[Issue 13537] Unions may break immutability

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13537

--- Comment #2 from hsteoh at quickfur.ath.cx ---
Unfortunately, fixing this may prove to be a challenge, because
std.typecons.Rebindable uses a union of (possibly) immutable and mutable fields
in order to achieve rebindability. Arguably, though, some kind of explicit cast
ought to be required in that case.  Either that, or we impose the
non-overlapping restriction only in @safe code, so that @system code can
continue using unions to do black magic with immutability.

--