_;
                this->allowSeparateLongValue = allowSeparateLongValue_;
 
                this->helpParams.longSeparator = allowJoinedLongValue ? longseparator : " ";
                this->helpParams.shortSeparator = allowJoinedShortValue ? "" : " ";
            }
 
            void Help(std::ostream &help_) const
            {
                auto &command = SelectedCommand();
                const auto &commandDescription = command.Description().empty() ? command.Help() : command.Description();
                const auto desc_indent = helpParams.descriptionindent;
                const auto effective_desc_width = (helpParams.width > desc_indent) ? helpParams.width - desc_indent : 0;
                const auto description_text = Wrap(commandDescription, effective_desc_width);
                const auto epilog_text = Wrap(command.Epilog(), effective_desc_width);
 
                const bool hasoptions = command.HasFlag();
                const bool hasarguments = command.HasPositional();
 
                std::vector<std::string> prognameline;
                prognameline.push_back(helpParams.usageString);
                prognameline.push_back(Prog());
                auto commandProgLine = command.GetProgramLine(helpParams);
                prognameline.insert(prognameline.end(), commandProgLine.begin(), commandProgLine.end());
 
                const auto prog_sum = helpParams.progindent + helpParams.progtailindent;
                const auto effective_prog_width = (helpParams.width > prog_sum) ? helpParams.width - prog_sum : 0;
                const auto effective_prog_first = (helpParams.width > helpParams.progindent) ? helpParams.width - helpParams.progindent : 0;
                const auto proglines = Wrap(prognameline.begin(), prognameline.end(),
                                            effective_prog_width,
                                            effective_prog_first);
                auto progit = std::begin(proglines);
                if (progit != std::end(proglines))
                {
                    help_ << std::string(helpParams.progindent, ' ') << *progit << '\n';
                    ++progit;
                }
                for (; progit != std::end(proglines); ++progit)
                {
                    help_ << std::string(helpParams.progtailindent, ' ') << *progit << '\n';
                }
 
                help_ << '\n';
 
                if (!description_text.empty())
                {
                    for (const auto &line: description_text)
                    {
                        help_ << std::string(helpParams.descriptionindent, ' ') << line << "\n";
                    }
                    help_ << "\n";
                }
 
                bool lastDescriptionIsNewline = false;
 
                if (!helpParams.optionsString.empty())
                {
                    help_ << std::string(helpParams.progindent, ' ') << helpParams.optionsString << "\n\n";
                }
 
                for (const auto &desc: command.GetDescription(helpParams, 0))
                {
                    lastDescriptionIsNewline = std::get<0>(desc).empty() && std::get<1>(desc).empty();
                    const auto groupindent = std::get<2>(desc) * helpParams.eachgroupindent;
                    const auto flag_sum = helpParams.flagindent + helpParams.helpindent + helpParams.gutter;
                    const auto effective_flag_width = (helpParams.width > flag_sum) ? helpParams.width - flag_sum : 0;
                    const auto flags = Wrap(std::get<0>(desc), effective_flag_width);
                    const auto info_sum = helpParams.helpindent + groupindent;
                    const auto effective_info_width = (helpParams.width > info_sum) ? helpParams.width - info_sum : 0;
                    const auto info = Wrap(std::get<1>(desc), effective_info_width);
 
                    std::string::size_type flagssize = 0;
                    for (auto flagsit = std::begin(flags); flagsit != std::end(flags); ++flagsit)
                    {
                        if (flagsit != std::begin(flags))
                        {
                            help_ << '\n';
                        }
                        help_ << std::string(groupindent + helpParams.flagindent, ' ') << *flagsit;
                        flagssize = Glyphs(*flagsit);
                    }
 
                    auto infoit = std::begin(info);
                    // groupindent is on both sides of this inequality, and therefore can be removed
                    if ((helpParams.flagindent + flagssize + helpParams.gutter) > helpParams.helpindent || infoit == std::end(info) || helpParams.addNewlineBeforeDescription)
                    {
                        help_ << '\n';
                    } else
                    {
                        // groupindent is on both sides of the minus sign, and therefore doesn't actually need to be in here
                        const auto indent_sum = helpParams.flagindent + flagssize;
                        const auto effective_space = (helpParams.helpindent > indent_sum) ? helpParams.helpindent - indent_sum : 0;
                        help_ << std::string(effective_space, ' ') << *infoit << '\n';
                        ++infoit;
                    }
                    for (; infoit != std::end(info); ++infoit)
                    {
                        help_ << std::string(groupindent + helpParams.helpindent, ' ') << *infoit << '\n';
                    }
                }
                if (hasoptions && hasarguments && helpParams.showTerminator)
                {
                    lastDescriptionIsNewline = false;
                    const auto effective_term_width = (helpParams.width > helpParams.flagindent) ? helpParams.width - helpParams.flagindent : 0;
                    for (const auto &item: Wrap(std::string("\"") + terminator + "\" can be used to terminate flag options and force all following arguments to be treated as positional options", effective_term_width))
                    {
                        help_ << std::string(helpParams.flagindent, ' ') << item << '\n';
                    }
                }
 
                if (!lastDescriptionIsNewline)
                {
                    help_ << "\n";
                }
 
