Scott answers reader questions about whether std::move is superfluous... couldn't one size of std::forward fit well enough on everyone?

On the Superfluousness of std::move

Scott Meyers

During my presentation of "Universal References in C++11" at C++ and Beyond 2012, I gave the advice to apply std::move to rvalue reference parameters and std::forward to universal reference parameters.  In this post, I'll follow the convention I introduced in that talk of using RRef for "rvalue reference" and URef for "universal reference."

Shortly after I gave the advice mentioned above, an attendee asked what would happen if std::forward were applied to an RRef instead of std::move.  The question took me by surprise.  I was so accustomed to the RRef-implies-std::move and URef-implies-std::forward convention, I had not thought through the implications of other possibilities.  The answer I offered was that I wasn't sure what would happen, but I didn't really care, because even if using std::forward with an RRef would work, it would be unidiomatic and hence potentially confusing to readers of the code.

The question has since been repeated on stackoverflow, and I've also received it from attendees of other recent presentations I've given.  It's apparently one of those obvious questions I simply hadn't considered.  It's time I did.

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