John McCall 945011d39f Handle default actors by special-casing layout in IRGen instead ...

of adding a property.

This better matches what the actual implementation expects,
and it avoids some possibilities of weird mismatches.  However,
it also requires special-case initialization, destruction, and
dynamic-layout support, none of which I've added yet.

In order to get NSObject default actor subclasses to use Swift
refcounting (and thus avoid the need for the default actor runtime
to generally use ObjC refcounting), I've had to introduce a
SwiftNativeNSObject which we substitute as the superclass when
inheriting directly from NSObject.  This is something we could
do in all NSObject subclasses; for now, I'm just doing it in
actors, although it's all actors and not just default actors.
We are not yet taking advantage of our special knowledge of this
class anywhere except the reference-counting code.

I went around in circles exploring a number of alternatives for
doing this; at one point I basically had a completely parallel
"ForImplementation" superclass query.  That proved to be a lot
of added complexity and created more problems than it solved.
We also don't *really* get any benefit from this subclassing
because there still wouldn't be a consistent superclass for all
actors.  So instead it's very ad-hoc.

2020-12-02 18:47:13 -05:00

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