Re: Ada2012 : In praise of 'for ... of ... loop'...

[Martin <martin@thedowies.com>]

On Wednesday, May 30, 2012 8:30:21 PM UTC+1, Jeffrey Carter wrote:
> On 05/30/2012 01:10 AM, Martin wrote:
> >
> >        for Comment of Header_Comments loop
> >           Put_Line (File, Comment_Str&  Comment);
> >        end loop;
> >        if Include_Last_Saved_Time then
> >           Put_Line (File, Comment_Str&  "Last saved: "&  Image (Date =>  Clock));
> >        end if;
> >        for Section of This.Sections loop
> >           Put_Line (File, "["&  To_String (Section.Name)&  "]");
> >           for Pair of Section.Pairs loop
> >              Put_Line (File, To_String (Pair.Key)&  "="&  To_String (Pair.Value));
> >           end loop;
> >        end loop;
> 
> This uses 2 inline "for" loops, one containing a nested "for loop".
> 
> >        Close (File);
> >     exception
> >        -- implementation detail
> >     end Save;
> >
> > what we used to have (mocked up!):
> 
> This uses vector iterators.
> 
> While this is a nice feature, I don't think it's worth the added language 
> complexity.
> 
> In general, using "for" loops will be clearer than using iterators. In the case 
> of vectors (or unbounded arrays, to use their correct name), one can iterate 
> over them using "for" loops, and the use of iterators for an array abstraction 
> is a questionable practice:
> 
> for I in Header_Comments.First_Index .. Header_Comments.Last_Index loop
>     Put_Line (File, Comment_Str & Header_Comments.Element (I) );
> end loop;
> 
> if ... then
>     ...
> end if;
> 
> for I in This.Sections.First_Index .. This.Sections.Last_Index loop
>     Section := This.Sections.Element (I);
>     Put_Line ...
> 
>     for J in Section.Pairs.First_Index .. Section.Pairs.Last_Index loop
>        Pair := Section.Pairs.Element (J);
>        Put_Line ...
>     end loop;
> end loop;
> 
> I think this is equally clear and requires no additional language complexity.
> 
> Had your example used sets or maps it would have been a stronger argument.
> 
> -- 
> Jeff Carter
> "He didn't get that nose from playing ping-pong."
> Never Give a Sucker an Even Break
> 110
> 
> --- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

Sorry, I just find that full of "noise" these days...to many characters that are just repeated. and 'Section' and 'Pairs' need to be declared somewhere too. I know you can get rid of the repetition with some 'renames' or a nested subprogram but that's just "noise" and makes more work for the reader.

Aside from the benefits Pascal mentions, the new syntax offers both readability *and writability* which is a bit of a departure for the language ;-)

-- Martin