Re: Interesting effects in array renaming

[Lutz Donnerhacke <lutz@iks-jena.de>]

* Dmitry A. Kazakov wrote:
> It povides additional safety for the reader of a program. [Isn't a goal Ada 
> design?] It would allow to omit range checks many cases like:
> 
> procedure Sum (L : in out Vector; R : Vector) is
>    subtype Of_L is Vector (L'Range);
>    RR : Of_L renames R; -- Checked here
> begin
>    for I in L'Range loop
>       L (I) := L (I) + RR (I); -- No range check needed

Currently this is not the case:

$ cat > test.adb <<END
procedure Test is
   type Vector is array (Integer range <>) of Integer;

   procedure Sum (L : in out Vector; R : Vector) is
      subtype Of_L is Vector (L'Range);
      RR : Of_L renames R; -- Checked here
   begin
      for I in L'Range loop
	 L (I) := L (I) + RR (I); -- No range check needed
      end loop;
   end Sum;
   
   a : Vector := (4 .. 10 => 4);
   b : Vector := (1, 2, 3);
begin
   Sum(a, b);
end Test;
END
$ gnatmake test
gcc -c test.adb
gnatbind -x test.ali
gnatlink test.ali
gnatlink: warning: executable name "test" may conflict with shell command
$ ./test
raised CONSTRAINT_ERROR : test.adb:10
$ sed -n 10p test.adb
         L (I) := L (I) + RR (I); -- No range check needed
$ _