This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See for the official list.


2666. Lifetime extension through static_cast

Section: 6.7.7  [class.temporary]     Status: open     Submitter: Brian Bi     Date: 2022-10-17


  struct S { S(int) {} };

  const S& r1 = 0; // #1
  const S& r2 = static_cast<const S&>(S(0)); // #2
  const S& r3 = static_cast<const S&>(0); // #3
  // Are r1, r2, and r3 dangling past this point?

For #1, a temporary object is materialized and the reference binds to the result of the materialization conversion. This results in lifetime extension per 6.7.7 [class.temporary] bullet 6.1.

For #2, 6.7.7 [class.temporary] bullet 6.6 requires the cast to convert "without a user-defined conversion", but S(0) is such.

For #3, a user-defined conversion is clearly required.

However, implementations treat all three cases the same and do extend the lifetime of the temporary.

Suggested resolution:

Change in 6.7.7 [class.temporary] bullet 6.6 as follows: