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

Arnold aschwaighofer at apple.com
Wed Jul 20 10:15:58 CDT 2016

Sent from my iPhone

> On Jul 20, 2016, at 6:50 AM, Dave Abrahams <dabrahams at apple.com> wrote:
>> on Tue Jul 19 2016, Dmitri Gribenko <gribozavr-AT-gmail.com> wrote:
>>> On Tue, Jul 19, 2016 at 10:51 PM, Chris Lattner <clattner at apple.com> wrote:
>>> The review of "SE-0125: Remove NonObjectiveCBase and
>>> isUniquelyReferenced" begins now and runs through July 22. The
>>> proposal is available here:
>>>        https://github.com/apple/swift-evolution/blob/master/proposals/0125-remove-nonobjectivecbase.md
>> I like the API simplification.  A few thoughts that I have after
>> reading the proposal that could take the simplification it even
>> further:
>> - 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`?  
> Only if we were unable to determine that CXX imports were
> uniquely-referenced.
>> 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`.  
> That's not really the point.  The point is to find out whether it's
> *known* to be a unique reference.  False negatives are part of the
> game.
>       isKnownUniquelyReferenced
> would work.

This would be a change to the semantics of the API. Currently, you can rely on -- and is documented as -- that if it returns true you can assume the reference points to a non- at objc instance.

Users may be relying on this behavior.

Do we want to add an isNativeSwiftReference API?

>> But I would probably suggest that we just go with just
>> `isUniquelyReferenced` and mention the Swift-only requirement in the
>> documentation.
> It's not a requirement, as in “precondition.”  The point of having
> `NonObjC` in this API is actually that it *does* work on ObjC
> references, by returning false.
>> - I find the use of different names in `isUniquelyReferenced()` and
>> `ManagedBufferPointer.holdsUniqueReference()` to be strange.  Why not
>> call the latter `ManagedBufferPointer. isUniquelyReferenced()`?  It is
>> true that we are not checking that pointer is not uniquely referenced,
>> if we want to emphasize that, maybe something like
>> `ManagedBufferPointer.isBufferUniquelyReferenced()` or
>> `isPointeeUniquelyReferenced()` will work?
>       isUniqueReference
> would work for ManagedBufferPointer.
>> The reason why I'm suggesting this is that `isUniquelyReferenced` and
>> `holdsUniqueReference` don't immediately strike me as performing the
>> same operation, the immediate impression I get is that these
>> operations are related, but subtly different, and it is not obvious
>> what the difference is (but after reading the docs I figure out that
>> there is no difference... until I need to use these APIs again).
>> - We have `ManagedBufferPointer.holdsUniqueOrPinnedReference()`, but
>> don't have an equivalent free function `isUniquelyReferencedOrPinned`
>> (we actually have one, but it is internal).  Do we need a public one?
>> If we do, we could as well add it as a part of this proposal, while we
>> are cleaning up this library subsystem.
> Maybe, but it's not crucial.
> -- 
> Dave

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