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std::negation

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.

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 C++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()
(C++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 Comment
__cpp_lib_logical_traits 201510L (C++17) Logical operator type traits

Example

#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

(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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