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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Rational for not making cursor tagged in Containers
Date: Fri, 27 Apr 2007 16:44:58 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2007-04-27T16:44:58-04:00
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Markus E Leypold
<development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de> writes:

> "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

That's correct.

There are cases where it can't compare bit patterns.

For floating point, negative zero is equal to positive zero.

For a boolean type with convention Fortran:

    type Logical is new Boolean;
    pragma Convention(Fortran, Logical);

The representation is "zero is false, anything else is true".

User-defined "=" composes properly in the tagged case.

- Bob