                for (const auto &line: epilog_text)
                {
                    help_ << std::string(helpParams.descriptionindent, ' ') << line << "\n";
                }
            }
 
            std::string Help() const
            {
                std::ostringstream help_;
                Help(help_);
                return help_.str();
            }
 
            virtual void Reset() noexcept override
            {
                Command::Reset();
                matched = true;
                readCompletion = false;
            }
 
            template <typename It>
            It ParseArgs(It begin, It end)
            {
                // Reset all Matched statuses and errors
                Reset();
#ifdef ARGS_NOEXCEPT
                error = GetError();
                if (error != Error::None)
                {
                    return end;
                }
#endif
                return Parse(begin, end);
            }
 
            template <typename T>
            auto ParseArgs(const T &args) -> decltype(std::begin(args))
            {
                return ParseArgs(std::begin(args), std::end(args));
            }
 
            bool ParseCLI(const int argc, const char * const * argv)
            {
                if (argc > 0 && argv != nullptr && argv[0] != nullptr && Prog().empty())
                {
                    Prog(argv[0]);
                }
 
                std::vector<std::string> args;
                if (argc > 1 && argv != nullptr)
                {
                    args.assign(argv + 1, argv + argc);
                }
 
                return ParseArgs(args) == std::end(args);
            }
            
            template <typename T>
            bool ParseCLI(const T &args)
            {
                return ParseArgs(args) == std::end(args);
            }
    };
 
    inline Command::RaiiSubparser::RaiiSubparser(ArgumentParser &parser_, std::vector<std::string> args_)
        : command(parser_.SelectedCommand()), parser(std::move(args_), parser_, command, parser_.helpParams), oldSubparser(command.subparser)
    {
        command.subparser = &parser;
    }
 
    inline Command::RaiiSubparser::RaiiSubparser(const Command &command_, const HelpParams &params_): command(command_), parser(command, params_), oldSubparser(command.subparser)
    {
        command.subparser = &parser;
    }
 
    inline void Subparser::Parse()
    {
        isParsed = true;
        Reset();
        command.subparserDescription = GetDescription(helpParams, 0);
        command.subparserHasFlag = HasFlag();
        command.subparserHasPositional = HasPositional();
        command.subparserHasCommand = HasCommand();
        command.subparserProgramLine = GetProgramLine(helpParams);
        if (parser == nullptr)
        {
#ifndef ARGS_NOEXCEPT
            throw args::SubparserError();
#else
            error = Error::Subparser;
            return;
#endif
        }
 
        auto it = parser->Parse(args.begin(), args.end());
        command.Validate(parser->ShortPrefix(), parser->LongPrefix());
        kicked.assign(it, args.end());
 
#ifdef ARGS_NOEXCEPT
        command.subparserError = GetError();
#endif
    }
 
    inline std::ostream &operator<<(std::ostream &os, const ArgumentParser &parser)
    {
        parser.Help(os);
        return os;
    }
 
    class Flag : public FlagBase
    {
        public:
            Flag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, Options options_): FlagBase(name_, help_, std::move(matcher_), options_)
            {
                group_.Add(*this);
            }
 
            Flag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const bool extraError_ = false): Flag(group_, name_, help_, std::move(matcher_), extraError_ ? Options::Single : Options::None)
            {
            }
 
            virtual ~Flag() {}
 
            bool Get() const
            {
                return Matched();
            }
 
            virtual Nargs NumberOfArguments() const noexcept override
            {
                return 0;
            }
 
            virtual void ParseValue(const std::vector<std::string>&) override
            {
            }
    };
 
    class HelpFlag : public Flag
    {
        public:
            HelpFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, Options options_ = {}): Flag(group_, name_, help_, std::move(matcher_), options_) {}
 
            virtual ~HelpFlag() {}
 
            virtual void ParseValue(const std::vector<std::string> &)
            {
#ifdef ARGS_NOEXCEPT
                    error = Error::Help;
                    errorMsg = Name();
#else
                    throw Help(Name());
#endif
            }
 
            bool Get() const noexcept
            {
                return Matched();
            }
    };
 
    class CounterFlag : public Flag
    {
        private:
            const int startcount;
            int count;
 
        public:
            CounterFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const int startcount_ = 0, Options options_ = {}):
                Flag(group_, name_, help_, std::move(matcher_), options_), startcount(startcount_), count(startcount_) {}
 
            virtual ~CounterFlag() {}
 
            virtual FlagBase *Match(const EitherFlag &arg) override
            {
                auto me = FlagBase::Match(arg);
                if (me)
                {
#ifdef ARGS_NOEXCEPT
                    // Suppress increment when FlagBase::Match recorded an
                    // error on this same call (e.g. Options::Single violated).
                    // In non-noexcept mode that path would have thrown before
                    // reaching here and the count would not have advanced.
                    if (GetError() != Error::None)
                    {
                        return me;
                    }
#endif
                    ++count;
                }
                return me;
            }
 
            int &Get() noexcept
            {
                return count;
            }
 
            int &operator *() noexcept {
                return count;
            }
            
            const int &operator *() const noexcept {
                return count;
            }
 
            virtual void Reset() noexcept override
            {
                FlagBase::Reset();
                count = startcount;
            }
    };
 
    class ActionFlag : public FlagBase
    {
        private:
            std::function<void(const std::vector<std::string> &)> action;
            Nargs nargs;
 
        public:
            ActionFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, Nargs nargs_, std::function<void(const std::vector<std::string> &)> action_, Options options_ = {}):
                FlagBase(name_, help_, std::move(matcher_), options_), action(std::move(action_)), nargs(nargs_)
            {
                group_.Add(*this);
            }
 
            ActionFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, std::function<void(const std::string &)> action_, Options options_ = {}):
                FlagBase(name_, help_, std::move(matcher_), options_), nargs(1)
            {
                group_.Add(*this);
                action = [action_](const std::vector<std::string> &a) { return action_(a.at(0)); };
            }
 
            ActionFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, std::function<void()> action_, Options options_ = {}):
                FlagBase(name_, help_, std::move(matcher_), options_), nargs(0)
            {
                group_.Add(*this);
                action = [action_](const std::vector<std::string> &) { return action_(); };
            }
 
            virtual Nargs NumberOfArguments() const noexcept override
            { return nargs; }
 
            virtual void ParseValue(const std::vector<std::string> &value) override
            { action(value); }
    };
 
    struct ValueReader
    {
      private:
        template <typename T>
        static typename std::enable_if<std::is_integral<T>::value && std::is_unsigned<T>::value, bool>::type
        HasUnsignedNegativeSign(const std::string &value)
        {
            const auto firstNonSpace = std::find_if_not(value.begin(), value.end(), [](char c)
            {
                return std::isspace(static_cast<unsigned char>(c)) != 0;
            });
 
            return firstNonSpace != value.end() && *firstNonSpace == '-';
        }
 
        template <typename T>
        static typename std::enable_if<!std::is_integral<T>::value || !std::is_unsigned<T>::value, bool>::type
        HasUnsignedNegativeSign(const std::string &)
        {
            return false;
        }
 
      public:
        template <typename T>
        typename std::enable_if<
            std::is_integral<T>::value &&
            !std::is_same<T, bool>::value &&
            !std::is_same<T, char>::value &&
            !std::is_same<T, signed char>::value &&
            !std::is_same<T, unsigned char>::value,
            bool>::type
        ParseNumericValue(const std::string &value, T &destination)
        {
            if (HasUnsignedNegativeSign<T>(value))
            {
                return false;
            }
 
            const char *begin = value.c_str();
            // The true end of the value, derived from its length rather than
            // from the first NUL. strtoull/strtoll treat the buffer as a C
            // string and stop at an embedded '\0', so checking `*end == '\0'`
            // for "no trailing data" is defeated by a value like "12\0junk":
            // end lands on the embedded NUL and the junk after it is silently
            // accepted. Comparing against `stop` validates the whole string
            // and matches the istringstream-based reader used for other types.
            const char *const stop = begin + value.size();
 
            // C++11-compatible: use strtoull/strtoll. Hardening retained from
            // the original from_chars draft (errno save/restore, ERANGE check,
            // narrowing range check, trailing-whitespace tolerance). No
            // unconditional dependency on <charconv> / C++17.
            const int saved_errno = errno;
            errno = 0;
 
            char *end = nullptr;
 
            if (std::is_unsigned<T>::value)
            {
                const unsigned long long parsed = std::strtoull(begin, &end, 0);
                if (end == begin)
                {
                    errno = saved_errno;
                    return false;
                }
                while (end != stop && std::isspace(static_cast<unsigned char>(*end)))
                {
                    ++end;
                }
                if (end != stop || errno == ERANGE ||
                    parsed > static_cast<unsigned long long>(std::numeric_limits<T>::max()))
                {
                    errno = saved_errno;
                    return false;
                }
 
                destination = static_cast<T>(parsed);
            }
            else
            {
                const long long parsed = std::strtoll(begin, &end, 0);
                if (end == begin)
                {
                    errno = saved_errno;
                    return false;
                }
                while (end != stop && std::isspace(static_cast<unsigned char>(*end)))
                {
                    ++end;
                }
                if (end != stop || errno == ERANGE ||
                    parsed < static_cast<long long>(std::numeric_limits<T>::min()) ||
                    parsed > static_cast<long long>(std::numeric_limits<T>::max()))
                {
                    errno = saved_errno;
                    return false;
                }
 
                destination = static_cast<T>(parsed);
            }
 
            errno = saved_errno;
            return true;
        }
 
        template <typename T>
        typename std::enable_if<
            !std::is_integral<T>::value ||
            std::is_same<T, bool>::value ||
            std::is_same<T, char>::value ||
            std::is_same<T, signed char>::value ||
            std::is_same<T, unsigned char>::value,
            bool>::type
        ParseNumericValue(const std::string &value, T &destination)
        {
            std::istringstream ss(value);
            // Pin parsing to the C locale so that the decimal separator and
            // thousands grouping behavior do not silently depend on whatever
            // std::locale::global was last set to elsewhere in the process.
            // Without this, e.g. "3.14" parses as 3 (with ".14" trailing) in
            // any locale whose numpunct facet treats ',' as the decimal point.
            ss.imbue(std::locale::classic());
            ss >> destination;
            if (ss.fail())
            {
                return false;
            }
 
