Can we use the return value optimization when possible and fall back on move, not copy, semantics when not?

Question

Is it possible to write C++ code where we rely on the return value optimization (RVO) when possible, but fall back on move semantics when not? For example, the following code c

Answer 1

Yes, there is. Don't return the result of a ternary operator; use if/else instead. When you return a local variable directly, move semantics are used when possible. However, in your case you're not returning a local directly -- you're returning the result of an expression.

If you change your function to read like this:

Foo f(bool b) {
    Foo x;
    Foo y;
    if (b) { return x; }
    return y;
}

Then you should note that your move constructor is called instead of your copy constructor.

If you stick to returning a single local value per return statement then move semantics will be used if supported by the type.

If you don't like this approach then I would suggest that you stick with std::move. You may not like it, but you have to pick your poison -- the language is the way that it is.