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

[Arnold]

Sent from my iPhone

> On Jul 20, 2016, at 12:47 PM, Dave Abrahams <dabrahams at apple.com> wrote:
> 
> 
> on Wed Jul 20 2016, Arnold Schwaighofer <aschwaighofer-AT-apple.com> wrote:
> 
>>> On Jul 20, 2016, at 9:54 AM, Andrew Trick <atrick at apple.com> wrote:
>>> 
>>> 
>>>> On Jul 20, 2016, at 9:44 AM, Arnold Schwaighofer <aschwaighofer at apple.com> wrote:
>>>> 
>>>> 
>>>> The question is are they relying on the non- at objc post-condition
>>>> when the API returns true? If they were to implement something like
>>>> array they might.
>>> 
>>> The conservative thing to do is not make that promise for now and
>>> address need later if it’s important. Conservative makes sense to me
>>> given the current level of confusion.
>> 
>>>>> 
>>>>> That said, something like “isUniquelyReferencedNativeSwift” would
>>>>> work assuming that’s semantically correct (“native" Swfit objects
>>>>> do not inherit from NSObject). “isKnownUniquelyReferenced” would
>>>>> be fine with a warning in the doc comment that it may always
>>>>> return false for objc objects.
>>>> 
>>>> 
>>>> Native swift objects are the ones that use native swift reference
>>>> counting and don’t alias Objc class instances. That is at least how
>>>> we have defined it at the SIL (Builtin.NativeObject vs
>>>> Builtin.UnknownObject) level:
>>>> 
>>>> 
>>>> * A ``Builtin.NativeObject`` may alias any native Swift heap object,
>>>> including a Swift class instance, a box allocated by ``alloc_box``,
>>>> or a thick function's closure context.
>>>> It may not alias natively Objective-C class instances.
>>>> 
>>>> 
>>>> I think at the language/stdlib level the “native” concept is
>>>> implementation detail that is not witnessed other than with the
>>>> non- at objc requirement of ManageBufferPointer and
>>>> isUniquelyReferencedNonObjC, i.e at the language/stdlib level we
>>>> call “native” "non- at objc”. Which IMO is more descriptive.
>>> 
>>> I totally agree, but people can’t have it both ways. You can’t avoid
>>> a negative in the name and refuse to define the positive
>>> nomenclature.
>>> 
>>>> I understand the desire to remove Objc’ness from API names that can be used on platforms without ObjC.
>>> 
>>> Me too.
>>> 
>>> +1 forisKnownUniquelyReferenced, with clarifying doc comments
>> 
>> Do we continue promise that “isKnownUniquelyReferenced” returns false
>> for non- at objc objects in the comments?
> 
> I think you mean, “do we promise that “isKnownUniquelyReferenced” returns
> false for @objc objects?”

Yes.

> 
> IMO we should not make that promise.  There's not much you can do with it.


You can implement Array (or a similar bridged) type outside of the standard library -- at least the aspect of it that transitions to a native representation when you write to it if it is non-native.

I am fine with dropping the promise, though.