Re: Persistence of limited tagged types

[mheaney@on2.com (Matthew Heaney)]

Nick Roberts <nickroberts@blueyonder.co.uk> wrote in message news:<oprm9kpdkkbqmqul@news.cis.dfn.de>...
> 
> Speaking (all right writing) 'off the cuff' as it were, my attitude is that 
> limited types are (supposed to be) inherently not the kind of types which 
> are persistent (serialisable).
> 
> I would expect your type (hierarchy) to be non-limited if it is 
> serialisable; possibly this is a slightly purist point of view.
 
Is T'Output available if type T is limited?

GNAT lets me declare an output operation:

  type T is limited null record;

  procedure Output 
    (Stream : access Root_Stream_Type'Class;
     Item   : in     T);

  for T'Output use Output;

but then it refuses to let me call it:

   O : T;
begin
   T'Output (Stream, O);
end;

I get an error message that "limited type T has no stream attributes."

However, if I define T'Write, then GNAT compiles

  T'Write (Stream, O);

without complaint.

What's up with that?  Is the expectation that T'Output can't be used
for a limited type?  Why does GNAT allow me to define the T'Output
stream attribute?