            // Check for trailing garbage by attempting to extract any remaining characters.
            // Do not use 'ss >> std::ws' followed by peek(), as std::ws can set failbit
            // on EOF, causing false rejection of valid input.
            char extra = '\0';
            ss >> std::ws >> extra;
            // If extraction succeeded, there's trailing garbage (return false).
            // If extraction failed due to EOF only (goodbit after ws extraction), it's valid (return true).
            // If extraction failed for other reasons, it's invalid (return false).
            if (ss.fail())
            {
                // Clear the failbit to check if EOF is the only issue
                ss.clear(ss.rdstate() & ~std::ios::failbit);
                return ss.eof();
            }
            // Extraction succeeded, meaning there's trailing garbage
            return false;
        }
 
        template <typename T>
        typename std::enable_if<!std::is_assignable<T, std::string>::value, bool>::type
        operator ()(const std::string &name, const std::string &value, T &destination)
        {
            const bool success = ParseNumericValue(value, destination);
            if (!success)
            {
#ifdef ARGS_NOEXCEPT
                (void)name;
                return false;
#else
                std::ostringstream problem;
                problem << "Argument '" << name << "' received invalid value type '" << value << "'";
                throw ParseError(problem.str());
#endif
            }
            return true;
        }
 
        template <typename T>
        typename std::enable_if<std::is_assignable<T, std::string>::value, bool>::type
        operator()(const std::string &, const std::string &value, T &destination)
        {
            destination = value;
            return true;
        }
    };
 
    template <
        typename T,
        typename Reader = ValueReader>
    class ValueFlag : public ValueFlagBase
    {
        protected:
            T value;
            T defaultValue;
 
            virtual std::string GetDefaultString(const HelpParams&) const override
            {
                return detail::ToString(defaultValue);
            }
 
        private:
            Reader reader;
 
        public:
 
            ValueFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const T &defaultValue_, Options options_): ValueFlagBase(name_, help_, std::move(matcher_), options_), value(defaultValue_), defaultValue(defaultValue_)
            {
                group_.Add(*this);
            }
 
            ValueFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const T &defaultValue_ = T(), const bool extraError_ = false): ValueFlag(group_, name_, help_, std::move(matcher_), defaultValue_, extraError_ ? Options::Single : Options::None)
            {
            }
 
            ValueFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, Options options_): ValueFlag(group_, name_, help_, std::move(matcher_), T(), options_)
            {
            }
 
            virtual ~ValueFlag() {}
 
            virtual void ParseValue(const std::vector<std::string> &values_) override
            {
                const std::string &value_ = values_.at(0);
 
#ifdef ARGS_NOEXCEPT
                if (!reader(name, value_, this->value))
                {
                    error = Error::Parse;
                }
#else
                reader(name, value_, this->value);
#endif
            }
 
            virtual void Reset() noexcept override
            {
                ValueFlagBase::Reset();
                value = defaultValue;
            }
 
            T &Get() noexcept
            {
                return value;
            }
 
            T &operator *() noexcept
            {
                return value;
            }
 
            const T &operator *() const noexcept
            {
                return value;
            }
 
            T *operator ->() noexcept
            {
                return &value;
            }
 
            const T *operator ->() const noexcept
            {
                return &value;
            }
 
            const T &GetDefault() noexcept
            {
                return defaultValue;
            }
    };
 
    template <
        typename T,
        typename Reader = ValueReader>
    class ImplicitValueFlag : public ValueFlag<T, Reader>
    {
        protected:
            T implicitValue;
 
        public:
 
            ImplicitValueFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const T &implicitValue_, const T &defaultValue_ = T(), Options options_ = {})
                : ValueFlag<T, Reader>(group_, name_, help_, std::move(matcher_), defaultValue_, options_), implicitValue(implicitValue_)
            {
            }
 
            ImplicitValueFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const T &defaultValue_ = T(), Options options_ = {})
                : ValueFlag<T, Reader>(group_, name_, help_, std::move(matcher_), defaultValue_, options_), implicitValue(defaultValue_)
            {
            }
 
            ImplicitValueFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, Options options_)
                : ValueFlag<T, Reader>(group_, name_, help_, std::move(matcher_), {}, options_), implicitValue()
            {
            }
 
            virtual ~ImplicitValueFlag() {}
 
            virtual Nargs NumberOfArguments() const noexcept override
            {
                return {0, 1};
            }
 
            virtual void ParseValue(const std::vector<std::string> &value_) override
            {
                if (value_.empty())
                {
                    this->value = implicitValue;
                } else
                {
                    ValueFlag<T, Reader>::ParseValue(value_);
                }
            }
    };
 
    template <typename T>
    class ConstantFlag : public Flag
    {
        T value;
 
        public:
 
        ConstantFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, Options options_, const T& value_):
        Flag(group_, name_, help_, std::move(matcher_), options_),
        value(value_)
        {}
 
        ConstantFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const T& value_, bool extraError_ = false):
        Flag(group_, name_, help_, std::move(matcher_), extraError_),
        value(value_)
        {}
 
        T operator * () const noexcept
        {
            return value;
        }
 
        T Get() const noexcept
        {
            return value;
        }
 
        const T *operator -> () const noexcept
        {
            return &value;
        }
    };
 
    template <
        typename T,
        template <typename...> class List = detail::vector,
        typename Reader = ValueReader>
    class NargsValueFlag : public FlagBase
    {
        protected:
 
