Rethink the Deletable abstraction

[concordium]

Rethink the Deletable abstraction

[target-san]

Oh, thx very much. Now this makes perfect sense.

[target-san]

@abizjak Can you please point to some arguments why Deletable instead of just Drop? From my POV former requires no arguments, like destruction context, and causes resource leak when not invoked properly. So it looks exactly like Drop, just manual.

[abizjak]

Deletable solves a different problem than Drop. Deletable applies to things in the contract's persistent state, i.e., the state that survives across contract updates.

In contrast, Drop is to clean up transient resources, i.e., a vector allocated in memory. This cleans up/deallocates the memory that is used during a single contract call.

The persistent state is like a database. Using Drop would be akin to deleting the value in the database because we dropped the handle to it from the program. That is typically not what you want to do.

Did this make sense?