This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 119a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-12-20

3096. Value-dependence of size of structured binding pack with non-dependent initializer

[Accepted as a DR at the November, 2025 meeting.]

The special case for a structured binding pack introduces an unnecessary inconsistency. A structured binding pack with a non-dependent initializer should either always be instantiated early or never, regardless of the expression it is used in. The more comprehensive rule to always instantiate early was removed after R7 of the paper (P1061R7 Structured Bindings can introduce a Pack), but the special case for "sizeof ..." remained.

Proposed resolution (approved by CWG 2025-11-03):

Change in 13.8.3.4 [temp.dep.constexpr] paragraph 4 as follows:

Expressions of the following form are value-dependent:

  sizeof ... ( identifier )
  fold-expression

unless the identifier is a structured binding pack whose initializer is not dependent.