On Tue, Feb 19, 2019 at 4:00 AM Jakub Jelinek <ja...@redhat.com> wrote: > On Mon, Feb 18, 2019 at 03:01:14PM -1000, Jason Merrill wrote: > > But it's not clear to me that the standard actually allows this. I don't > > think changing the active member of a union in the mem-initializer for > > another member is reasonable. > > There is in [expr.const]/2: > > an lvalue-to-rvalue conversion (7.1) that is applied to a glvalue that refers > to a non-active member of a > union or a subobject thereof; > > an assignment expression (8.18) or invocation of an assignment operator > (15.8) that would change the > active member of a union; > > in C++17 it seems, so maybe my union testcases are accepts-invalid. > This has been introduced in P0137R1 and removed again in P1330R0. Does that > mean e.g. following is valid in C++14, invalid in C++17 and valid again in > C++20? Or has one of the above papers changed retroactively previous > standards?
Before P0137 I believe foo and bar were arguably undefined. Jason
