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std::negation

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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)>.

Contents

[edit] Template parameters

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

[edit] 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>

[edit] Possible implementation

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

[edit] 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

[edit] See also

variadic logical AND metafunction
(class template) [edit]
variadic logical OR metafunction
(class template) [edit]
compile-time constant of specified type with specified value
(class template) [edit]