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

["Ken Garlington" <Ken.Garlington@computer.org>]

"Reinert Korsnes" <reinert@ola.npolar.no> wrote in message
news:8lpcbe$40n$1@news.uit.no...
>
> 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....

Just off the top of my head:

for I in Beginning_Selection .. Final_Selection loop

   something involving A(Selected_By(I));

end loop;

where the functions come from a generic with a Step constant and an array
index type as parameters, with functions sketched as

  Beginning_Selection: Type'First;
  Final_Selection: Type'First + (Type'Length/Step) - 1 -- depends upon what
you want to do with odd-valued arrays, etc.
  Selected_By(I): I * Step;