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(*                                                                     *)
(*                           Objective Caml                            *)
(*                                                                     *)
(*            Damien Doligez, projet Para, INRIA Rocquencourt          *)
(*                                                                     *)
(*  Copyright 1997 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.     *)
(*                                                                     *)
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(* $Id$ *)

(** Arrays of weak pointers. *)

type 'a t
(** The type of arrays of weak pointers (weak arrays).  A weak
   pointer is a value that the garbage collector may erase at
   any time.
   A weak pointer is said to be full if it points to a value,
   empty if the value was erased by the GC.*)


val create : int -> 'a t
(** [Weak.create n] returns a new weak array of length [n].
   All the pointers are initially empty.  Raise [Invalid_argument]
   if [n] is negative or greater than {!Sys.max_array_length}[-1].*)

val length : 'a t -> int
(** [Weak.length ar] returns the length (number of elements) of
   [ar].*)

val set : 'a t -> int -> 'a option -> unit
(** [Weak.set ar n (Some el)] sets the [n]th cell of [ar] to be a
   (full) pointer to [el]; [Weak.set ar n None] sets the [n]th
   cell of [ar] to empty.
   Raise [Invalid_argument "Weak.set"] if [n] is not in the range
   0 to {!Weak.length}[ a - 1].*)

val get : 'a t -> int -> 'a option
(** [Weak.get ar n] returns None if the [n]th cell of [ar] is
   empty, [Some x] (where [x] is the value) if it is full.
   Raise [Invalid_argument "Weak.get"] if [n] is not in the range
   0 to {!Weak.length}[ a - 1].*)

val get_copy : 'a t -> int -> 'a option
(** [Weak.get_copy ar n] returns None if the [n]th cell of [ar] is
   empty, [Some x] (where [x] is a (shallow) copy of the value) if
   it is full.
   In addition to pitfalls with mutable values, the interesting
   difference with [get] is that [get_copy] does not prevent
   the incremental GC from erasing the value in its current cycle
   ([get] may delay the erasure to the next GC cycle).
   Raise [Invalid_argument "Weak.get"] if [n] is not in the range
   0 to {!Weak.length}[ a - 1].*)


val check : 'a t -> int -> bool
(** [Weak.check ar n] returns [true] if the [n]th cell of [ar] is
   full, [false] if it is empty.  Note that even if [Weak.check ar n]
   returns [true], a subsequent {!Weak.get}[ ar n] can return [None].*)

val fill : 'a t -> int -> int -> 'a option -> unit
(** [Weak.fill ar ofs len el] sets to [el] all pointers of [ar] from
   [ofs] to [ofs + len - 1].  Raise [Invalid_argument "Weak.fill"]
   if [ofs] and [len] do not designate a valid subarray of [a].*)

val blit : 'a t -> int -> 'a t -> int -> int -> unit
(** [Weak.blit ar1 off1 ar2 off2 len] copies [len] weak pointers
   from [ar1] (starting at [off1]) to [ar2] (starting at [off2]).
   It works correctly even if [ar1] and [ar2] are the same.
   Raise [Invalid_argument "Weak.blit"] if [off1] and [len] do
   not designate a valid subarray of [ar1], or if [off2] and [len]
   do not designate a valid subarray of [ar2].*)