Question

Just curious about how to overload them.

The opAssign operators are like addAssign(+=) and subAssign(-=).

“globally” means they are not overloaded as member functions, but just a operator act on operands

For these opAssign operators, they are binary operators.(they receive two operands)
Therefore two parameters are needed.

I found no examples on the web…..

Answer 1

Here’s a trivial example of defining operator+=:

struct Foo{
    int x;
};

Foo& operator+=(Foo& lhs, const Foo& rhs) {
    lhs.x += rhs.x;
    return lhs;
}