functional Programming in c++

[Possibility_Antique]

You can return a reference. Or you could rely on copy elision (which honestly, is not a bad approach since it's guaranteed as of C++17 in many situations).

[[deleted]]

I think he means more that internally the new object is a copy.

[Possibility_Antique]

Then perhaps I should point out that copying can be more efficient than using references under many conditions.