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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Uninitialized out parameters.
Date: Wed, 6 Apr 2016 16:03:34 -0500
Organization: JSA Research & Innovation
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<Stefan.Lucks@uni-weimar.de> wrote in message 
news:alpine.DEB.2.20.1604062240350.29458@debian...
On Wed, 6 Apr 2016, ahlan@marriott.org wrote:

> In the annotated RM, in the section concerning Null Procedures, it says
> "There are no null functions because the return value has to be
> constructed somehow; a function that always raises Program_Error doesn't
> seem very useful or worth the complication" If there are no null
> functions because a return value has to be constructed then surely the
> same applies to null procedures that have out parameters. These too
> should be prohibited [...]

This seems to be right. It does not make much sense to allow the
declaration of

  procedure X(Formal: out T) is null;

while prohibiting the declaration of

  function Y return R is null;

The point is, you can neither call X nor Y. Semantically, both statements

  X(Actual);
  Actual := Y;

are equally useless, or at least their effect is equally undefined.
Allowing the declaration of X, but prohibiting the declaration of Y is
inconsistent.


If people really think they need to declare something like the above
procedure X, a revised Ada standard could allow declarations such as

  procedure X(Formal: T) is raise;

and

  function Y return T is raise;

where "is raise" stands for "raise Program_Error". That may sometimes come
handy in the context of inheritance, or so.


--------  I  love  the  taste  of  Cryptanalysis  in  the morning!  --------
www.uni-weimar.de/de/medien/professuren/mediensicherheit/people/stefan-lucks
----Stefan.Lucks (at) uni-weimar.de, Bauhaus-Universität Weimar, Germany----