Jonathan M Davis:
The problem is casting. It's not uncommon to create something as mutable and then cast it to immutable when done. It's stuff like that screws with being able to per-thread GCs. Which thread owns what isn't always clear.
I nearly never cast mutables to immutable. The purpose of casts is to subvert the type system. If you accept that some type system assumption doesn't hold just because casts exist, then you are doomed to ignore every kind of type system assumption, like immutability, safety, purity, nothrowness, and so on. And this is so wrong. So I can't accept your justification that the existence casts disallow per-thread GCs. Do not use cast that way, and give us a "better" GC.
Bye, bearophile
