This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 108i. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2022-07-16


2126. Lifetime-extended temporaries in constant expressions

Section: 7.7  [expr.const]     Status: C++20     Submitter: Richard Smith     Date: 2015-05-20

[Adopted as a DR at the November, 2019 meeting.]

Consider an example like the following:

  typedef const int CI[3];
  constexpr CI &ci = CI{11, 22, 33};
  static_assert(ci[1] == 22, "");

This is ill-formed because the lifetime of the array temporary did not start within the current evaluation. Perhaps we should treat all lifetime-extended temporaries of const-qualified literal type that are initialized by constant expressions as if they are constexpr objects?

Proposed resolution (October, 2019):

Change 7.7 [expr.const] paragraph 3 as follows:

A variable is usable in constant expressions after its initializing declaration is encountered if it is a constexpr variable, or it is a constant-initialized variable of reference type or of const-qualified integral or enumeration type. An object or reference is usable in constant expressions if it is

This resolution also resolves issue 2439.