Shared mutability in Rust Part 2 of 3: Acyclic graphs
- Child entities which are both mutable and shared can make any, or all of their parents invalid.
- In freeform shared mutability, we cannot cache any calculation that depends on a shared mutable entity.
- If we limit the scope of sharing to code we trust not to invalidate our cache, then we can cache results as much as we like.
- Limiting the scope of sharing implies that we have some kind of container entity: an Arena.