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    std::is_union

    From cppreference.com
     
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    Defined in header <type_traits>
    template< class T > struct is_union;
    		 (since C++11)
    See More

    std::is_union is a UnaryTypeTrait.

    Checks whether T is a union type. Provides the member constant value, which is equal to true if T is a union type. Otherwise, value is equal to false.

    If the program adds specializations for std::is_union or std::is_union_v, the behavior is undefined.

    Template parameters

    T - a type to check

    Helper variable template

    template< class T > constexpr bool is_union_v = is_union<T>::value;
    		 (since C++17)
    [edit]

    Inherited from std::integral_constant

    Member constants

    value
    [static]
    		 true if T is a union type, 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>

    Example

    Run this code
    #include <type_traits>

struct A {};
static_assert(!std::is_union_v<A>);

typedef union
{
    int a;
    float b;
} B;
static_assert(std::is_union_v<B>);

struct C { B d; };
static_assert(!std::is_union_v<C>);

static_assert(!std::is_union_v<int>);

int main() {}

    See also

    (C++11)
    		 checks if a type is a non-union class type
    (class template) [edit]