Can you explain what a constructor with the keyword const in C++ is?

In C++, a constructor with the const keyword as such does not exist. However, there is the concept of constant constructors in other languages, such as Dart (used in Flutter). In C++, you can declare constant methods (with the const keyword after the parameter list), which do not modify the object's state.

Speaking about C++, a constructor cannot be const because it initializes the object. But you can create objects as const, and then only call constant methods.

Example of a constant method in C++:

class MyClass {
    int value;
public:
    MyClass(int v) : value(v) {}
    int getValue() const { // constant method
        return value;
    }
};

const MyClass obj(10);
int val = obj.getValue(); // permissible

If the question is about Flutter/Dart, then a const constructor allows creating immutable objects that are compiled into compile-time constants, which improves performance and saves memory.