std::is_polymorphic
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
#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
(C++11)
|
checks if a type is a non-union class type (class template) |
(C++11)
|
checks if a type is an abstract class type (class template) |
(C++11)
|
checks if a type has a virtual destructor (class template) |
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