Re: REQ: Extend slices for n dimensional arrays for Ada 202X

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 26/01/2017 15:01, Lucretia wrote:
> On Thursday, 26 January 2017 13:29:47 UTC, Lucretia  wrote:
>
>>
>>   Texture (x1 .. x2, y1 .. y2) := Buffer;  --  Buffer is the correct size.
>
> I forgot to mention something else. I put the above notation down as
> someone in #Ada liked tha, but I would prefer the following:
>
>   Texture (x1, y1 .. x2, y2) := Buffer;  --  Buffer is the correct size.

I don't understand the latter. (X1, Y1) .. (X2, Y2) is not a submatrix 
it is a linear slice:

  I   1 2 3 4
      -------
  1 | a b c d
  2 | e f g h
  3 | i j k l
  4 | m n o p

Submatrix 1..2, 2..4 is

      1 2 3
      -----
  1 | b c d
  2 | f g h

(1,2) .. (2,4) is a vector

  1 | b
  2 | c
  3 | d
  4 | e
  5 | f
  6 | g
  7 | h

> The reasoning is as follows:
>
> 1) That is easier for people to visualise.
> 2) That follows how n-dimensional arrays are accessed in Ada, i.e.
>
>   procedure Test is
>      type Matrix is array (1 .. 4, 1 .. 4) of Float;
>
>      I : Matrix;
>   begin
>      I (1, 4) := 0.0;
>   end Test;

It does not follow. The indexing notation is as a tuple

    I1 x I2 x ... x IN

Where Ik is either a singleton (collapsed dimension) or a subset of the 
index (in Ada a range).

With generic subsets I ({1,2},{2,4}) would mean

       1 2
       ---
   1 | b d
   2 | f g

You forgot notation for whole index range:

   I (<>, 1)  -- column 1.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de