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

Tony Parker anthony.parker at apple.com
Wed Jul 20 10:55:09 CDT 2016

For what it’s worth, I agree with Dmitri on the naming of this function. I think we should find a way to give it a name without “NonObjC” in it.

- Tony

> On Jul 20, 2016, at 8:15 AM, Arnold via swift-evolution <swift-evolution at swift.org> wrote:
> 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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