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Newsgroups: comp.lang.ada
Subject: Re: Rational for not making cursor tagged in Containers
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From: Markus E Leypold
 <development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de>
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Date: Thu, 26 Apr 2007 10:09:20 +0200
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> The predefined equality compares memory bit patterns. 

Without looking into the ARM -- I'd be surprised if the ARM defined it
like this. I'm sure it's more like

  - values numeric types shall be equal if their value are equal
  - array sahll be equal if they are of equal lengths and all components are equal
  - records are equal if all components are equal

Discriminants will complicate this a bit, but the fundamental idea
will stay the same. 

It's up to the implementation to stick to how it -- well -- implements
this semantics. If it compares bit patterns, it will have to pay
attention to uninitialized padding space, but on the other side
comparing bit patterns will probably be very fast. But it _could_ also
just generate loops of sequences of comparisons of the basic
components. As I said: I'm voncinced that's up to the implementation
and I'd suprised if "predefined equality compares memory bit patterns"
as per definition in the ARM.

> Observe, that for any fundamental built-in type there is no way to
> define equality otherwise than this way. An implementation shall
> ensure that different values of the discriminants and the positions
> of values render predefined comparison to false.

Regards -- Markus