Difference between revisions of "cpp/types/negation"
From cppreference.com
m (Text replace - "{{concept" to "{{named req") |
(~) |
||
| Line 12: | Line 12: | ||
The type {{c|std::negation<B>}} is a {{named req|UnaryTypeTrait}} with a BaseCharacteristic of {{c|std::bool_constant<!bool(B::value)>}}. | The type {{c|std::negation<B>}} is a {{named req|UnaryTypeTrait}} with a BaseCharacteristic of {{c|std::bool_constant<!bool(B::value)>}}. | ||
| + | |||
| + | {{cpp/types/nospec}} | ||
===Template parameters=== | ===Template parameters=== | ||
Revision as of 15:29, 24 January 2020
| 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)>.
If the program adds specializations for std::negation, the behavior is undefined.
Contents |
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
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
| (C++17) |
variadic logical AND metafunction (class template) |
| (C++17) |
variadic logical OR metafunction (class template) |
| (C++11)(C++17) |
compile-time constant of specified type with specified value (class template) |
