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Document number: N4164

Date: 2014-10-06

Forwarding References

by Herb Sutter, Bjarne Stroustrup, Gabriel Dos Reis

Excerpt:

To the C++ programmer, a parameter of type C&& is always an rvalue reference -- except when C is a template parameter type or auto, in which case it behaves very differently even though language-technically it is still an rvalue reference.

We intentionally overloaded the && syntax with this special case, but we did not give this special case a name. It needs a distinct name so that we can talk about it and teach it. This has already been discovered in the community, thanks to Scott Meyers in particular. [1]

In the absence of our giving this construct a distinct name, the community has been trying to make one. The one that is becoming popular is “universal reference.” [1] Unfortunately, as discussed in §3.1 below, this is not an ideal name, and we need to give better guidance to a suitable name.

The name that has the most support in informal discussions among committee members, including the authors, is “forwarding reference.” Interestingly, Meyers himself initially introduced the term “forwarding reference” in his original “Universal References” talk, [2] but decided to go with “universal references” because at the time he did not think that “forwarding references” reflected the fact that auto&& was also included; however, in §3.3 below we argue why auto&& is also a forwarding case and so is rightly included.