dropargs.h

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/**********************************************************************
 * LeechCraft - modular cross-platform feature rich internet client.
 * Copyright (C) 2006-2014  Georg Rudoy
 *
 * Boost Software License - Version 1.0 - August 17th, 2003
 *
 * Permission is hereby granted, free of charge, to any person or organization
 * obtaining a copy of the software and accompanying documentation covered by
 * this license (the "Software") to use, reproduce, display, distribute,
 * execute, and transmit the Software, and to prepare derivative works of the
 * Software, and to permit third-parties to whom the Software is furnished to
 * do so, all subject to the following:
 *
 * The copyright notices in the Software and this entire statement, including
 * the above license grant, this restriction and the following disclaimer,
 * must be included in all copies of the Software, in whole or in part, and
 * all derivative works of the Software, unless such copies or derivative
 * works are solely in the form of machine-executable object code generated by
 * a source language processor.
 *
 * 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, TITLE AND NON-INFRINGEMENT. IN NO EVENT
 * SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
 * FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 **********************************************************************/

#pragma once

#include "typelist.h"
#include "oldcppkludges.h"

namespace LeechCraft
{
namespace Util
{
    namespace detail
    {
        template<typename F, template<typename...> class List, typename... Args>
        constexpr List<Args...> GetInvokablePartImpl (int, List<Args...>, typename std::result_of<F (Args...)>::type* = nullptr)
        {
            return {};
        }

        template<typename F, template<typename...> class List>
        constexpr Typelist<> GetInvokablePartImpl (float, List<>)
        {
            return {};
        }

        template<typename F, typename List>
        struct InvokableType;

        template<typename F, template<typename...> class List, typename... Args>
        constexpr auto GetInvokablePartImpl (float, List<Args...> list) -> typename InvokableType<F, decltype (Reverse (Tail (Reverse (list))))>::RetType_t
        {
            return {};
        }

        template<typename F, typename List>
        struct InvokableType
        {
            using RetType_t = decltype (GetInvokablePartImpl<F> (0, List {}));
        };

        template<typename F, typename... Args>
        constexpr auto GetInvokablePart () -> decltype (GetInvokablePartImpl<F> (0, Typelist<Args...> {}))
        {
            return {};
        }

        template<template<typename...> class List, typename... Args>
        constexpr size_t Length (List<Args...>)
        {
            return sizeof... (Args);
        }

        template<typename T>
        struct Dumbifier
        {
            using Type_t = T;
        };

        template<typename T>
        using Dumbify = typename Dumbifier<T>::Type_t;

        template<typename F, typename List>
        struct InvokableResGetter;

        template<typename F, template<typename...> class List, typename... Args>
        struct InvokableResGetter<F, List<Args...>>
        {
            using RetType_t = ResultOf_t<F (Args...)>;
        };

        template<typename F>
        class Dropper
        {
            F F_;
        public:
            Dropper (const F& f)
            : F_ (f)
            {
            }

            template<typename... Args>
            auto operator() (Args... args) -> typename InvokableResGetter<F, decltype (GetInvokablePart<F, Args...> ())>::RetType_t
            {
                auto invokableList = GetInvokablePart<F, Args...> ();
                auto ignoreList = Drop<Length (decltype (invokableList) {})> (Typelist<Args...> {});
                return Invoke (invokableList, ignoreList, args...);
            }
        private:
            template<typename... InvokableArgs, typename... Rest>
            auto Invoke (Typelist<InvokableArgs...>, Typelist<Rest...>, Dumbify<InvokableArgs>... args, Dumbify<Rest>...) -> ResultOf_t<F (InvokableArgs...)>
            {
                return F_ (std::forward<InvokableArgs> (args)...);
            }
        };
    }

    template<typename F>
    detail::Dropper<F> DropArgs (const F& f)
    {
        return detail::Dropper<F> { f };
    }
}
}