There are cases where copy elision doesn't work (don't know how important is that in practice). One representative example would be something like this (I thin

There are cases where copy elision doesn't work (don't know how important is that in practice). One representative example would be something like this (I think this can't use copy-elision, but I am not an expert in C++, please correct me if I am wrong!) void f(std::vector<Foo>& xs) { xs.emplace_back(arg1, arg2); } Here, the semantics is that xs is resized first and then the constructor for Foo(arg1, arg2) is called. So, if resizing xs throws, no Foo is constructed at all. If we replace emplacement with push_back and a factory function, then the semantics becomes 1) construct Foo 2) extend the vector 3) copy/move Foo into the vector.