doc/guide/src/MLtonWeak.adoc

   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`.