What are abstract classes in C++20?

What are abstract classes in C++20?

Abstract classes in C++20 are classes that cannot be instantiated and are meant to be subclassed. They contain at least one pure virtual function.

Can you give me an example of an abstract class?

Sure! Here's a simple example:

class Shape {
public:
    virtual void draw() = 0; // Pure virtual function
};

In this example, Shape is an abstract class because it has a pure virtual function draw().

How do I implement an abstract class?

To implement an abstract class, you need to create a derived class that overrides the pure virtual functions. For example:

class Circle : public Shape {
public:
    void draw() override {
        // Implementation for drawing a circle
    }
};

What happens if I don't implement the pure virtual function?

If you don't implement the pure virtual function in the derived class, that derived class will also be considered abstract and cannot be instantiated.