Re: [Caml-list] Clarification for the configuration of comparison functions

[Gerd Stolpmann <info@gerd-stolpmann.de>]

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Am Mittwoch, den 10.09.2014, 08:40 -0400 schrieb Nick Lucaroni
> On Sep 10, 2014 8:27 AM, "Gerd Stolpmann" <info@gerd-stolpmann.de>
> wrote:
> > There is something else that can speed up a custom compare: you can
> also
> > store a hash of the value inside the value, and use that for
> speeding up
> > comparison, e.g.
> >
> > type t = ...
> > type t_cmp = t * int
> >
> > let wrap x = (x, Hashtbl.hash x)
> >
> > let my_compare (x1,h1) (x2,h2) =
> >   if h1=h2 then
> >     compare x1 x2
> >   else
> >     h1-h2
> 
> The hash difference here would cause issues, is it really worth it if
> you have to recover some ordering anyway? I can see the value in
> defining equality, though.

For example, if you need the ordering only for a Map or Set, it doesn't
matter how things are ordered.

Gerd
-- 
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Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
My OCaml site:          http://www.camlcity.org
Contact details:        http://www.camlcity.org/contact.html
Company homepage:       http://www.gerd-stolpmann.de
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