What is happening Here?Totally clueless

[vashwath@rediffmail.com (prashna)]

Hi all,
Have a look at the following program,
with text_io;
use text_io;
procedure TEST is 
type array_unconstrained is array(integer range <>) of integer;
subtype array_local is array_unconstrained(1..10);
array1 : array_local;
begin

   array1 := (others => 0);
   array1(1..2) := array_local'(others => (2));
                       ^^^^ can anybody what exactly is this?why they
are not assigning directly to 2 without doing this(Typecast????)
   put_line(Integer'image(array1(2)));
   put_line(Integer'image(array1(3)));
end TEST;

When I execute a constraint error is being raised.Can any body explain
what is going on here.
Thanks in advance,