Defined in header <type_traits> | ||
|---|---|---|
template< class B > struct negation; | (since C++17) |
Forms the logical negation of the type trait B.
The type std::negation<B> is a UnaryTypeTrait with a base characteristic of std::bool_constant<!bool(B::value)>.
The behavior of a program that adds specializations for negation or negation_v is undefined.
| B | - | any type such that the expression bool(B::value) is a valid constant expression |
template< class B > inline constexpr bool negation_v = negation<B>::value; | (since C++17) |
| value
[static] | true if B has a member ::value that is false when explicitly converted to bool, false otherwise (public static member constant) |
| operator bool | converts the object to bool, returns value (public member function) |
| operator()
(C++14) | returns value (public member function) |
| Type | Definition |
|---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
template<class B>
struct negation : std::bool_constant<!bool(B::value)> { }; |
| Feature-test macro | Value | Std | Comment |
|---|---|---|---|
__cpp_lib_logical_traits | 201510L | (C++17) | Logical operator type traits |
#include <iostream>
#include <type_traits>
static_assert(
std::is_same<
std::bool_constant<false>,
typename std::negation<std::bool_constant<true>>::type>::value,
"");
static_assert(
std::is_same<
std::bool_constant<true>,
typename std::negation<std::bool_constant<false>>::type>::value,
"");
int main()
{
std::cout << std::boolalpha;
std::cout << std::negation<std::bool_constant<true>>::value << '\n';
std::cout << std::negation<std::bool_constant<false>>::value << '\n';
}Output:
false true
|
(C++17) | variadic logical AND metafunction (class template) |
|
(C++17) | variadic logical OR metafunction (class template) |
|
(C++11)(C++17) | compile-time constant of specified type with specified value (class template) |
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