Question

Say we have an utility function:

std::string GetDescription() { return "The description."; }

Is it OK to return the string literal? Is the implicitly created std::string object copied?

I thought about always returning it like this:

std::string GetDescription() { return std::move(std::string("The description.")); }

But it’s of course longer and more verbose. We could also assume that compiler RVO will help us a bit

std::string GetDescription() { return std::string("The description."); }

Yet still, I don’t know what it really has to do, instead of what can it do.

Answer 1

std::string GetDescription() { return "XYZ"; }

is equivalent to this:

std::string GetDescription() { return std::string("XYZ"); }

which in turn is equivalent to this:

std::string GetDescription() { return std::move(std::string("XYZ")); }

Means when you return std::string("XYZ") which is a temporary object, then std::move is unnecessary, because the object will be moved anyway (implicitly).

Likewise, when you return "XYZ", then the explicit construction std::string("XYZ") is unnecessary, because the construction will happen anyway (implicitly).

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So the answer to this question:

Is the implicitly created std::string object copied?

is NO. The implicitly created object is after all a temporary object which is moved (implicitly). But then the move can be elided by the compiler!

So the bottomline is this : you can write this code and be happy:

std::string GetDescription() { return "XYZ"; }

And in some corner-cases, return tempObj is more efficient (and thus better) than return std::move(tempObj).