Why reference is not needed for + operator overloading

Question

Hi

Please refer attached code for reference.

It's output is 9 which I expected. However, even if I change signature of operator + as below,
test operator+(const test& other)

It still works and gives 9 as output. Does reference return (test&) is not must for this operator and why ?
https://sololearn.com/compiler-playground/ca5VNO2jSp44/?ref=app

Answer 1

if you are mutating the value, then return by reference. if you are assigning to a new variable, then return by value.

https://stackoverflow.com/questions/2337213/return-value-of-operator-overloading-in-c

also
https://stackoverflow.com/questions/4421706/what-are-the-basic-rules-and-idioms-for-operator-overloading

Answer 2

using const reference as argument is better, I think:

test& operator+(const test& other){
m_x = m_x + other.m_x;
return *this;
}

allows you to use rvalues:

test obj1(2);
test res = test(3) + obj1;

compare this with:
test& operator+(test& other){
m_x = m_x + other.m_x;
return *this;
}

which will raise an error if you do the same:

test obj1(2);
test res = test(3) + obj1;

Answer 3

Thanks but my concern is on return type of function. Does ref return is not mandatory for + operator ?