Re: ObjectAda vs Gnat -- bugs

["Nick Roberts" <Nick.Roberts@dial.pipex.com>]

Jon S Anthony <jsa@alexandria> wrote in article
<JSA.97May19145513@alexandria>...
> In article <5loibn$qek@lotho.delphi.com> tmoran@bix.com writes:
> 
> > So if I wanted to make some reusable object with the characteristics:
> >   constant once created
> >   creation requires info not conveniently done with discriminants
> >   limited
> > one approach would be to make the type T limited and tell users to
declare
> >   X : T renames Create(...);
> > Right?
> 
> Works for me...
> 


No, I don't agree. I think the "renames" is potentially misleading. An
alternative approach would be:

      X: T; -- X initialised to an unusable status
   begin
      Init(X,...); -- X now set up as required

The first parameter of procedure X would be of type "in out T". This may be
uglier than the above solution, but it would be less misleading, and it
might be more flexible in some situations (as arbitrary processing can
precede the call to Init). Any attempt to use X before it had been properly
set up could be detected and raise an exception. If X needs to be constant
once set up, any attempt to call Init again on X could also be detected and
raise and exception.

Nick.