Comment author: administrator

On Friday, March 7, 2003, at 12:13 AM, alex@baretta.com wrote:

I'm not sure whether this is a bug or a feature.

I need to save the state of the Xcaml session between CGI
executions. Thinking in terms of Jserv-compliant
implementation, i used a Weak.Make(...).t hashtable to store
session data, so that old and no longer used data might be
automatically reclaimed by the GC. However, I found that
this implementation is buggy, because when I marshal and
unmarshal the weak hashtable, I always get an empty
hashtable back. Why is this?

I'm not sure I understand what you are doing. Are you
marshalling the weak hash table by itself, or as part of a
bigger data structure ?

One more remark concerning the Weak.Make functor. Why in the
world are Hashtbl.Make and Weak.Make incompatible?

Weak hash tables were originally designed for hash-consing.
In this context, it doesn't make much sense to have key-value
pairs in the hash table: the hash table must be self-keyed.
Moreover, self-keyed weak hash tables are more efficient and
easier to implement. Also, the binding-order properties of
normal hash tables would not be satisfied by weak hash tables.

It is
only natural to think of the second as a particularly clever
implementation of the first. Besides, the two modules are so
similar that really deserve to have the same signatures. I
strongly encourage the Caml Masters to think this over.

If anything, we should change the Hashtbl.Make hash tables
to be self-keyed too. But that would in turn complicate the
interface of the generic hash tables...

Of
course, I could reimplement the Weak.Make functor in a Weak2
module for the ocamllib-addons package, but is it worth it?

I think there are already several implementations of key-value
weak hash tables out there...

-- Damien