From: Xavier Leroy <Xavier.Leroy@inria.fr>
To: Thomas Fischbacher <Thomas.Fischbacher@Physik.Uni-Muenchen.DE>
Cc: Christian Lindig <lindig@cs.uni-sb.de>, Caml List <caml-list@inria.fr>
Subject: Re: [Caml-list] EQ hash tables?
Date: Wed, 12 Oct 2005 10:02:48 +0200 [thread overview]
Message-ID: <434CC328.7060803@inria.fr> (raw)
In-Reply-To: <Pine.LNX.4.61.0510111652370.10250@katrin.cip.physik.uni-muenchen.de>
> Actually, this brings me to a question I wanted to ask for a long time:
> while I never used this so far, I just assumed that OCaml does provide
> hash tables where keys are compared w.r.t. "being the same" ('==' , that
> is), rather than only hash tables where keys are compared for "being
> equal" (say, '=').
Easily definable using the functorial interface to hash tables:
module MyEqHashTable =
Hashtbl.Make(struct
type t = my_type_for_keys
let equal = (==)
let hash = Hashtbl.hash
end)
> Of course, "EQ hash tables" have to be treated in a slightly special way
> when talking about stop© GCing.
No, not "of course". You're thinking of using the address of a memory
block as its hash value. This indeed requires GC support. But you
can get the semantics you want (keys compared by reference) while
still computing the hash code structurally. This is what the code
snippet above does.
- Xavier Leroy
next prev parent reply other threads:[~2005-10-12 8:02 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-10 13:42 [Caml-list] possible to define a type where = is forbidden ? yoann padioleau
2005-10-10 15:04 ` Thomas Fischbacher
2005-10-11 14:56 ` EQ hash tables? Thomas Fischbacher
2005-10-12 7:41 ` [Caml-list] " Hendrik Tews
2005-10-12 8:02 ` Xavier Leroy [this message]
2005-10-12 11:11 ` Thomas Fischbacher
2005-10-12 15:06 ` Xavier Leroy
2005-10-12 17:53 ` Thomas Fischbacher
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