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From: Maciej Sobczak <no.spam@no.spam.com>
Newsgroups: comp.lang.ada
Subject: Re: Negative float problem
Date: Wed, 02 Nov 2005 10:04:21 +0100
Organization: CERN - European Laboratory for Particle Physics
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Xref: g2news1.google.com comp.lang.ada:6110
Date: 2005-11-02T10:04:21+01:00
List-Id: <comp.lang.ada>

Dmitry A. Kazakov wrote:

> package A is
>    type Foo is ...;
> 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  -- Why this does not work?

Because "+" is not directly visible.

ADL would not help here, because A.B.X is of type Foo, which is defined 
in A, and there is no "+" defined in this package.


> And now consider this:
> 
> 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!

Why BOOOOM? It still doesn't work, for the same reason.

With ADL, I would expect it to call A."+". This means that some program, 
which is not legal without ADL, would be legal with ADL in the language.

(If your point is that any language feature can seem obscure when shown 
in obscure examples, then I completely agree.)


-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/