qswiki/database/hdr/sqlite_modern_cpp/utility/function_traits.h

#pragma once

#include <tuple>
#include<type_traits>

namespace sqlite {
	namespace utility {

		template<typename> struct function_traits;

		template <typename Function>
		struct function_traits : public function_traits<
			decltype(&std::remove_reference<Function>::type::operator())
		> { };

		template <
			typename    ClassType,
			typename    ReturnType,
			typename... Arguments
		>
		struct function_traits<
			ReturnType(ClassType::*)(Arguments...) const
		> : function_traits<ReturnType(*)(Arguments...)> { };

    /* support the non-const operator ()
     * this will work with user defined functors */
		template <
			typename    ClassType,
			typename    ReturnType,
			typename... Arguments
		>
		struct function_traits<
			ReturnType(ClassType::*)(Arguments...)
		> : function_traits<ReturnType(*)(Arguments...)> { };

		template <
			typename    ReturnType,
			typename... Arguments
		>
		struct function_traits<
			ReturnType(*)(Arguments...)
		> {
			typedef ReturnType result_type;

			template <std::size_t Index>
			using argument = typename std::tuple_element<
				Index,
				std::tuple<Arguments...>
			>::type;

			static const std::size_t arity = sizeof...(Arguments);
		};

	}
}