> On Sep 12, 2016, at 12:24 PM, Paul Cantrell <cantr...@pobox.com> wrote: > > >> On Aug 29, 2016, at 11:14 AM, Joe Groff via swift-evolution >> <swift-evolution@swift.org> wrote: >> >>> On Aug 24, 2016, at 5:08 PM, Charles Srstka via swift-evolution >>> <swift-evolution@swift.org> wrote: >>> >>> PROPOSED SOLUTION: >>> >>> I propose the following operators: really_is, really_as, really_as?, and >>> really_as!. These operators would only return a positive result if the type >>> actually was what was being asked for, instead of something that might be >>> able to bridge to that type. >>> >>> DETAILED DESIGN: >>> >>> let foo: Any = "Foo" >>> let bar: Any = NSString(string: "Bar") >>> >>> let fooIsString = foo is String // true >>> let fooReallyIsString = foo really_is String // true >>> >>> let fooIsNSString = foo is NSString // true >>> let fooReallyIsNSString = foo really_is NSString // false >>> >>> let barIsString = bar is String // true >>> let barReallyIsString = bar really_is String // false >>> >>> let barIsNSString = bar is NSString // true >>> let barReallyIsNSString = bar really_is NSString // true >>> >>> ALTERNATIVES CONSIDERED: >>> >>> Stick with using an unholy combination of Mirror and unsafeBitCast when you >>> need to know what you’ve actually got. >> >> It would be helpful to know why you want this. What are you trying to do? > > I’ve got one: > > Siesta has a notion of “observer ownership,” whose semantics in a nutshell > are “free the observer when its owners are all deallocated.” (Details here: > http://bustoutsolutions.github.io/siesta/guide/memory/) > > Never mind the details. The important thing is that owners must be objects > because we care about the fact that they have an allocation lifecycle. > > In Swift 2, this declaration ensured that callers used only objects as owners: > > func addObserver(observer: ResourceObserver, owner: AnyObject) > > In Swift 3, however, an unsuspecting called can pass a struct as an owner. > Swift helpfully wraps it in a _SwiftValue, the _SwiftValue is only weakly > referenced so it’s immediately deallocated, and so the observer is > immediately discarded. It’s nonsensical. The compiler should be able to > detect & prevent this. > > What I want is: > > func addObserver(observer: ResourceObserver, owner: > AnyObjectForRealNotJustAValueWrapper) > > AFAIK, this is impossible in Swift 3. Or is it?
If you declare the API as taking AnyObject in Swift, this should work *better* in Swift 3, since it is no longer possible to pass non-object value types to an AnyObject API by implicit conversion. If the API came from Objective-C, and uses `id` there, you could perhaps hide the `Any` version that gets imported and drop an AnyObject-taking version on top of it in a Swift overlay. I agree that we ought to have a more general feature in ObjC to say "no, really, this needs to be a reference type", but I think that's orthogonal to Charles' original request. -Joe _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
