Example applications of overloading the assignment operator

Question

I hope this isn't seen "primarily opinion based" or "too broad". It's fairly straight forward question:

What are some example problems to which overloading the assignment operator offers a solution?

I don't think I've yet seen a situation in which it would be useful, especially considering the negative implications of having a program full of surprise implicit behaviours and "smoke and mirrors".

Answer 1

Example:

struct X
{
    int *p;
    X(): p{new int[42]}
    ~X() { delete p; }
};

What will happen if you do

X x, y;
x = y;

? The default assignment operator will copy the raw pointer, and you'll end up delete-ing the same pointer twice by the destructors of x and y. In fact, you'd better declare a copy constructor here too (or, even better, use smart pointers). Note that in

X x = some_obj;

the copy constructor is invoked (or elided if the rhs is a prvalue). The assignment operator is invoked only after construction, when you say

x = some_other_obj; // x is already constructed here

If you ask whether the operator= should exist at all (in contrast to e.g. Java), then it's probably a matter of personal preference.