Did you look at the generated assembly of your demo? RVO probably didn't happen there. "returns_a_foo" was most likely inlined into main and then there was no n

Did you look at the generated assembly of your demo? RVO probably didn't happen there. "returns_a_foo" was most likely inlined into main and then there was no need of eliding a copy. I'm not saying that you are wrong, only that your demo poorly demonstrates what you are arguing.