What is the mutable keyword in C++?

What is the mutable keyword in C++?

The mutable keyword in C++ allows a member of a class to be modified even if the containing object is const.

Can you give me an example of how to use mutable?

Sure! Here's a simple example:

class Example {
public:
    mutable int counter;
    Example() : counter(0) {}
    void increment() const {
        counter++;
    }
};

In this case, counter can be modified in the increment method, even though it's a const method.

Why would I want to use mutable?

Using mutable is useful when you want to allow certain members to change while keeping the rest of the object immutable, like caching or tracking state.

Are there any downsides to using mutable?

Yes, overusing mutable can lead to code that is harder to understand and maintain, as it breaks the const-correctness principle.