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From: "Randy Brukardt" <randy@rrsoftware.com>
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Subject: Re: Hashing on System.Address
Date: Tue, 14 Jun 2005 15:03:23 -0500
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Date: 2005-06-14T15:03:23-05:00
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"Duncan Sands" <baldrick@free.fr> wrote in message
news:mailman.25.1118740226.17633.comp.lang.ada@ada-france.org...
> > > By the way, is there any reason why Ada.Containers doesn't provide
some
> > > standard hash functions?  I reckon hashing on strings and on addresses
> > > would be pretty handy.
> >
> > Out of Containers hierarchy: Ada.Strings.Hash
>
> You know, this implementation advice sounds pretty silly:
>
> Implementation Advice
> 7/2
>      The various Hash functions should be good hash functions, returning a
wide spread of values for different string values. It should be unlikely for
similar strings to return the same value.
>
> As if any implementor needs to be told that they should use a "good"
rather than a "bad"
> hash function!

We'd have preferred to say something stronger, and normatively, but there
doesn't seem to be a way to describe what a hash function does, other than
returning a value of Hash_Type that depends of the argument. So we use IA to
describe what the intent is; IA can be informal and use undefined terms like
"good".

Without the IA, the only indication that this is a hash function is the
name. That wouldn't be enough. And if you don't know what a hash function
is, the IA will be helpful.

                                    Randy.