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package irmin
An indexable store is a read-write store in which values can be added and later found via their keys.
Keys are not necessarily portable between different stores, so each store provides an index mechanism to find keys by the hashes of the values they reference.
Parameters
module S : Content_addressable.S with type key = Key.tSignature
Read-only stores
Read-only stores are store where it is only possible to read existing values.
type 'a t = 'a S.tThe type for stores. The 'a phantom type carries information about the store mutability.
type key = Key.tThe type for keys.
type value = S.valueThe type for raw values.
val mem : [> Perms.read ] t -> key -> bool Lwt.tmem t k is true iff k is present in t.
val find : [> Perms.read ] t -> key -> value option Lwt.tfind 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.
type hash = Key.tThe type of hashes of value.
val add : [> Perms.write ] t -> value -> key Lwt.tWrite the contents of a value to the store, and obtain its key.
Same as 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.
val index : [> Perms.read ] t -> hash -> key option Lwt.tIndexing 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 guaranteemem t key: the value with hashhashmay still be absent from the store;
index t hash = Nonedoesn't guarantee that there is nokeysuch thatmem t keyandKey.to_hash key = hash: the value may still be present in the store under a key that is not indexed.
val batch :
Perms.read t ->
([ Perms.read | Perms.write ] t -> 'a Lwt.t) ->
'a Lwt.tbatch t f applies the writes in f in a separate batch. The exact guarantees depend on the implementation.
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