[PRL] POPL NOTES

[Johan Ovlinger]

> Virtual types: when you specialize subject, then you need to
> specialize observer and event classes.  Violates behavioral
> subtyping. 
> 
> KB's solution:  "mutually recursive groups"; use @ThisTG (exactly this type
> group) to get comon covariant specialization.

Huh.

I'm surprised Erik Ernst / Klaus Ostermann didn't chime it at this 
point with a pointer to family polymorphism.