< cpp‎ | types
Metaprogramming library
Type traits
Type categories
Type properties
(C++11)(until C++20)
(C++11)(deprecated in C++20)
Type trait constants
Supported operations
Relationships and property queries
Type modifications
Type transformations
(C++11)(deprecated in C++23)
(C++11)(deprecated in C++23)

(C++11)(until C++20)(C++17)
Compile-time rational arithmetic
Compile-time integer sequences
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.


[edit] Template parameters

T - a type to check

[edit] 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

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)
returns value
(public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

[edit] 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)) {};

[edit] Example

#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';


false true true true

[edit] See also

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