W3cubDocs

/C++

std::negation

Defined in header `<type_traits>`
template<class B> struct negation;	(1)	(since C++17)

Forms the logical negation of the type trait B.

The type std::negation<B> is a UnaryTypeTrait with a BaseCharacteristic of std::bool_constant<!bool(B::value)>.

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)> { };

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

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)