the focus here is to make it safe to have mutable data around, not to have manual memory management

This sketch is complicated by the fact that there are actually three such arenas; the CLR collector is generational. Objects start off in the “short lived” heap. If they survive they eventually move to the “medium lived” heap, and if they survive there long enough, they move to the “long lived” heap. The GC runs very often on the short lived heap and very seldom on the long lived heap; the idea is that we do not want to have the expense of constantly re-checking a long-lived object to see if it is still alive. But we also want short-lived objects to be reclaimed swiftly.