std::is_polymorphic

 

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Defined in header <type_traits>
template< class T > struct is_polymorphic;		(since C++11)

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 a non-union class type, T shall be a complete type; otherwise, the behavior is undefined.

The behavior of a program that adds specializations for is_polymorphic or is_polymorphic_v (since C++17) is undefined.

Template parameters

T

-

a type to check

Helper variable template

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

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 <iostream>
#include <type_traits>
 
struct A {
    int m;
};
 
struct B {
    virtual void foo();
};
 
struct C : B {};
 
struct D {
    virtual ~D() = default;
};
 
int main()
{
    std::cout << std::boolalpha
              << std::is_polymorphic<A>::value << ' '
              << std::is_polymorphic<B>::value << ' '
              << std::is_polymorphic<C>::value << ' '
              << std::is_polymorphic<D>::value << '\n';
}

Output:

false true true true

See also

is_class (C++11)	checks if a type is a non-union class type (class template)
is_abstract (C++11)	checks if a type is an abstract class type (class template)
has_virtual_destructor (C++11)	checks if a type has a virtual destructor (class template)