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Weak(3) 				  OCaml library 				  Weak(3)

NAME
       Weak - Arrays of weak pointers and hash tables of weak pointers.

Module
       Module	Weak

Documentation
       Module Weak
	: sig end

       Arrays of weak pointers and hash tables of weak pointers.

       === Low-level functions ===

       type 'a t

       The  type  of  arrays  of weak pointers (weak arrays).  A weak pointer is a value that the
       garbage collector may erase whenever the value is not used any more (through normal point-
       ers) by the program.  Note that finalisation functions are run after the weak pointers are
       erased.

       A weak pointer is said to be full if it points to a value, empty if the value  was  erased
       by the GC.

       Notes:

       -Integers are not allocated and cannot be stored in weak arrays.

       -Weak  arrays  cannot  be marshaled using Pervasives.output_value nor the functions of the
       Marshal module.

       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 .

       === Weak hash tables ===

       === A weak hash table is a hashed set of values. Each value may magically  disappear  from
       the  set when it is not used by the rest of the program any more. This is normally used to
       share data structures without inducing memory leaks.  Weak hash tables are defined on val-
       ues  from a Hashtbl.HashedType module; the equal relation and hash function are taken from
       that module. We will say that v is an instance of x if equal x v is true.  The equal rela-
       tion must be able to work on a shallow copy of the values and give the same result as with
       the values themselves. ===

       module type S = sig end

       The output signature of the functor Weak.Make .

       module Make : functor (H : Hashtbl.HashedType) -> sig end

       Functor building an implementation of the weak hash table structure.

OCamldoc				    2014-06-09					  Weak(3)
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