std::is_abstract - cppreference.com (original) (raw)

| | | | | ----------------------------------------- | | ------------- | | template< class T > struct is_abstract; | | (since C++11) |

std::is_abstract is a UnaryTypeTrait.

If T is an abstract class (that is, a non-union class that declares or inherits at least one pure 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_abstract or std::is_abstract_v, the behavior is undefined.

Contents

• 1 Template parameters
• 2 Helper variable template
• 3 Inherited from std::integral_constant
  • 3.1 Member constants
  • 3.2 Member functions
  • 3.3 Member types
  • 3.4 Example
  • 3.5 Defect reports
  • 3.6 See also

[edit] Template parameters

[edit] Helper variable template

| template< class T > constexpr bool is_abstract_v = is_abstract<T>::value; | | (since C++17) | | ------------------------------------------------------------------------------- | | ------------- |

Inherited from std::integral_constant

Member constants

| | true if T is an abstract class type, false otherwise (public static member constant) | | ---------------------------------------------------------------------------------------------------------------------------------------------------------- |

Member functions

| | converts the object to bool, returns value (public member function) | | ---------------------------------------------------------------------- | | | returns value (public member function) |

Member types

[edit] Example

#include #include   struct A { int m; }; static_assert(std::is_abstract_v == false);   struct B { virtual void foo(); }; static_assert(std::is_abstract_v == false);   struct C { virtual void foo() = 0; }; static_assert(std::is_abstract_v == true);   struct D : C {}; static_assert(std::is_abstract_v == true);   struct E : C { void foo() override {} }; static_assert(std::is_abstract_v == false);   int main() {}

[edit] Defect reports

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

[edit] See also

| | checks if a type is a non-union class type (class template) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | | checks if a type is a polymorphic class type (class template) [edit] |