[swift-dev] How should NSArray<void(^)(void)>* be imported?

[Joe Groff]

> On Mar 3, 2016, at 10:26 AM, Jacob Bandes-Storch <jtbandes at gmail.com> wrote:
> 
> Is another hack the way to go, or should it be correctly imported as [@convention(block) () -> ()] (which I think would be _isBridgedToObjectiveC already)?

Bridging to @convention(block) is probably more practical, since we'd otherwise need to be able to thunk an arbitrary call signature at runtime. However, @convention(block) is still a structural type, so it would need special case handling similar to _BridgeableMetatype to be able to feed a _BridgedToObjectiveC conformance into the runtime.

-Joe

> 
> On Thu, Mar 3, 2016 at 9:08 AM, Joe Groff <jgroff at apple.com <mailto:jgroff at apple.com>> wrote:
> 
>> On Mar 3, 2016, at 2:23 AM, Jacob Bandes-Storch via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>> 
>> I'm interested in fixing a pet peeve of mine: https://bugs.swift.org/browse/SR-772 <https://bugs.swift.org/browse/SR-772>
>> 
>> The failing assertion is in Array._forceBridgeFromObjectiveC, namely Swift._isBridgedToObjectiveC(Element.self). Element is plain ol "() -> ()", but probably should be @convention(block) since it was imported from void(^)(void).
>> 
>> I've started tracing through the importer, and I found that `adjustTypeForConcreteImport` is enforcing FunctionTypeRepresentation::Swift because the ImportKind is BridgedValue — this is hardcoded in the call to importType for the type parameters to NSArray (and NSDictionary and NSSet) in SwiftTypeConverter::VisitObjCObjectPointerType.
>> 
>> Are the Foundation collection classes only temporarily special-cased here, until Obj-C generics are generally supported? Is someone working on this in the near future?
>> 
>> If this worked correctly, would we expect to see "var executionBlocks: [@convention(block) () -> ()]" ? If so, would this be best achieved by passing a different ImportKind, possibly introducing a new ImportKind, or some other solution?
>> 
>> I'm guessing that it doesn't make sense for () -> () to be _ObjectiveCBridgeable, but either way I'm not sure where the _isBridgedToObjectiveC implementation for blocks would come from.
>> 
>> Bumblingly,
>> Jacob
> 
> There's a hack to handle NSArray<Class> * bridging to [AnyObject.Type], which has similar problems. Look around for _BridgeableMetatype.
> 
> -Joe
> 
> 

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