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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Operation can be dispatching in only one type
Newsgroups: comp.lang.ada
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Date: Tue, 1 Dec 2009 14:48:31 +0100
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Date: 2009-12-01T14:48:31+01:00
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On Tue, 01 Dec 2009 13:13:29 +0100, Georg Bauhaus wrote:

> Then we could rely on the language: compilers will detect
> uninitialized variables provided these do not have a pragma/keyword/...
> to say that uninitialized is what the programmer wants.
> Some fancy means to tell the compiler that this variable
> does indeed have a good first value like pragma Import.
> 
>    X : [constant] Car; -- default init,

The error is here!
>                        -- undefined,
>                        -- junk bits. Doesn't matter
>    --  *no* pragma Import (Ada, X);
> 
> begin
> 
>    Spare := X.Tire (5); -- would become illegal,

Not here!

-------------------------
Anyway, you cannot do that because:

   if HALT (P) then
     X := Z;
   end if;
   Y := X;  -- Is this legal?

> Does the phrase "first value" make sense?

An object shall not have invalid values. All values are valid if the
language is typed. Enforcing user-defined construction including
prohibition of certain kinds of construction (e.g. per default constructor)
is a different story.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de