How function chaining is working without T& as return type of operator + and =

Question

Please refer code below:
It works fine but I am concerned about how it is working ok without complex& for operator +
As this would be calling unnecessary copy constructor twice for c123, how to do complex& for operator +?
https://code.sololearn.com/cLmSIBW4NoFS/?ref=app
P.s. : + should not be considered as complex& and I got that point.... Why = also working without complex& operator= for c12 = c123 = c2?

Answer 1

operator+ cannot have complex& as the return type for an obvious reason(you shouldn't return an lvalue reference to a local variable)
For operator=, no. The copy constructor won't be called twice because of return value optimization(RVO).
Search for it on the web for more details.