Re: Can Ada iterate over Nd array?

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

On 04/25/2012 09:42 PM, Okasu wrote:
> I can't iterate over Nd array in Ada, becuse of
>> expression for dimension must be static
> So following code won't work:
>
> for X in A'Range loop
>     for Y in A'Range (X) loop
>        null;
>     end loop;
> end loop;
>
> Geez, guys, what if i have to work with 1000d array?
> How can i iterate over it?

I have no idea what you're trying to do.

Obviously you're expecting A to be square (or cubic, or hyper-cubic, or ...), to 
have indices of an integer type, and to have lower bounds of 1. None of these 
are necessarily true.

Multi-dimensional arrays need not be square, so A'range (X) might reference 
dimensions of A that don't exist (if it were allowed).

Array indices can be of any discreet type, including enumeration types. I don't 
know what A'range (Green) or A'range ('E') would mean.

Even if an array has integral indices, the lower bound need not be 1. Again, 
A'range (X) might reference dimensions of A that don't exist.

I can't see what you'd have in place of "null;" for a 1000-dimension array. You 
can reference the whole array (A) or index a specific component of A, which 
requires as many indices as A has dimensions. You have 2 indices, X and Y; where 
are you going to get the other 998 indices?

In general, you iterate over an N-dimensional by having N nested "for" loops, 1 
for each dimension of the array:

type Three_D is array (1 .. 3, 7 .. 300, 'A' .. 'Z') of Integer;

A : Three_D;

for I in A'range (1) loop
    for J in A'range (2) loop
       for K in A'range (3) loop
          -- Do something with A (I, J, K)
       end loop;
    end loop;
end loop;

-- 
Jeff Carter
"Ada has made you lazy and careless. You can write programs in C that
are just as safe by the simple application of super-human diligence."
E. Robert Tisdale
72