Re: hash tables and GC

[smh@EMS.MEDIA.MIT.EDU (Steven Haflich)]

   From: David L. Andre <DLA@JASPER.SCRC.Symbolics.COM>
   Subject: Re:  hash tables and GC
   
       0. Can such tables be implemented?
   
   Proof by existence:  We have had such tables prototyped internally at
   Symbolics for a year or so, but have not had the resources to qualify
   them for release to customers.  They can be quite efficient, and of
   course can significantly improve the efficiency of some kinds of
   programs.

But perhaps this isn't exactly the right question for such a late date
in the CL standards process.  Rather:

   Can such tables be implemented with reasonable performance
   in *all* existing CL implementations, without breaking the GC
   strategies upon which they depend?

I myself have no idea which way this question would fall, but unless
it could confidently be answered in the affirmative I feel X3J13 would
have to exclude these `weak-pointer' tables from the standard.  The
*real* problem is that it would be incumbent on the *proposer* to
prove practicality.  This would not be an easy proof.