traits.hpp

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#pragma once
 
#include <concepts> // IWYU pragma: keep
#include <cstddef>
#include <tuple>
#include <type_traits>
 
#include "../../slots/direct_out.hpp"
 
namespace yorch::detail {
 
template <typename T, typename = void>
struct function_traits;
 
template <typename R, typename... Args>
struct function_traits<R(Args...)> {
    using result_type = R;
 
    static constexpr std::size_t arity = sizeof...(Args);
 
    template <std::size_t I>
    using arg = std::tuple_element_t<I, std::tuple<Args...>>;
};
 
template <typename R, typename... Args>
struct function_traits<R (*)(Args...)> : function_traits<R(Args...)> {};
 
template <typename R, typename... Args>
struct function_traits<R (*)(Args...) noexcept> : function_traits<R(Args...)> {};
 
template <typename R, typename... Args>
struct function_traits<R (&)(Args...)> : function_traits<R(Args...)> {};
 
template <typename R, typename... Args>
struct function_traits<R (&)(Args...) noexcept> : function_traits<R(Args...)> {};
 
template <typename C, typename R, typename... Args>
struct function_traits<R (C::*)(Args...)> : function_traits<R(Args...)> {};
 
template <typename C, typename R, typename... Args>
struct function_traits<R (C::*)(Args...) noexcept> : function_traits<R(Args...)> {};
 
template <typename C, typename R, typename... Args>
struct function_traits<R (C::*)(Args...) const> : function_traits<R(Args...)> {};
 
template <typename C, typename R, typename... Args>
struct function_traits<R (C::*)(Args...) const noexcept> : function_traits<R(Args...)> {};
 
template <typename F>
struct function_traits<
    F,
    std::void_t<decltype(&std::remove_reference_t<F>::operator())>>
    : function_traits<decltype(&std::remove_reference_t<F>::operator())> {};
 
template <typename T>
struct is_member_function_pointer_callable
    : std::bool_constant<std::is_member_function_pointer_v<std::remove_cvref_t<T>>> {};
 
template <typename T>
inline constexpr bool is_member_function_pointer_callable_v =
    is_member_function_pointer_callable<T>::value;
 
template <typename T, typename = void>
struct member_function_traits;
 
template <typename C, typename R, typename... Args>
struct member_function_traits<R (C::*)(Args...)> {
    using class_type = C;
    using receiver_arg_type = C&;
    using result_type = R;
 
    static constexpr std::size_t arity = sizeof...(Args);
 
    template <std::size_t I>
    using arg = std::tuple_element_t<I, std::tuple<Args...>>;
};
 
template <typename C, typename R, typename... Args>
struct member_function_traits<R (C::*)(Args...) noexcept>
    : member_function_traits<R (C::*)(Args...)> {};
 
template <typename C, typename R, typename... Args>
struct member_function_traits<R (C::*)(Args...) const> {
    using class_type = C;
    using receiver_arg_type = const C&;
    using result_type = R;
 
    static constexpr std::size_t arity = sizeof...(Args);
 
    template <std::size_t I>
    using arg = std::tuple_element_t<I, std::tuple<Args...>>;
};
 
template <typename C, typename R, typename... Args>
struct member_function_traits<R (C::*)(Args...) const noexcept>
    : member_function_traits<R (C::*)(Args...) const> {};
 
template <std::size_t I, typename F>
using nth_arg_t = typename function_traits<std::remove_cvref_t<F>>::template arg<I>;
 
template <typename F>
using result_t = typename function_traits<std::remove_cvref_t<F>>::result_type;
 
template <typename F>
using member_result_t =
    typename member_function_traits<std::remove_cvref_t<F>>::result_type;
 
template <typename F>
using member_class_t =
    typename member_function_traits<std::remove_cvref_t<F>>::class_type;
 
template <typename F>
using member_receiver_arg_t =
    typename member_function_traits<std::remove_cvref_t<F>>::receiver_arg_type;
 
template <typename F>
using member_borrowed_receiver_t =
    std::remove_reference_t<member_receiver_arg_t<F>>;
 
template <std::size_t I, typename F>
using member_nth_arg_t =
    typename member_function_traits<std::remove_cvref_t<F>>::template arg<I>;
 
template <typename F>
inline constexpr std::size_t last_arg_index_v =
    function_traits<std::remove_cvref_t<F>>::arity - 1;
 
