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From: ica2ph@alpha1.csv.ica.uni-stuttgart.de (Peter Hermann)
Subject: Re: Uninitialized "out" parameters
Date: 1996/07/23
Message-ID: <4t20tb$1bum@info4.rus.uni-stuttgart.de>#1/1
X-Deja-AN: 169666037
references: <4som64$775@newsbf02.news.aol.com>
 <Dut6tq.GCD.0.-s@inmet.camb.inmet.com>
organization: Comp.Center (RUS), U of Stuttgart, FRG
newsgroups: comp.lang.ada
Date: 1996-07-23T00:00:00+00:00
List-Id: <comp.lang.ada>


Tucker Taft (stt@henning.camb.inmet.com) wrote:
: It is hard to know which error is more common, the Ada 83
: one where you create a local read/write variable and then forget to 
: assign it on all exit paths to the OUT parameter, or the Ada 95
: one where you forget to initialize the read/write OUT parameter.

: Having experienced the Ada 83 situation for 10 years, I remember
: having made the Ada 83 error several times.  It is too early to tell

me too ... and then quickly changing to John Herro's solution.
(while grumbling ;-)

: how it will compare in frequency to the Ada 95 error.

: The main advantage is that it simplifies the language, since
: you only have one rule -- initialize your variables -- rather than
: two.  Ada 83's unreadable OUT parameters require a special
: paradigm, and introduce a second class of errors, when you need
: to build up an answer incrementally.

For the Ada83 class of errors I ask you for an example.

I consider the current Ada95 rule a true source of errors
and therefore a nasty property of the language.
I could imagine an Ada2005 where the compiler is obliged to only
allow any downstream reading of mode-"OUT"-parameters 
when the context clearly indicates a prior setting,
whatever flow of control was taken before.

BTW, under NO circumstances I would accept an incoming value of 
a formal OUT parameter as data to be processed. I am sure you all agree.

I am not satisfied with the language concerning
the handling of non-initialized variables in general.
This has been discussed long time ago. 
I remember e.g. the efficiency aspect.

--
Peter Hermann  Tel:+49-711-685-3611 Fax:3758 ph@csv.ica.uni-stuttgart.de
Pfaffenwaldring 27, 70569 Stuttgart Uni Computeranwendungen
Team Ada: "C'mon people let the world begin" (Paul McCartney)