Using move semantics for a cast operator

Question

Suppose I have two classes foo, and bar that are fairly well-related, by which I mean that they contain common data members.

I have a cast operator operator bar() const; in the foo class.

I also have a function func that takes a bar.

If I call func with an anonymous temporary foo then the cast operator will be called. But as I don't need the foo, can I declare some sort of move cast so explicitly optimising out any unnecessary copies?

Answer 1

If your compiler supports ref-qualifiers on member functions (a C++11 feature), you can:

operator bar() const &
{
  return bar(the_common_data);
}

operator bar() &&
{
  return bar(std::move(the_common_data));
}

[Live example]

Answer 2

Yes, you can using r-value this syntax:

operator bar() &&{ /* std::move(...); */ }