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1.test_callable_plain，作用：判断参数是否与函数声明一致

using false_t = char;
struct true_t {
	false_t data[2];
};
static_assert(sizeof(false_t) != sizeof(true_t), "I can't work :(");

template <
	typename Method,
	typename ...Args,
	typename = decltype(std::declval<Method>()(
		std::declval<Args>()...))>
true_t test_callable_plain(Method &&, Args &&...) noexcept;
false_t test_callable_plain(...) noexcept;

template <typename Method, typename ...Args>
struct is_callable_plain
	: std::bool_constant<(
		sizeof(test_callable_plain(
			std::declval<Method>(),
			std::declval<Args>()...
		)) == sizeof(true_t))> {
};

template <typename Method, typename ...Args>
constexpr bool is_callable_plain_v = is_callable_plain<Method, Args...>::value;



//使用示例代码
void FnC(int age, string name) {
    
}

int main()
{
    auto c1 = test_callable_plain(FnC, 1);        //c1值为false_t
    auto c2 = test_callable_plain(FnC, 1,"FFF");    //c2值为true_t
    constexpr auto c3 = is_callable_plain_v<decltype(FnC), int>; //false
    constexpr auto c4 = is_callable_plain_v<decltype(FnC), int,string>;//true
}