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From: Dmitry A.Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Concatenation and Characters
Date: Sun, 20 Oct 2002 04:01:13 +0200
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Date: 2002-10-20T04:01:13+02:00
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Mark Biggar wrote:

> Programmer Dude wrote:

>> I'm new to, and just beginning to explore, Ada.  It surprised me that
>> Ada allows evalutation of an uninitialized variable without saying
>> *something* about it during compile.
>> 
>> Surely I'm missing something?
> 
> It should be obvious that the general problem of detecting all
> accesses to uninitialized variables is equivalent to the halting
> problem.  So it is impossible for a compiler to do a perfect job, thus
> some form of run-time detection or action is necessary anyway.  So the
> LRM can't require compile time detection, so it makes it optional.  The
> LRM does allow compilers to warn you when you write code that will
> always raise an expection and as raising Program_Error is one of the
> allowed run-time responses to accessing an uninitialized variable the
> LRM does allows for optional warnings for this case.  If your complier
> doesn't issue such warnings, it's only a "quality of implementation"
> issue not a compiler bug.

I think you missed the point. The question was about the language not a 
compiler.

It is true that no compiler can detect all uninitialized variables. So?

Then the language shall require them to be either initialized or 
*explicitly* specified as uninitialized:

X : Integer with null; -- or some other syntax

Maybe one should require this also for out-parameters (via default value):

procedure Foo (X : out Integer := 23);
function Foo returns Integer := 23;

-- 
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de