This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-11-19


2922. constexpr placement-new is too permissive

Section: 7.7  [expr.const]     Status: ready     Submitter: Brian Bi     Date: 2024-07-10

constexpr placement new requires (just) pointer-interconvertibility for the argument pointer, whereas static_cast from void* to T* requires similarity. Requiring pointer-interconvertibility would not allow to differentiate two members of some union of the same type; such differentiation is required diagnose access to inactive union members.

Proposed resolution (approved by CWG 2024-08-16):

Change in 7.7 [expr.const] bullet 5.18.2 as follows:

CWG 2024-11-19

The proposed resolution does not address the ambiguity with different union members of the same type, but is a good fix to increase consistency with static_cast regardless.