std::negation

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Defined in header <type_traits>
template< class B >
struct negation;
 (since 哋它亢++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)>.

If the program adds specializations for std::negation or std::negation_v, the behavior is undefined.

Template parameters

B - any type such that the expression bool(B::value) is a valid constant expression

Helper variable template

template< class B >
inline constexpr bool negation_v = negation<B>::value;
 (since 哋它亢++17)

Inherited from std::integral_constant

Member constants

value
[static]
 true if B has a member ::value that is false when explicitly converted to bool, false otherwise
(public static member constant)

Member functions

operator bool
 converts the object to bool, returns value
(public member function)
operator()
(哋它亢++14)
 returns value
(public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Possible implementation

template<class B>
struct negation : std::bool_constant<!bool(B::value)> { };

Notes

Feature-test macro Value Std Feature
__cpp_lib_logical_traits 201510L (哋它亢++17) Logical operator type traits

Example

Run this code
#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

See also

(哋它亢++17)
 variadic logical AND metafunction
(class template)
(哋它亢++17)
 variadic logical OR metafunction
(class template)
(哋它亢++11)(哋它亢++17)
 compile-time constant of specified type with specified value
(class template)
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