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std::is_abstract

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

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 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.

Template parameters

a type to check

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

value

[static]

true if T is an abstract 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>`

Example

#include <iostream>
#include <type_traits>
 
struct A {
    int m;
};
 
struct B {
    virtual void foo();
};
 
struct C {
    virtual void foo() = 0;
};
 
struct D : C {};
 
int main()
{
    std::cout << std::boolalpha;
    std::cout << std::is_abstract<A>::value << '\n';
    std::cout << std::is_abstract<B>::value << '\n';
    std::cout << std::is_abstract<C>::value << '\n';
    std::cout << std::is_abstract<D>::value << '\n';
}

Output:

false
false
true
true

is_class (C++11)	checks if a type is a non-union class type (class template)
is_polymorphic (C++11)	checks if a type is polymorphic class type (class template)
std::experimental::is_abstract_v (library fundamentals TS)	variable template alias of `std::is_abstract::value` (variable template)