[swift-evolution] [swift-evolution-announce] [Review] SE-0125: Remove NonObjectiveCBase and isUniquelyReferenced

[Dave Abrahams]

on Wed Jul 20 2016, Brent Royal-Gordon <brent-AT-architechies.com> wrote:

>> On Jul 19, 2016, at 11:06 PM, Dmitri Gribenko via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> - I find it a little strange to see a mention of Objective-C, and a
>> negation in `isUniquelyReferencedNonObjC`.  For example, if we get C++
>> import, would we need to rename it to
>> `isUniquelyReferencedNonObjCAndNonCXX`?  I think that is the issue
>> with negation.  If we want to emphasize that the API will work only
>> with Swift types, we can do something
>> `isUniquelyReferencedSwiftReference`.  But I would probably suggest
>> that we just go with just `isUniquelyReferenced` and mention the
>> Swift-only requirement in the documentation.
>
> I agree.
>
> What is the reason that isUniquelyReferenced(_:) doesn't work with
> Objective-C? It doesn't seem like it'd be difficult to implement—you'd
> either call -retainCount, or get it from the Objective-C runtime
> somehow, and then test it against 1—so I assume there's a reason we
> don't.

There is; it's basically impossible to implement reliably given the
state of Objective-C reference-counting.  I'll let Greg Parker explain
the details, as he has many times to me (but I don't retain them as well
as he does).

> I ask because knowing that may help us figure out how to name it. For
> instance, if the issue is that we can't rely on Objective-C reference
> counts, we might reverse the sense of the call and name it
> `mayBeShared(_:)` or `mayHaveOtherReferences(_:)`.

-- 
Dave