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

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

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

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