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std::is_polymorphic(3) C++ Standard Libary std::is_polymorphic(3) NAME std::is_polymorphic - std::is_polymorphic Synopsis Defined in header <type_traits> template< class T > (since C++11) struct is_polymorphic; std::is_polymorphic is a UnaryTypeTrait. If T is a polymorphic class (that is, a non-union class that de- clares 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 unde- fined. 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 > (since C++17) inline constexpr bool is_polymorphic_v = is_polymorphic<T>::value; Inherited from std::integral_constant Member constants value true if T is a polymorphic class type, false otherwise [static] (public static member constant) Member functions operator bool converts the object to bool, returns value (public member function) operator() returns value (C++14) (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*>(sta- tic_cast<T*>(nullptr))) ); template<class T> std::false_type detect_is_polymorphic(...); } // namespace detail template<class T> struct is_polymorphic : decltype(detail::detect_is_polymor- phic<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 retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct be- havior LWG 2015 C++11 the behavior was undefined if the base charac- teristic is T is an incomplete union type std::false_type in this case See also is_class checks if a type is a non-union class type (C++11) (class template) is_abstract checks if a type is an abstract class type (C++11) (class template) has_virtual_destructor checks if a type has a virtual destructor (C++11) (class template) http://cppreference.com 2024.06.10 std::is_polymorphic(3)
NAME | Synopsis | Template parameters | Member constants | Member functions | Member types | Possible implementation | Example | See also
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