Array type conversion

["Keith" <nono@joimail.net>]

What is the implementation consequence of not following  Ada reference
manual section 4.6 12/1 "The component subtypes shall statically match"?

What was the rational behind not allowing something like the following:

type some_type is new integer;
type A is array ( index_type) of integer;
type B is array ( index_type) of some_type;
Array_A:A;
Array_B:B;


declare

begin
    Array_A:=A( Array_B);

end;

Rather than the legal but more cumbersome

   for Index in index_type'range loop
      Array_A(Index):=A(Array_B(Index));
   end loop;

I know that if the component subtypes have to statically match in an array
conversion then  there is no need to check for matching constraints at run
time like Ada 83. Does this speed up execution?

But
Array_A:=A( Array_B);

seems more inline with the spirit of Ada Array operations like A+B etc.
Thanks
--
Keith