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    std::negation

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

    Forms the logical negation of the type trait B.

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

    If the program adds specializations for std::negation or std::negation_v, the behavior is undefined.

    Template parameters

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

    Helper variable template

    template< class B > constexpr bool negation_v = negation<B>::value;
    		 (since C++17)
    [edit]

    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)> { };

    Notes

    Feature-test macro Value Std Feature
    __cpp_lib_logical_traits 201510L (C++17) Logical operator type traits

    Example

    Run this code
    #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,
    "");

static_assert(std::negation_v<std::bool_constant<true>> == false);
static_assert(std::negation_v<std::bool_constant<false>> == true);

int main() {}

    See also

    (C++17)
    		 variadic logical AND metafunction
    (class template) [edit]
    (C++17)
    		 variadic logical OR metafunction
    (class template) [edit]
    (C++11)(C++17)
    		 compile-time constant of specified type with specified value
    (class template) [edit]