dropargs.h

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/**********************************************************************
 * LeechCraft - modular cross-platform feature rich internet client.
 * Copyright (C) 2006-2014  Georg Rudoy
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE or copy at https://www.boost.org/LICENSE_1_0.txt)
 **********************************************************************/
 
#pragma once
 
#include "typelist.h"
 
namespace LC
{
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 = std::result_of_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>...) -> std::result_of_t<F (InvokableArgs...)>
            {
                return F_ (std::forward<InvokableArgs> (args)...);
            }
        };
    }
 
    template<typename F>
    detail::Dropper<F> DropArgs (const F& f)
    {
        return detail::Dropper<F> { f };
    }
}
}