Re: Ada2012 : Expression functions and extended return statements

[stefan-lucks@see-the.signature]

On Fri, 6 Jan 2012, Martin wrote:

> On Jan 6, 9:45�am, stefan-lu...@see-the.signature wrote:
> > On Fri, 6 Jan 2012, Martin wrote:
> > > Also, on the topic of extended return statements...
> >
> > > What's the rational for having to explicitly repeat the return type?
> > > Seems rather redundant to my eyes. I wouldn't have minded:
> >
> > I guess, this is because the object actually returned may not necessarily
> > be of exactly the same type of subtype as the declared return type -- like
> > the ordinary return statement. See the following examples:
> >
> > � �function Characters(I: Integer; Filler: Character := '_') return String is
> > � �begin
> > � � � return Result: String(1..I) := (others => Filler) do
> > � � � � return;
>           ^^^^^^^
> 
> I think you mean
>         null;
> or
>         return Result: String(1..I) := (others => Filler);

The following compiles fine (with gnat 2011), and the output is xxxyyx, as 
to be expected:

<lang Ada>

with Ada.Text_IO;

procedure Y is

   function Characters(I: Integer; Filler: Character := '_') return String is
   begin
      return Result: String(1..I) := (others => Filler) do
        return;
      end return;
   end Characters;

begin
   Ada.Text_IO.Put(Characters(3, 'x'));
   Ada.Text_IO.Put(Characters(2, 'y'));
   Ada.Text_IO.Put(Characters(1, 'x'));
   Ada.Text_IO.Put(Characters(0, 'y'));
end Y;

</lang>

> 
> > � � � end return;
> > � �end Characters;
> >
> > � �type T is tagged record I: Integer; end record;
> > � �type S is new T with record J: Natural; end record;
> >
> > � �function Fun(N, M: Natural) return T'Class is
> > � �begin
> > � � � return Result: S do
> > � � � � Result.I := M;
> > � � � � Result.J := N;
> > � � � end return;
> > � �end Fun;
> >
> > --
> > ---- Stefan.Lucks (at) uni-weimar.de, University of Weimar, Germany �----
> > � � <http://www.uni-weimar.de/cms/medien/mediensicherheit/home.html>
> > ------ �I �love �the �taste �of �Cryptanalysis �in �the �morning! �------
> 
> 
> Ah ok, yes, that makes sense...thanks. Never had need of
> this...yet! :-)
> 
> I still think it would be nice to have a short-hand e.g. 'return
> Result : <> do'. If anything it would then draw the eye to the more
> interesting case when the 2 are different.
> 
> -- Martin
> 

-- 
---- Stefan.Lucks (at) uni-weimar.de, University of Weimar, Germany  ----
    <http://www.uni-weimar.de/cms/medien/mediensicherheit/home.html>
------  I  love  the  taste  of  Cryptanalysis  in  the  morning!  ------