is_final template in C++

In this article we will be discussing the working, syntax and examples of std::is_final template in C++ STL.

is_final is a template which comes under the <type_traits> header file. This template is used to check whether the given type T is a final class or not.

What is a final class in C++?

When we declare a class with the final specifier then it is called as Final Class. Final class is a special kind of class which can’t be extended to create another class. In C++ to make a class as a final we make a class as a friend and then virtually inherit that class, to make that class nonextendable.

Example of a final class

class final_abc; //Class which is to be made final
class abc {
   private:
   abc(){cout<<"abc constructor";}
   friend class final_abc;
};
class final_abc : virtual abc //made it final class. {
   public:
   final_abc(){cout<<"Final class constructor";}
};
class derive : public final_abc; //Error can't be extended

Syntax

template <class T> is_final;

Parameters

The template can have only parameter of type T, and check whether the given type is a final class type or not.

Return value

It returns a Boolean value, true if the given type is a final class, and false if the given type is not a final class.

Example

Input: class final_abc;
   class abc { friend class final_abc; };
   class final_abc : virtual abc{ };
   is_final<abc>::value;
Output: False

Input: class final_abc;
   class abc
   { friend class final_abc; };
   class final_abc : virtual abc{ };
   is_final<final_abc>::value;
Output: True

Example

 Live Demo

#include <iostream>
#include <type_traits>
using namespace std;
class TP {
   //Same if it will be a structure instead of a class
};
class T_P final {
   //Same if it will be a structure instead of a class
};
int main() {
   cout << boolalpha;
   cout << "Using is_final";
   cout << "\nTutorials Point: "<<is_final<TP>::value;
   cout << "\nT_P Final: "<<is_final<T_P>::value;
   cout << "\ncheck for char: "<<is_final<int>::value;
   return 0;
}

Output

If we run the above code it will generate the following output −

Using is_final
Tutorials Point: false
T_P Final: true
check for char: false

Example

 Live Demo

#include <iostream>
#include <type_traits>
using namespace std;
union TP {
   //Union
};
union T_P final {
   //Union
};
int main() {
   cout << boolalpha;
   cout << "Using is_final";
   cout << "\nTutorials Point: "<<is_final<TP>::value;
   cout << "\nT_P Final: "<<is_final<T_P>::value;
   cout << "\ncheck for char: "<<is_final<int>::value;
   return 0;
}

Output

If we run the above code it will generate the following output −

Using is_final
Tutorials Point: false
T_P Final: true
check for char: false