is_invocable_impl.hpp

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#ifndef BOOST_CLBL_TRTS_IS_INVOCABLE_IMPL_HPP
#define BOOST_CLBL_TRTS_IS_INVOCABLE_IMPL_HPP
 
#include <boost/callable_traits/detail/config.hpp>
#include <boost/callable_traits/detail/forward_declarations.hpp>
#include <boost/callable_traits/detail/utility.hpp>
#include <type_traits>
#include <utility>
 
namespace boost { namespace callable_traits { namespace detail {
 
    template<typename T>
    struct can_dereference_t
    {
        template<typename>
        struct check {};
 
        template<typename U>
        static std::int8_t test(
            check<typename std::remove_reference<decltype(*std::declval<U>())>::type>*
        );
 
        template<typename>
        static std::int16_t test(...);
 
        static constexpr const bool value =
            sizeof(test<T>(nullptr)) == sizeof(std::int8_t);
    };
 
    //returns std::true_type for pointers and smart pointers
    template<typename T>
    using can_dereference = std::integral_constant<bool,
        can_dereference_t<T>::value>;
 
 
    template<typename T, typename = std::true_type>
    struct generalize_t {
        using type = T;
    };
 
    template<typename T>
    struct generalize_t<T, std::integral_constant<bool,
            can_dereference<T>::value && !is_reference_wrapper<T>::value
    >>{
        using type = decltype(*std::declval<T>());
    };
 
    template<typename T>
    struct generalize_t<T, is_reference_wrapper<T>> {
        using type = decltype(std::declval<T>().get());
    };
 
    // When T is a pointer, generalize<T> is the resulting type of the
    // pointer dereferenced. When T is an std::reference_wrapper, generalize<T>
    // is the underlying reference type. Otherwise, generalize<T> is T.
    template<typename T>
    using generalize = typename generalize_t<T>::type;
 
    // handles the member pointer rules of INVOKE
    template<typename Base, typename T,
             typename IsBaseOf = std::is_base_of<Base, shallow_decay<T>>,
             typename IsSame = std::is_same<Base, shallow_decay<T>>>
    using generalize_if_dissimilar = typename std::conditional<
        IsBaseOf::value || IsSame::value, T, generalize<T>>::type;
 
    template<typename Traits, bool = Traits::is_const_member::value
        || Traits::is_volatile_member::value
        || Traits::is_lvalue_reference_member::value
        || Traits::is_rvalue_reference_member::value>
    struct test_invoke {
 
        template<typename... Rgs,
            typename U = typename Traits::type>
        auto operator()(int, Rgs&&... rgs) const ->
            success<decltype(std::declval<U>()(static_cast<Rgs&&>(rgs)...))>;
 
        auto operator()(long, ...) const -> substitution_failure;
    };
 
    template<typename F>
    struct test_invoke<function<F>, true /*abominable*/> {
        auto operator()(...) const -> substitution_failure;
    };
 
    template<typename Pmf, bool Ignored>
    struct test_invoke<pmf<Pmf>, Ignored> {
 
        using class_t = typename pmf<Pmf>::class_type;
 
       template<typename U, typename... Rgs,
            typename Obj = generalize_if_dissimilar<class_t, U&&>>
        auto operator()(int, U&& u, Rgs&&... rgs) const ->
            success<decltype((std::declval<Obj>().*std::declval<Pmf>())(static_cast<Rgs&&>(rgs)...))>;
 
        auto operator()(long, ...) const -> substitution_failure;
    };
 
    template<typename Pmd, bool Ignored>
    struct test_invoke<pmd<Pmd>, Ignored> {
 
        using class_t = typename pmd<Pmd>::class_type;
 
        template<typename U,
            typename Obj = generalize_if_dissimilar<class_t, U&&>>
        auto operator()(int, U&& u) const ->
            success<decltype(std::declval<Obj>().*std::declval<Pmd>())>;
 
        auto operator()(long, ...) const -> substitution_failure;
    };
 
    template<typename T, typename... Args>
    struct is_invocable_impl {
        using traits = detail::traits<T>;
        using test = detail::test_invoke<traits>;
        using result = decltype(test{}(0, ::std::declval<Args>()...));
        using type = std::integral_constant<bool, result::value>;
    };
 
    template<typename... Args>
    struct is_invocable_impl<void, Args...> {
        using type = std::false_type;
    };
 
    template<typename IsInvocable, typename Ret, typename T, typename... Args>
    struct is_invocable_r_impl {
        using traits = detail::traits<T>;
        using test = detail::test_invoke<traits>;
        using result = decltype(test{}(0, ::std::declval<Args>()...));
        using type = std::integral_constant<bool,
            std::is_convertible<typename result::_::type, Ret>::value
                || std::is_same<Ret, void>::value>;
    };
 
    template<typename Ret, typename T, typename... Args>
    struct is_invocable_r_impl<std::false_type, Ret, T, Args...> {
        using type = std::false_type;
    };
 
}}} // namespace boost::callable_traits::detail
 
#endif // #ifndef BOOST_CLBL_TRTS_IS_INVOCABLE_IMPL_HPP