Full name of submitter (unless configured in github; will be published with the issue): Hubert Tong

Reference (section label): [class.temporary]

Link to reflector thread (if any): N/A

Issue description:
CWG 2894 will clarify that RefType{} produces a glvalue (instead of a prvalue). Once that happens, [class.temporary] will require an update to allow lifetime-extension of any temporary bound to the reference initialized by the function-style cast expression. In particular, the function-style cast is not mapped to static_cast, etc. in this case and the temporary materialization occurs within the initialization for the reference formed by the cast itself.

Implementations appear to agree already that such lifetime-extension occurs (https://godbolt.org/z/EWczhzaf6):

int glob;
struct A {
  constexpr ~A() { p = &glob; }
  int *p;
};
constexpr int f() {
  typedef const A &AR;
  const A &ref = AR{0};
  delete ref.p;
  return 0;
}
extern constexpr int x = f();  // okay

Suggested resolution:
Add a bullet to [class.temporary]/6:

• a

  • const_cast ([expr.const.cast]),
  • [ ... ]

  [ ... ]

• a function-style cast to a reference type where the reference is

  • bound directly to a glvalue operand that is one of these expressions
  • or bound to the result of a temporary materialization conversion