            List<T> values;
            const List<T> defaultValues;
            Nargs nargs;
            Reader reader;
 
        public:
 
            typedef List<T> Container;
            typedef T value_type;
            typedef typename Container::allocator_type allocator_type;
            typedef typename Container::pointer pointer;
            typedef typename Container::const_pointer const_pointer;
            typedef T& reference;
            typedef const T& const_reference;
            typedef typename Container::size_type size_type;
            typedef typename Container::difference_type difference_type;
            typedef typename Container::iterator iterator;
            typedef typename Container::const_iterator const_iterator;
            typedef std::reverse_iterator<iterator> reverse_iterator;
            typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
            NargsValueFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, Nargs nargs_, const List<T> &defaultValues_ = {}, Options options_ = {})
                : FlagBase(name_, help_, std::move(matcher_), options_), values(defaultValues_), defaultValues(defaultValues_),nargs(nargs_)
            {
                group_.Add(*this);
            }
 
            virtual ~NargsValueFlag() {}
 
            virtual Nargs NumberOfArguments() const noexcept override
            {
                return nargs;
            }
 
            virtual void ParseValue(const std::vector<std::string> &values_) override
            {
                values.clear();
 
                for (const std::string &value : values_)
                {
                    T v {};
#ifdef ARGS_NOEXCEPT
                    if (!reader(name, value, v))
                    {
                        error = Error::Parse;
                        return;
                    }
#else
                    reader(name, value, v);
#endif
                    values.insert(std::end(values), v);
                }
            }
 
            List<T> &Get() noexcept
            {
                return values;
            }
 
            List<T> &operator *() noexcept
            {
                return values;
            }
 
            const List<T> &operator *() const noexcept
            {
                return values;
            }
 
            List<T> *operator ->() noexcept
            {
                return &values;
            }
 
            const List<T> *operator ->() const noexcept
            {
                return &values;
            }
 
            iterator begin() noexcept
            {
                return values.begin();
            }
 
            const_iterator begin() const noexcept
            {
                return values.begin();
            }
 
            const_iterator cbegin() const noexcept
            {
                return values.cbegin();
            }
 
            iterator end() noexcept
            {
                return values.end();
            }
 
            const_iterator end() const noexcept 
            {
                return values.end();
            }
 
            const_iterator cend() const noexcept
            {
                return values.cend();
            }
 
            virtual void Reset() noexcept override
            {
                FlagBase::Reset();
                values = defaultValues;
            }
 
            virtual FlagBase *Match(const EitherFlag &arg) override
            {
                const bool wasMatched = Matched();
                auto me = FlagBase::Match(arg);
                if (me && !wasMatched)
                {
                    values.clear();
                }
                return me;
            }
    };
 
    template <
        typename T,
        template <typename...> class List = detail::vector,
        typename Reader = ValueReader>
    class ValueFlagList : public ValueFlagBase
    {
        private:
            using Container = List<T>;
            Container values;
            const Container defaultValues;
            Reader reader;
 
        public:
 
            typedef T value_type;
            typedef typename Container::allocator_type allocator_type;
            typedef typename Container::pointer pointer;
            typedef typename Container::const_pointer const_pointer;
            typedef T& reference;
            typedef const T& const_reference;
            typedef typename Container::size_type size_type;
            typedef typename Container::difference_type difference_type;
            typedef typename Container::iterator iterator;
            typedef typename Container::const_iterator const_iterator;
            typedef std::reverse_iterator<iterator> reverse_iterator;
            typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
            ValueFlagList(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const Container &defaultValues_ = Container(), Options options_ = {}):
                ValueFlagBase(name_, help_, std::move(matcher_), options_), values(defaultValues_), defaultValues(defaultValues_)
            {
                group_.Add(*this);
            }
 
            virtual ~ValueFlagList() {}
 
            virtual void ParseValue(const std::vector<std::string> &values_) override
            {
                const std::string &value_ = values_.at(0);
 
                T v{};
#ifdef ARGS_NOEXCEPT
                if (!reader(name, value_, v))
                {
                    error = Error::Parse;
                    return;
                }
#else
                reader(name, value_, v);
#endif
                values.insert(std::end(values), v);
            }
 
            Container &Get() noexcept
            {
                return values;
            }
 
            Container &operator *() noexcept
            {
                return values;
            }
 
            const Container &operator *() const noexcept
            {
                return values;
            }
 
            Container *operator ->() noexcept
            {
                return &values;
            }
 
            const Container *operator ->() const noexcept
            {
                return &values;
            }
 
            virtual std::string Name() const override
            {
                return name + std::string("...");
            }
 
            virtual void Reset() noexcept override
            {
                ValueFlagBase::Reset();
                values = defaultValues;
            }
 
            virtual FlagBase *Match(const EitherFlag &arg) override
            {
                const bool wasMatched = Matched();
                auto me = FlagBase::Match(arg);
                if (me && !wasMatched)
                {
                    values.clear();
                }
                return me;
            }
 
            iterator begin() noexcept
            {
                return values.begin();
            }
 
            const_iterator begin() const noexcept
            {
                return values.begin();
            }
 
            const_iterator cbegin() const noexcept
            {
                return values.cbegin();
            }
 
            iterator end() noexcept
            {
                return values.end();
            }
 
            const_iterator end() const noexcept 
            {
                return values.end();
            }
 
            const_iterator cend() const noexcept
            {
                return values.cend();
            }
    };
 
    template <
        typename K,
        typename T,
        typename Reader = ValueReader,
        template <typename...> class Map = detail::unordered_map>
    class MapFlag : public ValueFlagBase
    {
        private:
            const Map<K, T> map;
            T value;
            const T defaultValue;
            Reader reader;
 
        protected:
            virtual std::vector<std::string> GetChoicesStrings(const HelpParams &) const override
            {
                return detail::MapKeysToStrings(map);
            }
 
        public:
 
            MapFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const Map<K, T> &map_, const T &defaultValue_, Options options_): ValueFlagBase(name_, help_, std::move(matcher_), options_), map(map_), value(defaultValue_), defaultValue(defaultValue_)
            {
                group_.Add(*this);
            }
 
            MapFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const Map<K, T> &map_, const T &defaultValue_ = T(), const bool extraError_ = false): MapFlag(group_, name_, help_, std::move(matcher_), map_, defaultValue_, extraError_ ? Options::Single : Options::None)
            {
            }
 
            MapFlag(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const Map<K, T> &map_, Options options_): MapFlag(group_, name_, help_, std::move(matcher_), map_, T(), options_)
            {
            }
 
            virtual ~MapFlag() {}
 
            virtual void ParseValue(const std::vector<std::string> &values_) override
            {
                const std::string &value_ = values_.at(0);
 
                K key{};
#ifdef ARGS_NOEXCEPT
                if (!reader(name, value_, key))
                {
                    error = Error::Parse;
                    return;
                }
#else
                reader(name, value_, key);
#endif
                auto it = map.find(key);
                if (it == std::end(map))
                {
                    std::ostringstream problem;
                    problem << "Could not find key '" << key << "' in map for arg '" << name << "'";
#ifdef ARGS_NOEXCEPT
                    error = Error::Map;
                    errorMsg = problem.str();
#else
                    throw MapError(problem.str());
#endif
                } else
                {
                    this->value = it->second;
                }
            }
 
            T &Get() noexcept
            {
                return value;
            }
 
            T &operator *() noexcept
            {
                return value;
            }
 
            const T &operator *() const noexcept
            {
                return value;
            }
 
            T *operator ->() noexcept
            {
                return &value;
            }
 
            const T *operator ->() const noexcept
            {
                return &value;
            }
 
            virtual void Reset() noexcept override
            {
                ValueFlagBase::Reset();
                value = defaultValue;
            }
    };
 
    template <
        typename K,
        typename T,
        template <typename...> class List = detail::vector,
        typename Reader = ValueReader,
        template <typename...> class Map = detail::unordered_map>
    class MapFlagList : public ValueFlagBase
    {
        private:
            using Container = List<T>;
            const Map<K, T> map;
            Container values;
            const Container defaultValues;
            Reader reader;
 
        protected:
            virtual std::vector<std::string> GetChoicesStrings(const HelpParams &) const override
            {
                return detail::MapKeysToStrings(map);
            }
 
        public:
            typedef T value_type;
            typedef typename Container::allocator_type allocator_type;
            typedef typename Container::pointer pointer;
            typedef typename Container::const_pointer const_pointer;
            typedef T& reference;
            typedef const T& const_reference;
            typedef typename Container::size_type size_type;
            typedef typename Container::difference_type difference_type;
            typedef typename Container::iterator iterator;
            typedef typename Container::const_iterator const_iterator;
            typedef std::reverse_iterator<iterator> reverse_iterator;
            typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
            MapFlagList(Group &group_, const std::string &name_, const std::string &help_, Matcher &&matcher_, const Map<K, T> &map_, const Container &defaultValues_ = Container(), Options options_ = {}):
                ValueFlagBase(name_, help_, std::move(matcher_), options_), map(map_), values(defaultValues_), defaultValues(defaultValues_)
            {
                group_.Add(*this);
            }
 
            virtual ~MapFlagList() {}
 
            virtual void ParseValue(const std::vector<std::string> &values_) override
            {
                const std::string &value_ = values_.at(0);
 
                K key{};
#ifdef ARGS_NOEXCEPT
                if (!reader(name, value_, key))
                {
                    error = Error::Parse;
                    return;
                }
#else
                reader(name, value_, key);
#endif
                auto it = map.find(key);
                if (it == std::end(map))
                {
                    std::ostringstream problem;
                    problem << "Could not find key '" << key << "' in map for arg '" << name << "'";
#ifdef ARGS_NOEXCEPT
                    error = Error::Map;
                    errorMsg = problem.str();
#else
                    throw MapError(problem.str());
#endif
                } else
                {
                    detail::AppendMappedValue(values, it->second, 0);
                }
            }
 
            Container &Get() noexcept
            {
                return values;
            }
 
            Container &operator *() noexcept
            {
                return values;
            }
 
            const Container &operator *() const noexcept
            {
                return values;
            }
 
