Ssreg,
Unfortunately this is official:
You can subclass a generic class, but the subclass must also be a
generic class.
Let us hope Apple fixes this in a future version.
Meanwhile, let us see this as an opportunity to exploit aggregation instead of subclassing.
NOTE:
As a poor man’s version of a solution, one could use typealias:
class foo<T> {}
class bar<Int> : foo<Int> {}
typealias Bar = bar<Int>
This way, the rest of the code can be written just as if Apple already fixed the matter.