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    std::is_polymorphic

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

    std::is_polymorphic is a UnaryTypeTrait.

    If T is a polymorphic class (that is, a non-union class that declares or inherits at least one virtual function), provides the member constant value equal to true. For any other type, value is false.

    If T is an incomplete non-union class type, the behavior is undefined.

    If the program adds specializations for std::is_polymorphic or std::is_polymorphic_v, the behavior is undefined.

    Template parameters

    T - a type to check

    Helper variable template

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

    Inherited from std::integral_constant

    Member constants

    value
    [static]
    		 true if T is a polymorphic class 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>

    Possible implementation

    namespace detail
{
    template<class T>
    std::true_type detect_is_polymorphic(
        decltype(dynamic_cast<const volatile void*>(static_cast<T*>(nullptr)))
    );
    template<class T>
    std::false_type detect_is_polymorphic(...);
} // namespace detail

template<class T>
struct is_polymorphic : decltype(detail::detect_is_polymorphic<T>(nullptr)) {};

    Example

    Run this code
    #include <type_traits>
 
struct A { int m; };
static_assert(!std::is_polymorphic_v<A>);

struct B { virtual void foo(); };
static_assert(std::is_polymorphic_v<B>);

struct C : B {};
static_assert(std::is_polymorphic_v<C>);
 
struct D { virtual ~D() = default; };
static_assert(std::is_polymorphic_v<D>);
 
// Uses inheritance, but not the virtual keyword:
struct E : A {};
static_assert(!std::is_polymorphic_v<E>);

struct F : virtual A {};
static_assert(!std::is_polymorphic_v<F>);

struct AX : A {};
struct AY : A {};
struct XY : virtual AX, virtual AY {};
static_assert(!std::is_polymorphic_v<XY>);
 
int main() {}

    Defect reports

    The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

    DR Applied to Behavior as published Correct behavior
    LWG 2015 C++11 the behavior was undefined if
    T is an incomplete union type     		the base characteristic is
    std::false_type in this case

    See also

    (C++11)
    		 checks if a type is a non-union class type
    (class template) [edit]
    (C++11)
    		 checks if a type is an abstract class type
    (class template) [edit]
    (C++11)
    		 checks if a type has a virtual destructor
    (class template) [edit]