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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Negative float problem
Date: 02 Nov 2005 08:32:21 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2005-11-02T08:32:21-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Wed, 02 Nov 2005 10:04:21 +0100, Maciej Sobczak wrote:
> 
> > Dmitry A. Kazakov wrote:
> > 
> >> package A is
> >>    type Foo is ...;
> >>    function "+" (Left, Right : Foo)  return Foo;
> >> end A;
> >> -------------------
> >> package A.B is
> >>    X : Foo;
> >>    function "+" (Left, Right : Foo)  return Foo;
> >> end A.B;
> >> ------------------
> >> with A.B;
> >> ...
> >> A.B.X + A.B.X  -- BOOOOM!
> > 
> > With ADL, I would expect it to call A."+".
> 
> Which perfectly illustrates why there should be no such thing as ADL.
> Exactly to prevent making the above legal with the meaning A."+".

Well, perhaps, but the above example is confusing with the current
rules, too.  If you say "use type A.Foo", you get one "+", when you
might expect to get the other.  Even worse, add this to A.B:
"subtype Foo is A.Foo", and then say "use type A.B.Foo" -- you might be
surprised to get A."+".

I think the answer is a coding convention: If you want to declare an
operator, always make it a primitive of the interesting type involved.
I'm not sure whether that could reasonably be a language rule...

- Bob