cc @jckarter, @DougGregor

As a workaround, you can do result as! PHFetchResult<AnyObject> to force the type change. Dynamic-casting ObjC objects only checks the class, not the generic parameters (which don't exist at runtime).

We had a report that the as.

Another alternative is to jump up to AnyObject and then back down to the new type.

@belkadan I noticed that that seemed to quiet the compiler in a "baby" demo example, but in my real app it crashes compiler (Command failed due to signal: Illegal instruction: 4). @jckarter Same problem with unsafeBitCast.

Thanks for the heads up @mattneub. Let me see if I can whip up a fix for both as! and unsafeBitCast real quick.

@mattneub Are you able to attach your "real" app, or something like it that reproduces the crash? I just gave a naive example a whirl and wasn't able to crash it.

For reference, I just tried this, and couldn't get it to crash:

  func test(list: PHCollectionList, change: PHChange) {
    let fetched =  PHAssetCollection.fetchCollections(in: list, options: nil)
    
    change.changeDetails(for: fetched as! PHFetchResult<AnyObject>)
    
  }

@jckarter You're right, I'm wrong. The compiler crash was caused by a different bug: we can't subscript a PHFetchResult. I'll file that separately.

Looks like we have that internally: specifically, accessing a method or property that takes or returns a bridged type based on the generic parameter (like Array, Set, or Dictionary) causes the failure. (Thanks for helping look into this, @rjmccall.)

Is this resolved, or no longer valid? If either, this should be closed.

Looks invalid to me. The important one is https://bugs.swift.org/browse/SR-1576