type_traits.hpp

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#pragma once
 
#include <functional>
#include <tuple>
#include <type_traits>
 
namespace co_ecs::detail {
 
template<std::size_t I, typename... Args>
using nth_type_t = std::tuple_element_t<I, std::tuple<Args...>>;
 
template<typename... Args>
using first_type_t = nth_type_t<0, Args...>;
 
template<typename... Args>
using second_type_t = nth_type_t<1, Args...>;
 
template<typename F>
struct function_traits : public function_traits<decltype(std::function{ std::declval<F>() })> {};
 
template<typename R, typename... Args>
struct function_traits<std::function<R(Args...)>> {
    using return_type = R;
 
    using arguments_tuple_type = std::tuple<Args...>;
 
    template<std::size_t I>
    using argument_type = nth_type_t<I, Args...>;
 
    static constexpr std::size_t arity = sizeof...(Args);
};
 
template<typename... Rest>
struct unique_types;
 
template<>
struct unique_types<> {};
 
template<typename T1>
struct unique_types<T1> {};
 
template<class T1, class T2>
struct unique_types<T1, T2> {
    static_assert(!std::is_same<T1, T2>::value, "Types must be unique within parameter pack");
};
 
template<typename T1, typename T2, typename... Rest>
struct unique_types<T1, T2, Rest...>
    : unique_types<T1, T2>
    , unique_types<T1, Rest...>
    , unique_types<T2, Rest...> {};
 
} // namespace co_ecs::detail