            Container *operator ->() noexcept
            {
                return &values;
            }
 
            const Container *operator ->() const noexcept
            {
                return &values;
            }
 
            virtual std::string Name() const override
            {
                return name + std::string("...");
            }
 
            virtual void Reset() noexcept override
            {
                ValueFlagBase::Reset();
                values = defaultValues;
            }
 
            virtual FlagBase *Match(const EitherFlag &arg) override
            {
                const bool wasMatched = Matched();
                auto me = FlagBase::Match(arg);
                if (me && !wasMatched)
                {
                    values.clear();
                }
                return me;
            }
 
            iterator begin() noexcept
            {
                return values.begin();
            }
 
            const_iterator begin() const noexcept
            {
                return values.begin();
            }
 
            const_iterator cbegin() const noexcept
            {
                return values.cbegin();
            }
 
            iterator end() noexcept
            {
                return values.end();
            }
 
            const_iterator end() const noexcept 
            {
                return values.end();
            }
 
            const_iterator cend() const noexcept
            {
                return values.cend();
            }
    };
 
    template <
        typename T,
        typename Reader = ValueReader>
    class Positional : public PositionalBase
    {
        private:
            T value;
            const T defaultValue;
            Reader reader;
        public:
            Positional(Group &group_, const std::string &name_, const std::string &help_, const T &defaultValue_ = T(), Options options_ = {}): PositionalBase(name_, help_, options_), value(defaultValue_), defaultValue(defaultValue_)
            {
                group_.Add(*this);
            }
 
            Positional(Group &group_, const std::string &name_, const std::string &help_, Options options_): Positional(group_, name_, help_, T(), options_)
            {
            }
 
            virtual ~Positional() {}
 
            virtual void ParseValue(const std::string &value_) override
            {
#ifdef ARGS_NOEXCEPT
                if (!reader(name, value_, this->value))
                {
                    error = Error::Parse;
                    return;
                }
#else
                reader(name, value_, this->value);
#endif
                ready = false;
                matched = true;
            }
 
            T &Get() noexcept
            {
                return value;
            }
 
            T &operator *() noexcept
            {
                return value;
            }
 
            const T &operator *() const noexcept
            {
                return value;
            }
 
            T *operator ->() noexcept
            {
                return &value;
            }
 
            const T *operator ->() const noexcept
            {
                return &value;
            }
 
            virtual void Reset() noexcept override
            {
                PositionalBase::Reset();
                value = defaultValue;
            }
    };
 
    template <
        typename T,
        template <typename...> class List = detail::vector,
        typename Reader = ValueReader>
    class PositionalList : public PositionalBase
    {
        private:
            using Container = List<T>;
            Container values;
            const Container defaultValues;
            Reader reader;
 
        public:
            typedef T value_type;
            typedef typename Container::allocator_type allocator_type;
            typedef typename Container::pointer pointer;
            typedef typename Container::const_pointer const_pointer;
            typedef T& reference;
            typedef const T& const_reference;
            typedef typename Container::size_type size_type;
            typedef typename Container::difference_type difference_type;
            typedef typename Container::iterator iterator;
            typedef typename Container::const_iterator const_iterator;
            typedef std::reverse_iterator<iterator> reverse_iterator;
            typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
            PositionalList(Group &group_, const std::string &name_, const std::string &help_, const Container &defaultValues_ = Container(), Options options_ = {}): PositionalBase(name_, help_, options_), values(defaultValues_), defaultValues(defaultValues_)
            {
                group_.Add(*this);
            }
 
            PositionalList(Group &group_, const std::string &name_, const std::string &help_, Options options_): PositionalList(group_, name_, help_, {}, options_)
            {
            }
 
            virtual ~PositionalList() {}
 
            virtual void ParseValue(const std::string &value_) override
            {
                T v{};
#ifdef ARGS_NOEXCEPT
                if (!reader(name, value_, v))
                {
                    error = Error::Parse;
                    return;
                }
#else
                reader(name, value_, v);
#endif
                values.insert(std::end(values), v);
                matched = true;
            }
 
            virtual std::string Name() const override
            {
                return name + std::string("...");
            }
 
            Container &Get() noexcept
            {
                return values;
            }
 
            Container &operator *() noexcept
            {
                return values;
            }
 
            const Container &operator *() const noexcept
            {
                return values;
            }
 
            Container *operator ->() noexcept
            {
                return &values;
            }
 
            const Container *operator ->() const noexcept
            {
                return &values;
            }
 
            virtual void Reset() noexcept override
            {
                PositionalBase::Reset();
                values = defaultValues;
            }
 
            virtual PositionalBase *GetNextPositional() override
            {
                const bool wasMatched = Matched();
                auto me = PositionalBase::GetNextPositional();
                if (me && !wasMatched)
                {
                    values.clear();
                }
                return me;
            }
 
            iterator begin() noexcept
            {
                return values.begin();
            }
 
            const_iterator begin() const noexcept
            {
                return values.begin();
            }
 
            const_iterator cbegin() const noexcept
            {
                return values.cbegin();
            }
 
            iterator end() noexcept
            {
                return values.end();
            }
 
            const_iterator end() const noexcept 
            {
                return values.end();
            }
 
            const_iterator cend() const noexcept
            {
                return values.cend();
            }
    };
 
    template <
        typename K,
        typename T,
        typename Reader = ValueReader,
        template <typename...> class Map = detail::unordered_map>
    class MapPositional : public PositionalBase
    {
        private:
            const Map<K, T> map;
            T value;
            const T defaultValue;
            Reader reader;
 
        protected:
            virtual std::vector<std::string> GetChoicesStrings(const HelpParams &) const override
            {
                return detail::MapKeysToStrings(map);
            }
 
        public:
 
