Scoped Conformances

[jrose (Jordan Rose)]

@dabrahams

Our answer is that X’s conformance (or not) to P is captured in the scope where the X value is first converted to an existential type. If the cast occurred in the scope where a conformance of X to P is visible (in the same module as File1.swift, in this case), foo will print “P”.

Is there an implementation plan for this? Right now, the representation of an Any value does not include where it was formed. The representation of an AnyObject value that's actually a class cannot include where it was formed.

I'll probably have further thoughts on this approach in general later, but this bit seems important to clear up sooner rather than later. (I think my preferred approach would be "non-public conformances never satisfy dynamic casts".)