resource with lifetime

[dvic]

Is it possible to have a resource that hands out another resource bound by the lifetime of the first resource? It seems I can't work with lifetimes at all when defining resources.

In my specific usecase I'm trying to return an iterator (a resource) from a RocksDB instance (a resource), and the lifetime of the iterator is tied to the lifetime of the RocksDB instance.

[filmor]

Could you show a bit of code to clarify what you would like to do? Lifetimes of ResourceArc objects is tied to the lifetime of the given Erlang environment, I'm not sure how one could even express what (I think) you want in Rust.

[dvic]

Sure: I'm trying to get the rocker library up to date. Here are the two resources: Vonmo/rocker@master...dvic:rocker:dvic-bump-deps#diff-f7a3db49ff9c7d28c32196b4004f0b12a096c155a3b68e157d627b19cc6bbe76R25-R32

Obviously that can't be 'static but that's the issue i'm running into. The iterator function (Vonmo/rocker@master...dvic:rocker:dvic-bump-deps#diff-f7a3db49ff9c7d28c32196b4004f0b12a096c155a3b68e157d627b19cc6bbe76R311) is where the iterator resource is created and then it's queried using the next function (Vonmo/rocker@master...dvic:rocker:dvic-bump-deps#diff-f7a3db49ff9c7d28c32196b4004f0b12a096c155a3b68e157d627b19cc6bbe76R372).

What is the recommended pattern here? When you want to expose an iterator interface and the library in question has a lifetime on the iterator :)

[dvic]

And the reason it's tied to the DB instance is because iterator eventually contains a DBRawIteratorWithThreadMode and that one uses phantom data to signal the lifetime link: https://docs.rs/rocksdb/latest/src/rocksdb/db_iterator.rs.html#73-87

[filmor]

Not sure whether that is a good idea, but you can theoretically have Iterator include a ResourceArc member which will ensure that the DB is definitely alive while the Iterator is alive. That way it should be safe to use unsafe blocks to create the iterator reference.

[dvic]

But would the IteratorResource then have a lifetime on the struct definition?