> On Apr 1, 2016, at 8:43 AM, Joe Groff via swift-dev <swift-dev@swift.org> > wrote: > > >> On Mar 31, 2016, at 11:49 PM, Patrick Pijnappel <patrickpijnap...@gmail.com> >> wrote: >> >> The modified version doesn't seem to change any of the results (on -O or >> -Onone). Note that the problem is that it's not uniquely referenced inside >> bar where it actually should be – that would mean that ownership is >> currently not directly transferred right? > > You're right, I'm sorry, I misread your original comment. If the ARC > optimizer didn't transfer ownership, then it is correct for > `isUniquelyReferenced` to be false inside `bar`, since the `foo` inside of > `test` and the `foo` parameter to `bar` are semantically independent values. > If this weren't the case, then `bar` could modify a COW value type and have > its changes be seen back in `test`'s copy.
In other words, to avoid a copy, the COW value must be passed ‘inout’. This is normally true anyway for functions that mutate the value. It would be neat to have a ‘move’ operator that handed ownership of the COW value off to the callee. But the memory safety of that would be problematic in general. -Andy _______________________________________________ swift-dev mailing list swift-dev@swift.org https://lists.swift.org/mailman/listinfo/swift-dev
