basis-library/mlton/weak.sml

   1 (* Copyright (C) 2003-2006 Henry Cejtin, Matthew Fluet, Suresh
   2  *    Jagannathan, and Stephen Weeks.
   3  *
   4  * MLton is released under a BSD-style license.
   5  * See the file MLton-LICENSE for details.
   6  *)
   7
   8 structure MLtonWeak =
   9    struct
  10       structure Weak = Primitive.MLton.Weak
  11
  12       type 'a t = 'a Weak.t
  13
  14       val new = Weak.new
  15
  16       fun get (w: 'a t): 'a option =
  17          let
  18             (* Need to do the canGet after the get.  If you did the canGet first,
  19              * there could be a GC that invalidates the pointer between the
  20              * canGet and the get.
  21              *)
  22             val x = Weak.get w
  23          in
  24             if Weak.canGet w
  25                then SOME x
  26             else NONE
  27          end
  28    end