Read-only stores are store where it is only possible to read existing values.
find t k is
Some v if
k is associated to
k is not present in
Write the contents of a value to the store, and obtain its key.
add but allows specifying the value's hash directly. The backend might choose to discard that hash and/or can be corrupt if the hash is not consistent.
Indexing maps the hash of a value to a corresponding key of that value in the store. For stores that are addressed by hashes directly, this is typically
fun _t h -> Lwt.return (Key.of_hash h); for stores with more complex addressing schemes,
index may attempt a lookup operation in the store.
In general, indexing is best-effort and reveals no information about the membership of the value in the store. In particular:
index t hash = Some keydoesn't guarantee
mem t key: the value with hash
hashmay still be absent from the store;
index t hash = Nonedoesn't guarantee that there is no
mem t keyand
Key.to_hash key = hash: the value may still be present in the store under a key that is not indexed.
module Val : sig ... end