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Date: Thu, 10 Apr 2014 10:42:17 +0200
From: Georg Bauhaus <rm-host.bauhaus@maps.futureapps.de>
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Newsgroups: comp.lang.ada
Subject: Re: Your wish list for Ada 202X
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Date: 2014-04-10T10:42:17+02:00
List-Id: <comp.lang.ada>

On 10/04/14 05:28, Randy Brukardt wrote:
>>> But it's all we have. Sure, you can map a tag (this requires a loop,
>>> >>either
>>> >>a brute force lookup or some fancier but much more code-intensive
>>> >>version),
>>> >>but that's going to make dispatching far more expensive. You can't do
>>> >>this
>>> >>mapping at compile-time because what mapping you need depends on the
>>> >>interfaces in use.
>> >
>> >I can build a perfect hash at bind/link time when all involved tags become
>> >known.
> "can" means "possible", not "practical". That might be possible if the
> number of tags is small, but that's not the case in a lot of OO systems. (A
> Claw program starts with somewhere around 80.) Finding a perfect hash gets
> very time consuming if the number of items is large - I don't think people
> will be very happy with binding that takes 12 hours.

Are you certain about the cost of computing perfect hashes?
I tried gperf(1) on a hundred words and ran it a thousand times
in a loop. The loop has taken just a few seconds:

a=1000
while test $a -gt 0
  do
     head -100 /usr/share/dict/words |gperf > /dev/null
    a=$(($a - 1))
  done