The type for stores. The 'a phantom type carries information about the store mutability.

The type for keys.

The type for raw values.

mem t k is true iff k is present in t.

find t k is Some v if k is associated to v in t and None is k is not present in t.

close t frees up all the resources associated with t. Any operations run on a closed handle will raise Closed.

The type of hashes of value.

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 key doesn't guarantee mem t key: the value with hash hash may still be absent from the store;

• index t hash = None doesn't guarantee that there is no key such that mem t key and Key.to_hash key = hash: the value may still be present in the store under a key that is not indexed.

batch t f applies the writes in f in a separate batch. The exact guarantees depend on the implementation.