identity.hpp

#ifndef SIPLASPLAS_UTILITY_IDENTITY_HPP
#define SIPLASPLAS_UTILITY_IDENTITY_HPP

#include "meta.hpp"
#include <utility>

namespace cpp
{

class Identity
{
public:
    template<typename T>
    constexpr auto operator()(T&& value) -> decltype(std::forward<T>(value)) const
    {
        return std::forward<T>(value);
    }

    template<typename T, typename Function>
    constexpr auto type(Function callback) -> decltype(callback(meta::identity<T>())) const
    {
        return callback(meta::identity<T>());
    }

    template<typename T>
    constexpr auto type() const
    {
        return meta::identity<T>();
    }
};

inline auto applyIdentity(const Identity& identity)
{
    return [identity](auto&& value)
    {
        return identity(std::forward<decltype(value)>(value));
    };
}

template<typename T, typename Identity>
constexpr auto applyIdentity(const Identity& identity) -> meta::type_t<decltype(identity.template type<T>())>;

}

#endif // SIPLASPLAS_UTILITY_IDENTITY_HPP