std::declvalcan only be used inunevaluated contextsand is not required to be defined; it is an error to evaluate an expression that contains this function. Formally, the program is ill-formed if this function isodr-used. Parameters (none) ...
1) 如果虚构的函数定义 To test() { return std::declval<From>(); } 良构,(即 std::declval<From>() 能用隐式转换转换为 To,或 From 和To 均为可有 cv 限定的 void),那么提供的成员常量 value 等于true。否则,value 等于false。对于此项检查而言,不认为返回语句中的 std::declval 是ODR 使用。
std::declval<std::decay_t<F>const&>(),std::declval<Args>()...)); (since C++20) (2) template<class...Args> autooperator()(Args&&...args)&& ->decltype(!std::declval< std::invoke_result_t<std::decay_t<F>, Args...>>()); ...
declval (C++11) 获取到其实参的引用,用于不求值语境中 (函数模板) to_underlying (C++23) 转换枚举到其底层类型 (函数模板) 整数比较函数 在标头 <utility> 定义 cmp_equalcmp_not_equalcmp_lesscmp_greatercmp_less_equalcmp_greater_equal (C++20) 比较二个整数值,而无转换所致的值更改 (函数模...
std::tuple From cppreference.com Defined in header<tuple> template<class...Types> classtuple; (since C++11) Class templatestd::tupleis a fixed-size collection of heterogeneous values. It is a generalization ofstd::pair. Ifstd::is_trivially_destructible<Ti>::valueistruefor everyTiinTypes, ...
increment: template<class, class = void> struct has_pre_increment_member : std::false_type {}; // specialization recognizes types that do support pre-increment: template<class T> struct has_pre_increment_member<T, std::void_t<decltype(++std::declval<T&>())> > : std::true_type {};...
declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) ma...
declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) ma...
Args> struct invoke_result< decltype(void(detail::INVOKE(std::declval<F>(), std::declval<Args>()...))), F, Args...> { using type = decltype(detail::INVOKE(std::declval<F>(), std::declval<Args>()...)); }; } // namespace detail template<class> struct result_of; template<...
库函数std::invoke_r可以显式执行INVOKE<R>操作。 (C++23 起) 要求 如果满足下列条件,那么类型T是可调用(Callable)的: 给定 T类型的对象f 适合的实参类型列表ArgTypes 适合的返回类型R 那么下列表达式必须合法: 表达式要求 INVOKE<R>(f,std::declval<ArgTypes>()...)该表达式在不求值语境中良构 ...