            MapPositional(Group &group_, const std::string &name_, const std::string &help_, const Map<K, T> &map_, const T &defaultValue_ = T(), Options options_ = {}):
                PositionalBase(name_, help_, options_), map(map_), value(defaultValue_), defaultValue(defaultValue_)
            {
                group_.Add(*this);
            }
 
            virtual ~MapPositional() {}
 
            virtual void ParseValue(const std::string &value_) override
            {
                K key{};
#ifdef ARGS_NOEXCEPT
                if (!reader(name, value_, key))
                {
                    error = Error::Parse;
                    return;
                }
#else
                reader(name, value_, key);
#endif
                auto it = map.find(key);
                if (it == std::end(map))
                {
                    std::ostringstream problem;
                    problem << "Could not find key '" << key << "' in map for arg '" << name << "'";
#ifdef ARGS_NOEXCEPT
                    error = Error::Map;
                    errorMsg = problem.str();
#else
                    throw MapError(problem.str());
#endif
                } else
                {
                    this->value = it->second;
                    ready = false;
                    matched = true;
                }
            }
 
            T &Get() noexcept
            {
                return value;
            }
 
            T &operator *() noexcept
            {
                return value;
            }
 
            const T &operator *() const noexcept
            {
                return value;
            }
 
            T *operator ->() noexcept
            {
                return &value;
            }
 
            const T *operator ->() const noexcept
            {
                return &value;
            }
 
            virtual void Reset() noexcept override
            {
                PositionalBase::Reset();
                value = defaultValue;
            }
    };
 
    template <
        typename K,
        typename T,
        template <typename...> class List = detail::vector,
        typename Reader = ValueReader,
        template <typename...> class Map = detail::unordered_map>
    class MapPositionalList : public PositionalBase
    {
        private:
            using Container = List<T>;
 
            const Map<K, T> map;
            Container values;
            const Container defaultValues;
            Reader reader;
 
        protected:
            virtual std::vector<std::string> GetChoicesStrings(const HelpParams &) const override
            {
                return detail::MapKeysToStrings(map);
            }
 
        public:
            typedef T value_type;
            typedef typename Container::allocator_type allocator_type;
            typedef typename Container::pointer pointer;
            typedef typename Container::const_pointer const_pointer;
            typedef T& reference;
            typedef const T& const_reference;
            typedef typename Container::size_type size_type;
            typedef typename Container::difference_type difference_type;
            typedef typename Container::iterator iterator;
            typedef typename Container::const_iterator const_iterator;
            typedef std::reverse_iterator<iterator> reverse_iterator;
            typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
            MapPositionalList(Group &group_, const std::string &name_, const std::string &help_, const Map<K, T> &map_, const Container &defaultValues_ = Container(), Options options_ = {}):
                PositionalBase(name_, help_, options_), map(map_), values(defaultValues_), defaultValues(defaultValues_)
            {
                group_.Add(*this);
            }
 
            virtual ~MapPositionalList() {}
 
            virtual void ParseValue(const std::string &value_) override
            {
                K key{};
#ifdef ARGS_NOEXCEPT
                if (!reader(name, value_, key))
                {
                    error = Error::Parse;
                    return;
                }
#else
                reader(name, value_, key);
#endif
                auto it = map.find(key);
                if (it == std::end(map))
                {
                    std::ostringstream problem;
                    problem << "Could not find key '" << key << "' in map for arg '" << name << "'";
#ifdef ARGS_NOEXCEPT
                    error = Error::Map;
                    errorMsg = problem.str();
#else
                    throw MapError(problem.str());
#endif
                } else
                {
                    detail::AppendMappedValue(values, it->second, 0);
                    matched = true;
                }
            }
 
            Container &Get() noexcept
            {
                return values;
            }
 
            Container &operator *() noexcept
            {
                return values;
            }
 
            const Container &operator *() const noexcept
            {
                return values;
            }
 
            Container *operator ->() noexcept
            {
                return &values;
            }
 
            const Container *operator ->() const noexcept
            {
                return &values;
            }
 
            virtual std::string Name() const override
            {
                return name + std::string("...");
            }
 
            virtual void Reset() noexcept override
            {
                PositionalBase::Reset();
                values = defaultValues;
            }
 
            virtual PositionalBase *GetNextPositional() override
            {
                const bool wasMatched = Matched();
                auto me = PositionalBase::GetNextPositional();
                if (me && !wasMatched)
                {
                    values.clear();
                }
                return me;
            }
 
            iterator begin() noexcept
            {
                return values.begin();
            }
 
            const_iterator begin() const noexcept
            {
                return values.begin();
            }
 
            const_iterator cbegin() const noexcept
            {
                return values.cbegin();
            }
 
            iterator end() noexcept
            {
                return values.end();
            }
 
            const_iterator end() const noexcept 
            {
                return values.end();
            }
 
            const_iterator cend() const noexcept
            {
                return values.cend();
            }
    };
}
 
#pragma pop_macro("min")
#pragma pop_macro("max")
#endif