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.
2026-02-06
(From submission #706.)
Consider:
static union {
int x = [] { return 42; }();
};
According to 11.5.2 [class.union.anon] paragraph 1, this is ill-formed, because the closure type is declared as a nested type of the anonymous union (7.5.6.2 [expr.prim.lambda.closure] paragraph 3, but some implementations do not yield a diagnostic.
On the other hand, the code shown in the example is reasonable and ought to be allowed.
Proposed resolution (approved by CWG 2026-02-06):
Change in 11.5.2 [class.union.anon] paragraph 1 as follows:
... Nested types,(including closure types (7.5.6.2 [expr.prim.lambda.closure]) and anonymous unions,) and functions shall not be declared within an anonymous union....