Question

I am using a member variable and at some point of the program I want to change it, but i prefer to “lock it” everywhere else to prevent unintended changes.

Code to explain:

class myClass {
    int x;  // This should be prevented to being changed most of the time
    int y;  // Regular variable
    myclass() {x = 1;}
    void foo1 () {x++; y++;} // This can change x
    void foo2 () {x--; y--;} // This shouldn't be able to change x
                             // I want it to throw a compile error
};

The question is: Can it be achieved in some way? Something like permanent const_cast?

I know I could use constructor initialization list and constant right away, but i need to change my variable later.

Answer 1

Alright, all the other answers I dislike, so here’s my idea: hide the variable.

#define READONLY(TYPE, VAR) const TYPE& VAR = this->VAR //C++03
#define READONLY(VARIABLE) const auto& VARIABLE = this->VARIABLE //C++11

class myClass {
    int x;  // This should be prevented to being changed most of the time
    int y;  // Regular variable
    myClass() :x(1), y(2) {}
    void foo1 () {// This can change x
        x++; 
        y++;
    } 
    void foo2 () {// This shouldn't be able to change x
        READONLY(x); //in this function, x is read-only
        x++; //error: increment of read-only variable 'x'
        y++;
    } 
};

There are still ways to bypass the locking of the variable (such as this->x), but nothing can be done for those situations.