std::negation

 

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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)>.

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

Example

Run this code

#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,
    "");
 
static_assert(std::negation_v<std::bool_constant<true>> == false);
static_assert(std::negation_v<std::bool_constant<false>> == true);
 
int main() {}

See also

conjunction (C++17)	variadic logical AND metafunction (class template)
disjunction (C++17)	variadic logical OR metafunction (class template)
integral_constantbool_constant (C++11)(C++17)	compile-time constant of specified type with specified value (class template)