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

[Arnold Schwaighofer]

> On Jul 19, 2016, at 11:06 PM, 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`?  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.

isUniquelyReferencedNonObjC checks that the object is a uniquely referenced swift only class. It works on non- at objc classes but will return false: The API will work for @objc-classes but return false.

The reason for this combination is data structures like Array which might hold an objc class which is not mutable. On a mutating operation you check is it uniquely reference and a swift class - if the answer is yes and you have enough storage you store to the current instance.

  expectTrue(isUniquelyReferencedNonObjc(SwiftKlazz()))
  expectFalse(isUniquelyReferencedNonObjc(ObjcKlazz()))
  var y = SwiftKlazz()
  var z = [Any]
  z.append(y)
  z.append(y)
  expectFalse(isUniquelyReferencedNonObjc(y)

The simplification of this proposal just to remove the variant that had the NonObjectiveCBase prerequisite.



> 
> - 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?

Okay I think isBufferUniquelyReferenced is good. I’ll add that change to the proposal.


> 
> 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.

No we don’t one. . We have not exposed pinning outside of the standard library (because we don’t have a design for it).

I will remove it.

> 
> Dmitri
> 
> -- 
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/