Re: Language checks (Was: C++0x and Threads - a poor relation to Ada's tasking model?)

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

On Fri, 14 Aug 2009 06:33:21 -0700 (PDT), REH wrote:

> On Aug 14, 8:01�am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
>> declare
>> � �B_View : array (Index range A'Range) of Element renames B;
>> begin
> 
> I didn't know you could do that! That's very cool.

No, unfortunately it is illegal, and for all, renaming of arrays is broken
in Ada. It does not slide indices. Consider this:

with Ada.Text_IO;  use Ada.Text_IO;
procedure Test_Arrays is
   type T is array (Positive range <>) of Integer;
   subtype S is T (10..20);
   X : T (1..10) := (others => 0);
   Y : S renames X;
begin
   Ada.Text_IO.Put_Line (Integer'Image (Y'First));
end Test_Arrays;

It prints 1, instead of expected 10.

> So, as long as the
> element type and length are the same, Ada will let you change the
> index type in a rename?

Not in renaming, but in type conversion it is OK. Unfortunately type
conversions are not allowed in renaming. (But function calls are)

I think the whole issue should be revised some day...

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