Re: Interesting effects in array renaming

[Jeffrey Carter <spam@spam.com>]

Dmitry A. Kazakov wrote:
> ---------- test.adb
> with Ada.Text_IO;  use Ada.Text_IO;
> 
> procedure Test is
>    type Some_Array is array (Integer range <>) of Integer;
> 
>    procedure Foo (X : Some_Array) is
>       subtype Constrained is Some_Array (1..X'Length);
>       XX : Constrained renames X;
>    begin
>       Put_Line
>       (  "XX'Range:"
>       &  Integer'Image (XX'First)
>       &  ".."
>       &  Integer'Image (XX'Last)
>       &  ", Constrained'Range:"
>       &  Integer'Image (Constrained'First)
>       &  ".."
>       &  Integer'Image (Constrained'Last)
>       );
>    end Foo;
> 
>    Object : Some_Array (-3..2) := (-3, -2, -1, 0, 1, 2);
> begin
>    Foo (Object);
> end Test;
> ---------- test.adb
> 
> Surprisingly the above produces different ranges for XX and its declared 
> subtype. Isn't something wrong here?

Note that you can also do

subtype Constrained is Some_Array (1..X'Length-1);

or

subtype Constrained is Some_Array (1..3);

with similar results. You can also do

XX : Some_Array renames X;

which perhaps demonstrates more clearly where the object's subtype comes 
from.

-- 
Jeff Carter
"English bed-wetting types."
Monty Python & the Holy Grail