Which standard wording tells us that ref-to-const temporary lifetime extension only “works once”?

Question

I was shown the following example in chat:

#include 
struct foo { ~foo() { std::cout << \"destroying!\\n\"; } };
const foo& func(co         


        

Answer 1

This is subject of two issue reports, http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1299 and http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1568 .

The former issue report, of which I am the reporter, was intended to cover all these cases where a reference is bound to a temporary object, but is not intended to be lifetime-extending. The description in the body of the issue only mentions prvalues being confused with temporary expressions (that actually decide whether lifetime of what they evaluate to is lengthened or not). But lvalue and xvalues are likewise confused with these in the Standard. An example where that happens in the context of static_cast is issue number #1568 (in which the use of "temporary variable" further confuses the matter).

Actually, this:

A temporary bound to a reference parameter in a function call (5.2.2) persists until the completion of the full-expression containing the call.

Contradicts the other rules in the same paragraph. Because the temporary is bound to both a reference parameter in a function call and to a local automatic reference variable.