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

[Lucretia <laguest9000@googlemail.com>]

On Thursday, 26 January 2017 14:52:04 UTC, Dmitry A. Kazakov  wrote:
> 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:

You're being deliberately obtuse. I even spelt out the semantics above. The language designers spell out the semantics of the language constructs as I did.

For the 1D case, we define an array as:

  type Some_Array is array (Positive range 1 .. 5) of Integer;

Access an element with:

  T : Some_Array;

  T (4) := 3;

Slice with:

  S : Some_Array := T (2 .. 4);

For the 2D and above case, we define an array as:

  type Some_Array is array (Positive range 1 .. 5, Positive range 1 .. 10) of Integer;

Access an element with:

  T : Some_Array;

  T (1, 1) := 3;

So we could slice with:

  S : Some_Array := T (2, 2 .. 4, 6);  -- Square slice!

So in the following case (row-major order):

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

A slice of (2,2 .. 3,4) would give:

  | 1 2
-------
1 | f j
2 | g k
3 | h l

Not a linear vector, because that's not the semantics I'm looking for, is it?

> 
> You forgot notation for whole index range:
> 
>    I (<>, 1)  -- column 1.

This is irrelevant as you cannot assign I (<>) in the 1D case anyway.

Luke.