From: ts <decoux@...>
Date: 2003-12-09T19:17:39+09:00
Subject: Re: WeakRef and Object#hash

>>>>> "R" == Robert Klemme <bob.news@gmx.net> writes:

R> What can we do about this in Ruby if we want the instance to be GC'ed?  Is
R> there a workaround at least for testing purposes?

 Like has said matz, nothing.

 But there is something worst, be carefull with weakref : the example was
 given in ruby-core. Someone created weakrefs and stored the ID of the
 reference in a hash and when he wanted to retrieve the object he called
 _id2ref. His algorithm was :
   * _id2ref raise an error ==> this mean that the object was recycled
   * otherwise it retrieve the original object.


 Except that one day he has a big surprise, because ruby has recycled one
 his object and *re-use* the same reference for one of its internal
 object. When he  called _id2ref, ruby has returned the internal object
 and it dont really liked to find it, latter, in a ruby variable.

 This is why _id2ref was modified (i.e. it can't return internal object) to
 protect ruby if someone else use this wrong algorithm. Because the
 algorithm is still wrong.

 Just imagine :
   * you create a weakref from an Array and store the ID
   * ruby recycle the Array and re-use the same reference for an Hash
   * you call _id2ref, ruby return the new Hash and not the original Array 


Guy Decoux