Re: Half Constrained Array Types and Slices

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

Robert A Duff wrote:
> 
> I don't quite see the point of this.  If 'Length = 0,
> it seems to me, then the index type must be some sort of integer,
> or something like that.  It depends on how far afield you want
> to go.  For example, do you like "array(String range <>) of Integer"?
> There's no _range_ there...

I think the index type should be discrete. But surely it doesn't need to be an 
integer:

with Ada.Text_IO;
procedure Null_Range is
    type A is (B, C);

    type D is array (A range <>) of Integer;

    E : D (C .. B);
begin -- Null_Range
    Ada.Text_IO.Put_Line (Item => A'Image (E'Last) );
end Null_Range;

This is valid Ada. With GNAT, it outputs B. However, if D were a string type, "" 
would not be valid for it.

> The idea that 'Range is equivalent to 'First..'Last seems reasonable to
> me...

I'm not saying it's a good idea. I'm just wondering what the consequences of it are.

-- 
Jeff Carter
"Crucifixion's a doddle."
Monty Python's Life of Brian
82