[hcoop/debian/mlton.git] / doc / guide / src / MLtonWeak.adoc

MLtonWeak
=========

[source,sml]
----
signature MLTON_WEAK =
   sig
      type 'a t

      val get: 'a t -> 'a option
      val new: 'a -> 'a t
   end
----

A weak pointer is a pointer to an object that is nulled if the object
becomes <:Reachability:unreachable> due to garbage collection.  The
weak pointer does not itself cause the object it points to be retained
by the garbage collector -- only other strong pointers can do that.
For objects that are not allocated in the heap, like integers, a weak
pointer will always be nulled.  So, if `w: int Weak.t`, then
`Weak.get w = NONE`.

* `type 'a t`
+
the type of weak pointers to objects of type `'a`

* `get w`
+
returns `NONE` if the object pointed to by `w` no longer exists.
Otherwise, returns `SOME` of the object pointed to by `w`.

* `new x`
+
returns a weak pointer to `x`.
Commit	Line	Data
7f918cf1 CE	1	MLtonWeak
	2	=========
	3
	4	[source,sml]
	5	----
	6	signature MLTON_WEAK =
	7	sig
	8	type 'a t
	9
	10	val get: 'a t -> 'a option
	11	val new: 'a -> 'a t
	12	end
	13	----
	14
	15	A weak pointer is a pointer to an object that is nulled if the object
	16	becomes <:Reachability:unreachable> due to garbage collection. The
	17	weak pointer does not itself cause the object it points to be retained
	18	by the garbage collector -- only other strong pointers can do that.
	19	For objects that are not allocated in the heap, like integers, a weak
	20	pointer will always be nulled. So, if `w: int Weak.t`, then
	21	`Weak.get w = NONE`.
	22
	23	* `type 'a t`
	24	+
	25	the type of weak pointers to objects of type `'a`
	26
	27	* `get w`
	28	+
	29	returns `NONE` if the object pointed to by `w` no longer exists.
	30	Otherwise, returns `SOME` of the object pointed to by `w`.
	31
	32	* `new x`
	33	+
	34	returns a weak pointer to `x`.