https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79671
--- Comment #63 from Jason Merrill <jason at gcc dot gnu.org> --- (In reply to rguent...@suse.de from comment #54) > > > > --- Comment #51 from Bernd Edlinger <bernd.edlinger at hotmail dot de> > > > > --- > > > > Doesn't 3.10/10 explicitly say that it is undefined to use a union to > > > > to move an object representation that is not a member of the union? > But still the other clause says the storage representation is transfered > and so you could read into that that no "access" happens and thus > 3.10/10 doesn't apply. Right, union copy copies the bytes of the object representation, i.e. memcpy. (In reply to Richard Biener from comment #50) > Note that what changed with GCC 7 is only that unions with char members > no longer behave as alias-set zero but 12.8/16 talks about all unions, > not just unions with char members. > > Now I read comment#14 as that _only_ char[] members (of structs or unions) > may ever "contain" different dynamic types. Any pointer to a part of > the standard that singles out char[] that way? char is special that way because it can be used to access the stored value of an object of any type (3.10/10.8). Now that C++17 introduces std::byte for this sort of thing, I hope to transition away from the permissive aliasing behavior of char.
