Re: Zero length Objects

[Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>]

Nick Roberts <nick.roberts@acm.org> wrote:
: "Frank J. Lhota" <NOSPAM.lhota.adarose@verizon.net> wrote in message
: news:PSFEc.50650$aJ3.17580@nwrdny02.gnilink.net...
: 
:> No object is really of zero length. The reason is that every object should
:> have a unique address. Therefore, most Ada compilers will allocate at
: least
:> one storage element to each object, in order to insure that if we declare
:>
:>        A, B : Empty_Type;
:>
:> then A and B do not both refer to the same location.
: 
: Yes indeed.

One might add that the full story has zero size things if not
objects:

with Ada.Text_IO;

procedure sz is
   type Nothing is null record;
   for Nothing'size use 0;

   type What is record
      thing: Natural := 1_000_000;
      more: Nothing;
   end record;

   type Then_Again is record
      uhm: Nothing;
   end record;

   package TIO renames Ada.Text_IO;

   x: What;
   y: Then_Again;
begin
   TIO.put_line("size of Natural: " & Natural'image(Natural'size));
   TIO.put_line("size of x of type What: " & Natural'image(x'size));
   TIO.put_line("size of y of type Then_Again: " & Natural'image(y'size));
end sz;

$ ./sz
size of Natural:  31
size of x of type What:  32
size of y of type Then_Again:  8
$

So the size of the .more component is no greater than 1, I think.


Georg