Re: How to make like Fortran "do i = 1,20,2"

[Gary Scott <Gary.L.Scott@lmtas.lmco.com>]

You can also design this same abstraction in Fortran if you like and for
something like initialization of a whole array or section, it could be
reduced to a single statement.

des walker wrote:
> 
> Reinert Korsnes wrote:
> 
> > Hi,
> >
> > How can one in Ada elegantly make a loop through each 2 element of an array ?
> > I am looking for something like: "do i = 1,20,2" in Fortran, or
> >
> > for I in A'range ("step 2") loop
> >    something...
> > end loop;
> >
> > Yes, I can use:
> >
> > I := A'first;
> > while I <= A'Last loop;
> >   something..
> >   I := I + 2;
> > end loop;
> >
> > But this does not look so elegant....
> >
> > reinert
> >
> > --
> > Norwegian Polar Institute
> > Polar Environment Center
> > N-9296 Tromso
> > Norway
> > Fax: +47 77750501
> >
> > http://geophys.npolar.no/~reinert/personal.html
> 
> Often wanting to process data in this manner would suggest that there might be a
> more meaningful way to express the structure of the data. A lot of effort can be
> spent in Ada designing good data types which makes it simple to write safe code.
> 
> If the two element blocks of your array hold, say, a coordinate pair you might
> have
> 
> type coordinate is record
>   X,Y : integer;
> end record;
> 
> type coordinate_array is array(Natural range <>) of coordinate;
> 
> then processing the array reduces to
> 
> procedure Process_Array(The_Array : in coordinate_array) is
> begin
>   for I in The_Array'first .. The_Array'last loop
>     Do_Something(The_Array(I));
>   end loop;
> end Process_Array;
> 
> Now the elegance is returned to the loop block.
> An earlier respondent also mentioned that there is no guarantee that your
> original array is an even number of elements long, here the problem is neatly
> avoided because the array will consist of complete elements.
> 
> I realise that it is not always possible to backtrack on data structures that are
> already defined, but Data Abstraction in Ada is a good tool for writing safe,
> extensible code.
> 
>     Des
>     Alenia-Marconi Systems