P2255 A type trait to detect reference binding to temporary

[wg21bot]

P2255R0 A type trait to detect reference binding to temporary (Tim Song)

[wg21bot]

P2255R1 A type trait to detect reference binding to temporary (Tim Song)

[jfbastien]

EWG saw the paper in today's telecon.

Send P2255r1 to LEWG, with a recommendation to send it to Electronic Polling with the currently specified semantics. Only do so if LEWG agrees that the type traits as specified are useful and usable for pair, tuple, and function.

SF	F	N	A	SA
3	9	0	0	0

[inbal2l]

A short summary of the comments from LEWG's Mailing list:

• std::tuple<const std::string&> x("hello"); is ill-formed, but the usage f(tuple<const string&>("hello")) seems desirable
  Author: I lean toward defining the ctor as deleted, so that the example is still rejected. tuple<const string&>("hello"s) (or the equivalent std::string("hello")) remains available.
• Worried about false positives the trait may produce.
  Author: It produces an inevitably-dangling reference with tuple as specified today. Whether we go on to produce a likely-dangling reference or just reject the code outright seems like a somewhat separate decision to me; either way, it doesn't affect any existing valid C++20 code.

R1 is ready for LEWG Telecon.