std::negation (3) - Linux Man Pages

std::negation: std::negation

NAME

std::negation - std::negation

Synopsis


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


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> (since C++17)
inline constexpr bool negation_v = negation<B>::value;


Inherited from std::integral_constant

Member constants


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

Member functions


              converts the object to bool, returns value
operator bool (public member function)


operator() returns value
              (public member function)
(C++14)

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


// 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


conjunction variadic logical AND metafunction
                  (class template)
(C++17)


disjunction variadic logical OR metafunction
                  (class template)
(C++17)


integral_constant
bool_constant compile-time constant of specified type with specified value
                  (class template)
(C++11)
(C++17)