template <typename F>
using last_arg_t =
    nth_arg_t<last_arg_index_v<F>, F>;
 
template <typename F>
inline constexpr std::size_t member_last_arg_index_v =
    member_function_traits<std::remove_cvref_t<F>>::arity - 1;
 
template <typename F>
using member_last_arg_t =
    member_nth_arg_t<member_last_arg_index_v<F>, F>;
 
template <typename T>
struct direct_out_arg : std::false_type {};
 
template <typename T>
struct direct_out_arg<direct_out<T>> : std::true_type {};
 
template <typename T>
inline constexpr bool direct_out_arg_v =
    direct_out_arg<std::remove_cvref_t<T>>::value;
 
template <typename T>
concept direct_out_arg_like =
    direct_out_arg_v<T>;
 
template <typename T, typename = void>
struct direct_out_payload;
 
template <typename T>
struct direct_out_payload<direct_out<T>, void> {
    using type = T;
};
 
template <typename T>
using direct_out_payload_t = typename direct_out_payload<T>::type;
 
template <typename F>
concept bind_callable =
    requires {
        { function_traits<std::remove_cvref_t<F>>::arity } -> std::convertible_to<std::size_t>;
    };
 
template <typename F>
concept member_bind_callable =
    is_member_function_pointer_callable_v<F> &&
    requires {
        typename member_function_traits<std::remove_cvref_t<F>>::class_type;
    };
 
template <typename F>
concept inferable_direct_output_callable =
    bind_callable<F> &&
    !member_bind_callable<F> &&
    function_traits<std::remove_cvref_t<F>>::arity > 0 &&
    direct_out_arg_like<last_arg_t<std::remove_cvref_t<F>>>;
 
template <typename F>
concept ordinary_bind_callable =
    bind_callable<F> &&
    !member_bind_callable<F> &&
    !inferable_direct_output_callable<F>;
 
template <typename F>
concept inferable_forward_prev_callable =
    ordinary_bind_callable<F>;
 
template <typename F>
concept inferable_direct_output_member_callable =
    member_bind_callable<F> &&
    member_function_traits<std::remove_cvref_t<F>>::arity > 0 &&
    direct_out_arg_like<member_last_arg_t<std::remove_cvref_t<F>>>;
 
template <typename F>
concept ordinary_member_bind_callable =
    member_bind_callable<F> &&
    !inferable_direct_output_member_callable<F>;
 
template <typename F, typename... Specs>
concept bind_signature_matches =
    ordinary_bind_callable<F> &&
    function_traits<std::remove_cvref_t<F>>::arity == sizeof...(Specs);
 
template <typename F, typename ReceiverSpec>
concept member_receiver_bindable =
    member_bind_callable<F>;
 
template <typename F, typename... Specs>
concept member_bound_signature_matches =
    ordinary_member_bind_callable<F> &&
    member_function_traits<std::remove_cvref_t<F>>::arity == sizeof...(Specs);
 
template <typename T, typename F, typename... Specs>
concept bind_into_signature_matches =
    inferable_direct_output_callable<F> &&
    function_traits<std::remove_cvref_t<F>>::arity == sizeof...(Specs) + 1 &&
    std::is_same_v<
        std::remove_cvref_t<last_arg_t<std::remove_cvref_t<F>>>,
        direct_out<T>>;
 
template <typename T, typename F, typename... Specs>
concept member_bound_into_signature_matches =
    inferable_direct_output_member_callable<F> &&
    member_function_traits<std::remove_cvref_t<F>>::arity == sizeof...(Specs) + 1 &&
    std::is_same_v<
        std::remove_cvref_t<member_last_arg_t<std::remove_cvref_t<F>>>,
        direct_out<T>>;
 
template <typename F, typename... Specs>
concept inferred_bind_into_signature_matches =
    inferable_direct_output_callable<F> &&
    function_traits<std::remove_cvref_t<F>>::arity == sizeof...(Specs) + 1;
 
template <typename F, typename... Specs>
concept inferred_forward_prev_signature_matches =
    inferable_forward_prev_callable<F> &&
    function_traits<std::remove_cvref_t<F>>::arity == sizeof...(Specs);
 
template <typename F, typename... Specs>
concept inferred_member_bound_into_signature_matches =
    inferable_direct_output_member_callable<F> &&
    member_function_traits<std::remove_cvref_t<F>>::arity == sizeof...(Specs) + 1;
 
} // namespace yorch::detail