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Module Hashtbl2


module Hashtbl2: sig  end
This module provides a kind of hash tables where each key is present only once in the table, as opposed to the naive usage of the standard Hashtbl module. Its main purpose is to provide efficient implementation of functions such as list_keys with enhanced safety over the direct use of an ('a, 'b list ref) Hashtbl.t type. Many functions have two variants: Example - clustering elements:

Hashtbl2.list_all (Hashtbl2.of_list 10 [ (1, "a"); (2, "b"); (1, "c") ])

returns [(2, ["b"]); (1, ["c"; "a"])].

Hashtbl2 is an additional layer over the standard Hashtbl module.
Author(s): Martin Jambon

type ('a, 'b) t
The type of hash tables from type 'a to type 'b. This representation is suitable for clustering elements according to the given keys.
val create : int -> ('a, 'b) t
Hashtbl2.create n creates a new, empty hash table, with initial size n. For best results, n should be on the order of the expected number of elements that will be in the table. The table grows as needed, so n is just an initial guess.
val clear : ('a, 'b) t -> unit
Empty a hash table.
val add : ('a, 'b) t -> 'a -> 'b -> unit
Hashtbl2.add tbl x y adds a binding of x to y in table tbl. Previous bindings for x are not removed, but simply hidden. That is, after performing Hashtbl2.remove tbl x, the previous binding for x, if any, is restored. (Same behavior as with association lists.)
val copy : ('a, 'b) t -> ('a, 'b) t
Return a copy of the given hashtable.
val find : ('a, 'b) t -> 'a -> 'b
Hashtbl2.find tbl x returns the current binding of x in tbl, or raises Not_found if no such binding exists.
val find_all : ('a, 'b) t -> 'a -> 'b list
Hashtbl2.find_all tbl x returns the list of all data associated with x in tbl. The current binding is returned first, then the previous bindings, in reverse order of introduction in the table.
val mem : ('a, 'b) t -> 'a -> bool
Hashtbl2.mem tbl x checks if x is bound in tbl.
val remove : ('a, 'b) t -> 'a -> unit
Hashtbl2.remove tbl x removes the current binding of x in tbl, restoring the previous binding if it exists. It does nothing if x is not bound in tbl.
val remove_all : ('a, 'b) t -> 'a -> unit
Hashtbl2.remove_all tbl x removes all bindings of x in tbl. It does nothing if x is not bound in tbl.
val replace : ('a, 'b) t -> 'a -> 'b -> unit
Hashtbl2.replace tbl x y replaces the current binding of x in tbl by a binding of x to y. If x is unbound in tbl, a binding of x to y is added to tbl. This is functionally equivalent to Hashtbl2.remove tbl x followed by Hashtbl2.add tbl x y.
val replace_all : ('a, 'b) t -> 'a -> 'b list -> unit
Hashtbl2.replace_all tbl x y replaces all bindings of x in tbl by bindings of x to the elements of y. The first element of y defines the current binding, the second element is the defined the previous binding, and so on.
val iter : ('a -> 'b -> unit) -> ('a, 'b) t -> unit
Hashtbl2.iter f tbl applies f to current bindings in table tbl. f receives the key as first argument, and the associated value as second argument. Each current binding is presented exactly once to f. Hidden bindings are ignored. The order in which the bindings are passed to f is unspecified.
val iter_all : ('a -> 'b list -> unit) -> ('a, 'b) t -> unit
Hashtbl2.iter_all f tbl applies f to all bindings in table tbl. f receives the key as first argument, and all the associated values as second argument in reverse order of introduction in the table. The order in which the bindings are passed to f is unspecified.
val fold : ('a -> 'b -> 'c -> 'c) -> ('a, 'b) t -> 'c -> 'c
Hashtbl2.fold f tbl init computes (f kN dN ... (f k1 d1 init)...), where k1 ... kN are the keys of current bindings in tbl, and d1 ... dN are the associated values. Each current binding is presented exactly once to f. Hidden bindings are ignored.
val fold_all : ('a -> 'b list -> 'c -> 'c) -> ('a, 'b) t -> 'c -> 'c
Hashtbl2.fold_all f tbl init computes (f kN lN ... (f k1 l1 init)...), where k1 ... kN are the keys of all bindings in tbl, and l1 ... lN are the lists of associated values, in reverse order of introduction in the table.
val list_keys : ('a, 'b) t -> 'a list
Hashtbl2.list_keys tbl returns a list of all the keys from the current bindings. Therefore no key is duplicated. Order is unspecified.
val list_values : ('a, 'b) t -> 'b list
Hashtbl2.list_values tbl returns a list of all the values from the current bindings. Hidden bindings are ignored. Order is unspecified.
val list_all_values : ('a, 'b) t -> 'b list list
Hashtbl2.list_all_values tbl returns a list of all the values from all bindings. Order is unspecified.
val list : ('a, 'b) t -> ('a * 'b) list
Hashtbl2.list tbl returns a list of the current bindings. Order is unspecified.
val list_all : ('a, 'b) t -> ('a * 'b list) list
Hashtbl2.list_all tbl returns a list of all the bindings clustered according to their key. Order is unspecified.
val of_list : int -> ('a * 'b) list -> ('a, 'b) t
Hashtbl2.of_list n l converts a list of bindings into a hash table of initial size n. The ordering of the list is the order of introduction of the bindings in the table.
val of_keys : int -> 'a list -> ('a, unit) t
Hashtbl2.of_keys n l converts a list of elements into a hash table of initial size n containing unique copies of these elements bound at most one time to ().