Ever wondered how can you design a class in C++ which can’t be inherited. Java and C# programming languages have this feature built-in. You can use final keyword in java, sealed in C# to make a class non-extendable.
Below is a mechanism using which we can achieve the same behavior in C++. It makes use of private constructor, virtual inheritance and friend class.
In the following code, we make the Final class non-inheritable. When a class Derived tries to inherit from it, we get compilation error.
An extra class MakeFinal (whose default constructor is private) is used for our purpose. Constructor of Final can call private constructor of MakeFinal as Final is a friend of MakeFinal .
Note that MakeFinal is also a virtual base class. The reason for this is to call the constructor of MakeFinal through the constructor of Derived, not Final (The constructor of a virtual base class is not called by the class that inherits from it, instead the constructor is called by the constructor of the concrete class).
Output: Compiler Error
In constructor 'Derived::Derived()': error: 'MakeFinal::MakeFinal()' is private
In the above example, Derived‘s constructor directly invokes MakeFinal’s constructor, and the constructor of MakeFinal is private, therefore we get the compilation error.
You can create the object of Final class as it is friend class of MakeFinal and has access to its constructor. For example, the following program works fine.
Output: Compiles and runs fine
MakeFinal constructor Final constructor
This article is compiled by Gopal Gorthi and reviewed by GeeksforGeeks team. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.
- C++ final specifier
- Difference between Base class and Derived class in C++
- How to convert a class to another class type in C++?
- std::any Class in C++
- Array class in C++
- std::string class in C++
- std::hash class in C++ STL
- Structure vs class in C++
- std:: valarray class in C++
- Virtual base class in C++
- How to implement our own Vector Class in C++?
- What all is inherited from parent class in C++?
- Difference between namespace and class
- C++ String Class and its Applications | Set 2
- C++ string class and its applications
- Why is the size of an empty class not zero in C++?
- Can a C++ class have an object of self type?
- Friend class and function in C++
- std::is_trivially_copy_assignable class in C++ with Examples
- C++ | Class and Object | Question 6