delegate.hpp

#ifndef ENTT_SIGNAL_DELEGATE_HPP
#define ENTT_SIGNAL_DELEGATE_HPP
 
 
#include <tuple>
#include <cstddef>
#include <utility>
#include <functional>
#include <type_traits>
#include "../config/config.h"
 
 
namespace entt {
 
 
namespace internal {
 
 
template<typename Ret, typename... Args>
auto function_pointer(Ret(*)(Args...)) -> Ret(*)(Args...);
 
 
template<typename Ret, typename Type, typename... Args, typename Other>
auto function_pointer(Ret(*)(Type, Args...), Other &&) -> Ret(*)(Args...);
 
 
template<typename Class, typename Ret, typename... Args, typename... Other>
auto function_pointer(Ret(Class:: *)(Args...), Other &&...) -> Ret(*)(Args...);
 
 
template<typename Class, typename Ret, typename... Args, typename... Other>
auto function_pointer(Ret(Class:: *)(Args...) const, Other &&...) -> Ret(*)(Args...);
 
 
template<typename Class, typename Type, typename... Other>
auto function_pointer(Type Class:: *, Other &&...) -> Type(*)();
 
 
template<typename... Type>
using function_pointer_t = decltype(internal::function_pointer(std::declval<Type>()...));
 
 
template<typename... Class, typename Ret, typename... Args>
constexpr auto index_sequence_for(Ret(*)(Args...)) {
    return std::index_sequence_for<Class..., Args...>{};
}
 
 
}
 
 
template<auto>
struct connect_arg_t {};
 
 
template<auto Func>
constexpr connect_arg_t<Func> connect_arg{};
 
 
template<typename>
class delegate;
 
 
template<typename Ret, typename... Args>
class delegate<Ret(Args...)> {
    using proto_fn_type = Ret(const void *, Args...);
 
    template<auto Candidate, std::size_t... Index>
    auto wrap(std::index_sequence<Index...>) ENTT_NOEXCEPT {
        return [](const void *, Args... args) -> Ret {
            const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            return Ret(std::invoke(Candidate, std::forward<std::tuple_element_t<Index, std::tuple<Args...>>>(std::get<Index>(arguments))...));
        };
    }
 
    template<auto Candidate, typename Type, std::size_t... Index>
    auto wrap(Type &, std::index_sequence<Index...>) ENTT_NOEXCEPT {
        return [](const void *payload, Args... args) -> Ret {
            const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<std::conditional_t<std::is_const_v<Type>, const void *, void *>>(payload));
            return Ret(std::invoke(Candidate, *curr, std::forward<std::tuple_element_t<Index, std::tuple<Args...>>>(std::get<Index>(arguments))...));
        };
    }
 
    template<auto Candidate, typename Type, std::size_t... Index>
    auto wrap(Type *, std::index_sequence<Index...>) ENTT_NOEXCEPT {
        return [](const void *payload, Args... args) -> Ret {
            const auto arguments = std::forward_as_tuple(std::forward<Args>(args)...);
            Type *curr = static_cast<Type *>(const_cast<std::conditional_t<std::is_const_v<Type>, const void *, void *>>(payload));
            return Ret(std::invoke(Candidate, curr, std::forward<std::tuple_element_t<Index, std::tuple<Args...>>>(std::get<Index>(arguments))...));
        };
    }
 
public:
    using function_type = Ret(Args...);
 
    delegate() ENTT_NOEXCEPT
        : fn{nullptr}, data{nullptr}
    {}
 
    template<auto Candidate>
    delegate(connect_arg_t<Candidate>) ENTT_NOEXCEPT
        : delegate{}
    {
        connect<Candidate>();
    }
 
    template<auto Candidate, typename Type>
    delegate(connect_arg_t<Candidate>, Type &&value_or_instance) ENTT_NOEXCEPT
        : delegate{}
    {
        connect<Candidate>(std::forward<Type>(value_or_instance));
    }
 
    template<auto Candidate>
    void connect() ENTT_NOEXCEPT {
        data = nullptr;
 
        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Args...>) {
            fn = [](const void *, Args... args) -> Ret {
                return Ret(std::invoke(Candidate, std::forward<Args>(args)...));
            };
        } else if constexpr(std::is_member_pointer_v<decltype(Candidate)>) {
            fn = wrap<Candidate>(internal::index_sequence_for<std::tuple_element_t<0, std::tuple<Args...>>>(internal::function_pointer_t<decltype(Candidate)>{}));
        } else {
            fn = wrap<Candidate>(internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate)>{}));
        }
    }
 
    template<auto Candidate, typename Type>
    void connect(Type &value_or_instance) ENTT_NOEXCEPT {
        data = &value_or_instance;
 
        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type &, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<std::conditional_t<std::is_const_v<Type>, const void *, void *>>(payload));
                return Ret(std::invoke(Candidate, *curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }
 
    template<auto Candidate, typename Type>
    void connect(Type *value_or_instance) ENTT_NOEXCEPT {
        data = value_or_instance;
 
        if constexpr(std::is_invocable_r_v<Ret, decltype(Candidate), Type *, Args...>) {
            fn = [](const void *payload, Args... args) -> Ret {
                Type *curr = static_cast<Type *>(const_cast<std::conditional_t<std::is_const_v<Type>, const void *, void *>>(payload));
                return Ret(std::invoke(Candidate, curr, std::forward<Args>(args)...));
            };
        } else {
            fn = wrap<Candidate>(value_or_instance, internal::index_sequence_for(internal::function_pointer_t<decltype(Candidate), Type>{}));
        }
    }
 
    void reset() ENTT_NOEXCEPT {
        fn = nullptr;
        data = nullptr;
    }
 
    const void * instance() const ENTT_NOEXCEPT {
        return data;
    }
 
    Ret operator()(Args... args) const {
        ENTT_ASSERT(fn);
        return fn(data, std::forward<Args>(args)...);
    }
 
    explicit operator bool() const ENTT_NOEXCEPT {
        // no need to test also data
        return !(fn == nullptr);
    }
 
    bool operator==(const delegate<Ret(Args...)> &other) const ENTT_NOEXCEPT {
        return fn == other.fn && data == other.data;
    }
 
private:
    proto_fn_type *fn;
    const void *data;
};
 
 
template<typename Ret, typename... Args>
bool operator!=(const delegate<Ret(Args...)> &lhs, const delegate<Ret(Args...)> &rhs) ENTT_NOEXCEPT {
    return !(lhs == rhs);
}
 
 
template<auto Candidate>
delegate(connect_arg_t<Candidate>) ENTT_NOEXCEPT
-> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate)>>>;
 
 
template<auto Candidate, typename Type>
delegate(connect_arg_t<Candidate>, Type &&) ENTT_NOEXCEPT
-> delegate<std::remove_pointer_t<internal::function_pointer_t<decltype(Candidate), Type>>>;
 
 
}
 
 
#endif