functor.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,
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 * DEALINGS IN THE SOFTWARE.
 **********************************************************************/
 
#pragma once
 
#include <functional>
#include <optional>
#include <boost/optional.hpp>
#include "typeclassutil.h"
#include "void.h"
 
namespace LC
{
namespace Util
{
    template<typename T>
    struct InstanceFunctor
    {
        using UndefinedTag = void;
 
        template<typename F>
        using FmapResult_t = detail::ImplementationType;
 
        template<typename F>
        static FmapResult_t<F> Apply (const T& functor, const F& function);
    };
 
    namespace detail
    {
        template<typename T>
        constexpr bool IsFunctorImpl (int, typename InstanceFunctor<T>::UndefinedTag* = nullptr)
        {
            return false;
        }
 
        template<typename T>
        constexpr bool IsFunctorImpl (float)
        {
            return true;
        }
    }
 
    template<typename T>
    constexpr bool IsFunctor ()
    {
        return detail::IsFunctorImpl<T> (0);
    }
 
    template<typename T, typename F>
    using FmapResult_t = typename InstanceFunctor<T>::template FmapResult_t<F>;
 
    template<typename T, typename F, typename = std::enable_if_t<IsFunctor<T> ()>>
    FmapResult_t<T, F> Fmap (const T& functor, const F& function)
    {
        return InstanceFunctor<T>::Apply (functor, function);
    }
 
    template<typename T, typename F>
    auto operator* (const F& function, const T& functor) -> decltype (Fmap (functor, function))
    {
        return Fmap (functor, function);
    }
 
    template<typename T, typename F>
    auto operator* (const T& functor, const F& function) -> decltype (Fmap (functor, function))
    {
        return Fmap (functor, function);
    }
 
    namespace detail
    {
        template<typename T>
        struct WrapVoidResult
        {
            using Type = T;
        };
 
        template<>
        struct WrapVoidResult<void>
        {
            using Type = Void;
        };
 
        template<typename T>
        using WrapVoidResult_t = typename WrapVoidResult<T>::Type;
    }
 
    template<typename T>
    struct InstanceFunctor<boost::optional<T>>
    {
        template<typename F>
        using FmapResult_t = boost::optional<detail::WrapVoidResult_t<std::decay_t<std::result_of_t<F (T)>>>>;
 
        template<typename F>
        static FmapResult_t<F> Apply (const boost::optional<T>& t, const F& f)
        {
            if (!t)
                return {};
 
            if constexpr (std::is_same_v<FmapResult_t<F>, boost::optional<Void>>)
            {
                std::invoke (f, *t);
                return { Void {} };
            }
            else
                return { std::invoke (f, *t) };
        }
    };
 
    template<typename T>
    struct InstanceFunctor<std::optional<T>>
    {
        template<typename F>
        using FmapResult_t = std::optional<detail::WrapVoidResult_t<std::decay_t<std::result_of_t<F (T)>>>>;
 
        template<typename F>
        static FmapResult_t<F> Apply (const std::optional<T>& t, const F& f)
        {
            if (!t)
                return {};
 
            if constexpr (std::is_same_v<FmapResult_t<F>, std::optional<Void>>)
            {
                std::invoke (f, *t);
                return { Void {} };
            }
            else
                return { std::invoke (f, *t) };
        }
    };
}
}