Re: [Chicken-janitors] #1293: eq?-hash tables calculcate different value for objects after they're mutated and lose locatives after GC

[Chicken Trac]

#1293: eq?-hash tables calculcate different value for objects after they're
mutated and lose locatives after GC
-----------------------------+---------------------------------------------
  Reporter:  sjamaan         |      Owner:
      Type:  defect          |     Status:  new
  Priority:  critical        |  Milestone:  4.12.0
 Component:  core libraries  |    Version:  4.10.x
Resolution:                  |   Keywords:  srfi-69, hash tables, locatives
-----------------------------+---------------------------------------------

Comment (by sjamaan):

 One (very) ugly way to "fix" this is to change `hash-by-identity`: It can
 simply hash the object's pointer, and record it in a side table along with
 the current pointer.  This means that every object that ever was hashed
 has an entry in that table.

 Whenever the object is moved, update the current pointer.  Then, if the
 object is looked up again we can obtain the originally assigned hash
 value.  On major GC, walk the table and remove all the keys that no longer
 exist.

 It's ugly and stupid and takes up a lot of unnecessary memory.  I really
 don't like it, but we could do this in a generic/reusable way and also use
 it in core's symbol table, for example.

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Ticket URL: <http://bugs.call-cc.org/ticket/1293#comment:7>
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