iffl_mpl.h

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#pragma once

#include <iffl_config.h>
#include <type_traits>

namespace iffl::mpl {

template <typename... Whatever >
using void_t = std::void_t<Whatever ...>;

struct nonesuch {
    nonesuch() = delete;
    ~nonesuch() = delete;
    nonesuch(nonesuch const &) = delete;
    nonesuch const &operator=(nonesuch const &) = delete;
};

namespace details {
    template<typename Default,
             typename AlwaysVoid,
             template<typename... > typename Operation,
             typename... Arguments>
    struct detector {
        using value_type = std::false_type;
        using type = Default;
    };
    template<typename Default,
             template<typename... > typename Operation,
             typename... Arguments>
    struct detector<Default,
                    void_t<Operation<Arguments...>>,
                    Operation,
                    Arguments... > {
        using value_type = std::true_type;
        using type = Operation<Arguments...>;
    };

} // namespace details

template <template <typename... > typename Operation,
          typename... Arguments>
using is_detected =
        typename details::detector <nonesuch,
                                    void,
                                    Operation,
                                    Arguments...>::value_type;

template <template <typename... > typename Operation,
          typename... Arguments>
using is_detected_t = is_detected<Operation, Arguments...>;

template <template <typename... > typename Operation,
          typename... Arguments>
constexpr auto const is_detected_v{ is_detected<Operation, Arguments...>{} };

template <template <typename... > typename Operation,
          typename... Arguments>
using detected_t =
    typename details::detector <nonesuch,
                                void,
                                Operation,
                                Arguments...>::type;
template <template <typename... > typename Operation,
          typename... Arguments>
constexpr auto const detected_v{ detected_t<Operation, Arguments...>{} };

template <typename Default,
          template <typename... > typename Operation,
          typename... Arguments>
using detected_or =
    details::detector <Default,
                       void,
                       Operation,
                       Arguments...>;
template <typename Default,
          template <typename... > typename Operation,
          typename... Arguments>
using detected_or_t = typename detected_or<Default, Operation, Arguments...>::type;
template <typename Default,
          template <typename... > typename Operation,
          typename... Arguments>
constexpr auto const detected_or_v{ typename detected_or<Default, Operation, Arguments...>::type{} };
template <typename ExpectedType,
          template <typename... > typename Operation,
          typename... Arguments>
using is_detected_exact =
    std::is_same<ExpectedType,
                 detected_t<Operation,
                            Arguments... >>;
template <typename ExpectedType,
          template <typename... > typename Operation,
          typename... Arguments>
constexpr auto const is_detected_exact_v{ is_detected_exact<ExpectedType, Operation, Arguments...>{} };
template <typename ConvertibleToType,
          template <typename... > typename Operation,
          typename... Arguments>
using is_detected_convertible =
            std::is_convertible<detected_t<Operation,
                                           Arguments... >,
                                ConvertibleToType>;
template <typename ConvertibleToType,
          template <typename... > typename Operation,
          typename... Arguments>
constexpr auto const is_detected_convertible_v{ is_detected_convertible<ConvertibleToType, Operation, Arguments...>{} };

} //namespace iffl::mpl;