std:: is_final

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Defined in header <type_traits>
template < class T >
struct is_final ;
(since C++14)

std::is_final is a UnaryTypeTrait .

If T is a final class, provides the member constant value equal true . For any other type, value is false .

If T is an incomplete class type, the behavior is undefined.

If the program adds specializations for std::is_final or std::is_final_v (since C++17) , the behavior is undefined.

Template parameters

T - a type to check

Helper variable template

template < class T >
constexpr bool is_final_v = is_final < T > :: value ;
(since C++17)

Inherited from std:: integral_constant

Member constants

value
[static]
true if T is a final 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 >

Notes

std::is_final is introduced by the resolution of LWG issue 2112 .

A union can be declared final (and std::is_final will detect that), even though unions cannot be used as bases in any case.

Feature-test macro Value Std Feature
__cpp_lib_is_final 201402L (C++14) std::is_final

Example

Run this code 
#include <type_traits>
 
class A {};
static_assert(std::is_final_v<A> == false);
 
class B final {};
static_assert(std::is_final_v<B> == true);
 
union U final
{
    int x;
    double d;
};
static_assert(std::is_final_v<U> == true);
 
int main()
{
}

See also

(C++11)
checks if a type is a non-union class type
(class template)
(C++11)
checks if a type is a polymorphic class type
(class template)
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