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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Grace and Maps (was Re: Development process in the Ada community)
Date: Wed, 24 Apr 2002 14:14:34 -0500
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Date: 2002-04-24T14:14:34-05:00
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Ole-Hjalmar Kristensen wrote in message
<7vbsc9w367.fsf@vlinux.voxelvision.no>...
>Darren New <dnew@san.rr.com> writes:

>> how to do this in Ada, tho - it would seem that every private type
>> (for example) would have to implement its own hash
>> function. Wouldn't it?
>
>Hmm. What's wrong with having a generic hash function which you
>instantiate for your private type? Provided that you can read the key
>as an array of bytes, it should work the same in both C and Ada. I
>know this is low-level and dirty, but for hashing, I think it's a
>reasonable approach.


Actually, it doesn't even need to be generic. It is easy to write a
hashing algorithm that works with any type that can be streamed (use
streaming operations to convert to an array of stream elements, hash
that) -- I've seen two such implementations in the last few days.

Using streams to do this has the advantage of eliminating packing and
implementation-defined components from concern. It does limit the
applicability of the package to non-limited keys, but that seems to be
an acceptable limitation (do you really need to hash tasks??).

              Randy.