[MarkPNeyer]

the class list would be rendered by looking up the teacher's name. a rendering can be cached with a timestamp (it was valid as of this time) and then the most recent render can be stored. by setting a dirty flag whenever data changes, you can update dependencies when they are fetched and then memoize the results.

[seanmcdirmid]

You still need consistent object identities to do that, which are then tantamount to mutability (they are equivalent with equivalent problems related to consistency, and similar solutions).

[MarkPNeyer]

can you elaborate?