The underlying std::string is freed?

Posted Jul 6, 2024 14:15 UTC (Sat) by intelfx (subscriber, #130118)
In reply to: The underlying std::string is freed? by Cyberax
Parent article: New features in C++26

> I thought that const references to temporaries extend their lifetime? I'd used that to implement scope guard in C++03.

Yes, but there was an exception: binding to a reference in a returned value did not extend the lifetime of the temporary.

In C++23 and earlier, N4950 6.7.7 [class.temporary]/6.11 stated that returned values are excluded from the lifetime-extension rule.

> The lifetime of a temporary bound to the returned value in a function return statement ([stmt.return]) is not extended; the temporary is destroyed at the end of the full-expression in the return statement.

This wording was included in the standard up to N4971.

The proposal we are discussing here (https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/...) removes that exception and instead makes such references ill-formed.

So basically the previous rule was "well-formed, but return values do not extend lifetimes, so you get a dangling reference" and it was replaced with a rule that such references are now ill-formed.