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(***********************************************************************)
(* *)
(* Objective Caml *)
(* *)
(* Xavier Leroy, projet Cristal, INRIA Rocquencourt *)
(* *)
(* Copyright 1996 Institut National de Recherche en Informatique et *)
(* en Automatique. All rights reserved. This file is distributed *)
(* under the terms of the GNU Library General Public License, with *)
(* the special exception on linking described in file ../LICENSE. *)
(* *)
(***********************************************************************)
(* $Id$ *)
(** Hash tables and hash functions.
Hash tables are hashed association tables, with in-place modification.
*)
(** {6 Generic interface} *)
type ('a, 'b) t
(** The type of hash tables from type ['a] to type ['b]. *)
val create : int -> ('a, 'b) t
(** [Hashtbl.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
(** [Hashtbl.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 {!Hashtbl.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
(** [Hashtbl.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
(** [Hashtbl.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
(** [Hashtbl.mem tbl x] checks if [x] is bound in [tbl]. *)
val remove : ('a, 'b) t -> 'a -> unit
(** [Hashtbl.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 replace : ('a, 'b) t -> 'a -> 'b -> unit
(** [Hashtbl.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 {!Hashtbl.remove}[ tbl x]
followed by {!Hashtbl.add}[ tbl x y]. *)
val iter : ('a -> 'b -> unit) -> ('a, 'b) t -> unit
(** [Hashtbl.iter f tbl] applies [f] to all bindings in table [tbl].
[f] receives the key as first argument, and the associated value
as second argument. Each binding is presented exactly once to [f].
The order in which the bindings are passed to [f] is unspecified.
However, if the table contains several bindings for the same key,
they are passed to [f] in reverse order of introduction, that is,
the most recent binding is passed first. *)
val fold : ('a -> 'b -> 'c -> 'c) -> ('a, 'b) t -> 'c -> 'c
(** [Hashtbl.fold f tbl init] computes
[(f kN dN ... (f k1 d1 init)...)],
where [k1 ... kN] are the keys of all bindings in [tbl],
and [d1 ... dN] are the associated values.
Each binding is presented exactly once to [f].
The order in which the bindings are passed to [f] is unspecified.
However, if the table contains several bindings for the same key,
they are passed to [f] in reverse order of introduction, that is,
the most recent binding is passed first. *)
(** {6 Functorial interface} *)
module type HashedType =
sig
type t
(** The type of the hashtable keys. *)
val equal : t -> t -> bool
(** The equality predicate used to compare keys. *)
val hash : t -> int
(** A hashing function on keys. It must be such that if two keys are
equal according to [equal], then they have identical hash values
as computed by [hash].
Examples: suitable ([equal], [hash]) pairs for arbitrary key
types include
([(=)], {!Hashtbl.hash}) for comparing objects by structure, and
([(==)], {!Hashtbl.hash}) for comparing objects by addresses
(e.g. for mutable or cyclic keys). *)
end
(** The input signature of the functor {!Hashtbl.Make}. *)
module type S =
sig
type key
type 'a t
val create : int -> 'a t
val clear : 'a t -> unit
val copy : 'a t -> 'a t
val add : 'a t -> key -> 'a -> unit
val remove : 'a t -> key -> unit
val find : 'a t -> key -> 'a
val find_all : 'a t -> key -> 'a list
val replace : 'a t -> key -> 'a -> unit
val mem : 'a t -> key -> bool
val iter : (key -> 'a -> unit) -> 'a t -> unit
val fold : (key -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b
end
(** The output signature of the functor {!Hashtbl.Make}. *)
module Make (H : HashedType) : S with type key = H.t
(** Functor building an implementation of the hashtable structure.
The functor [Hashtbl.Make] returns a structure containing
a type [key] of keys and a type ['a t] of hash tables
associating data of type ['a] to keys of type [key].
The operations perform similarly to those of the generic
interface, but use the hashing and equality functions
specified in the functor argument [H] instead of generic
equality and hashing. *)
(** {6 The polymorphic hash primitive} *)
val hash : 'a -> int
(** [Hashtbl.hash x] associates a positive integer to any value of
any type. It is guaranteed that
if [x = y], then [hash x = hash y].
Moreover, [hash] always terminates, even on cyclic
structures. *)
external hash_param : int -> int -> 'a -> int = "hash_univ_param" "noalloc"
(** [Hashtbl.hash_param n m x] computes a hash value for [x], with the
same properties as for [hash]. The two extra parameters [n] and
[m] give more precise control over hashing. Hashing performs a
depth-first, right-to-left traversal of the structure [x], stopping
after [n] meaningful nodes were encountered, or [m] nodes,
meaningful or not, were encountered. Meaningful nodes are: integers;
floating-point numbers; strings; characters; booleans; and constant
constructors. Larger values of [m] and [n] means that more
nodes are taken into account to compute the final hash
value, and therefore collisions are less likely to happen.
However, hashing takes longer. The parameters [m] and [n]
govern the tradeoff between accuracy and speed. *)
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