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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada2012 : Expression functions and extended return statements
Date: Fri, 6 Jan 2012 18:20:12 +0100
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Date: 2012-01-06T18:20:12+01:00
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On Fri, 06 Jan 2012 08:45:22 -0600, Martin Dowie wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote:

>> This is not a declaration, because the result is not an object.
> 
> 2012 RM 3.1 6/3 says it is a declaration (but I should have written
> 'Result' not 'Return').

Surely it says so, but it is not a declaration of the result object.

When the result is copy-out, it is another object which value could become
the value of the result object proper.

Even for limited types it is still not necessarily the result object. In
fact it is undecidable to figure out if it is:

   return X : Limited_T do
      if Halt (p) then
         raise I_Want_It_Otherwise;
      end if;
      ...
   end return;
exception
   when I_Want_It_Otherwise =>
      return Y : Limited_T do
          ...
      end return;

Who is the result object, X or Y?

The problem is that it is inherently inconsistent to have result objects
declared within the function body. What Ada actually does is no different
from a local variable, because there is no other way to return anything
from a subprogram. Why bother introducing awful syntax, which does not mean
what it is supposed to do?

> The evolution of Ada has always resulted in adding things that aren't
> "Ada-like" when compared to the previous revision.

Alas. Return statement is certainly not.

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