Re: Persistence of limited tagged types

[Nick Roberts <nickroberts@blueyonder.co.uk>]

On 9 Apr 2003 16:09:09 -0700, Matthew Heaney <mheaney@on2.com> wrote:

> Is T'Output available if type T is limited?

According to the RM95 (13.13 (36)) (which I'm certain you must have already 
consulted, Matt) the stream-oriented attributes (Read, Write, Input, 
Output) are defined for all types, but defaults are not provided for 
limited types.

> 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 [but not call it]?

I don't immediately see how this (GNAT's) behaviour obeys the standard.

It could be argued that since T in this example is a definite type, it is 
not actually necessary to define or call T'Output, since T'Write could be 
defined and called instead with the same effect. But I don't see how this 
could permit GNAT to produce the error it does.

Perhaps I should ask which version of GNAT this was, and do some tests 
myself?

-- 
Nick Roberts
Jabber: debater@charente.de [ICQ: 159718630]