Immutability

We've already understood that a certain level of immutability is preferred in C++; the common example is as follows:

class ...{
    int add(const int& first, const int& second) const{
        return first + second;
    }
}

The const keyword clearly communicates a few important constraints on the code, such as the following:

• The function does not change any of its arguments before returning.
• The function does not change any data member of the class it belongs to.

Let's now imagine an alternate version of add, as follows

int uglyAdd(int& first, int& second){
    first = first + second;
    aMember = 40;
    return first;
}

I called this uglyAdd for a reason—I don't tolerate code like this when I'm programming! This function violates the principle of minimal surprise and does too many things. Reading the function code reveals nothing...