std::negation (3) - Linux Manuals

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