c++ overloading stream operator, parameters by reference and anonymous instances

Question

If I have a POD with an overloaded stream operator:

struct Value{
...
    friend ostream& operator<< (ostream &out, Value &val);
...
};


        

Answer 1

Since the operator should not modify the right operand, it should take it by const reference:

friend ostream& operator<< (ostream &out, const Value &val);

const references can bind to temporaries, so it will work (and that's how the standard library does it as well).