I check you change code from Rc<S> to Rc<dyn Store> . Which is from static dispatch to dynamic dispatch. I usually using dynamic dispatch only when it's cannot be determine during compile time ( because dynamic dispatch determine type during run time it takes more time ). In our case we can determine to have one store type per each mmr, is there any specific reason why you changed into dynamic dispatch?

Yes, the store is dynamic because I want the flexibility in infinitely stackable mmr to provide any stores for any mmr

And also it's just a reference to the dyn Store it's not storing the store itself