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102 lines
2.9 KiB
C++
102 lines
2.9 KiB
C++
#ifndef ENTT_CORE_UTILITY_HPP
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#define ENTT_CORE_UTILITY_HPP
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#include <type_traits>
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#include <utility>
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namespace entt {
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/*! @brief Identity function object (waiting for C++20). */
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struct identity {
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/*! @brief Indicates that this is a transparent function object. */
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using is_transparent = void;
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/**
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* @brief Returns its argument unchanged.
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* @tparam Type Type of the argument.
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* @param value The actual argument.
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* @return The submitted value as-is.
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*/
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template<class Type>
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[[nodiscard]] constexpr Type &&operator()(Type &&value) const noexcept {
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return std::forward<Type>(value);
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}
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};
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/**
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* @brief Constant utility to disambiguate overloaded members of a class.
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* @tparam Type Type of the desired overload.
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* @tparam Class Type of class to which the member belongs.
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* @param member A valid pointer to a member.
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* @return Pointer to the member.
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*/
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template<typename Type, typename Class>
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[[nodiscard]] constexpr auto overload(Type Class::*member) noexcept {
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return member;
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}
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/**
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* @brief Constant utility to disambiguate overloaded functions.
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* @tparam Func Function type of the desired overload.
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* @param func A valid pointer to a function.
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* @return Pointer to the function.
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*/
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template<typename Func>
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[[nodiscard]] constexpr auto overload(Func *func) noexcept {
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return func;
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}
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/**
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* @brief Helper type for visitors.
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* @tparam Func Types of function objects.
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*/
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template<class... Func>
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struct overloaded: Func... {
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using Func::operator()...;
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};
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/**
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* @brief Deduction guide.
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* @tparam Func Types of function objects.
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*/
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template<class... Func>
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overloaded(Func...) -> overloaded<Func...>;
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/**
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* @brief Basic implementation of a y-combinator.
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* @tparam Func Type of a potentially recursive function.
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*/
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template<class Func>
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struct y_combinator {
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/**
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* @brief Constructs a y-combinator from a given function.
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* @param recursive A potentially recursive function.
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*/
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constexpr y_combinator(Func recursive) noexcept(std::is_nothrow_move_constructible_v<Func>)
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: func{std::move(recursive)} {}
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/**
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* @brief Invokes a y-combinator and therefore its underlying function.
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* @tparam Args Types of arguments to use to invoke the underlying function.
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* @param args Parameters to use to invoke the underlying function.
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* @return Return value of the underlying function, if any.
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*/
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template<class... Args>
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constexpr decltype(auto) operator()(Args &&...args) const noexcept(std::is_nothrow_invocable_v<Func, const y_combinator &, Args...>) {
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return func(*this, std::forward<Args>(args)...);
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}
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/*! @copydoc operator()() */
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template<class... Args>
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constexpr decltype(auto) operator()(Args &&...args) noexcept(std::is_nothrow_invocable_v<Func, y_combinator &, Args...>) {
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return func(*this, std::forward<Args>(args)...);
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}
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private:
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Func func;
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};
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} // namespace entt
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#endif
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