Re: Access parameters and accessibility

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Randy Brukardt" <randy@rrsoftware.com> writes:

> Yup. With the exception of timers, all of the others stem directly from the 
> mistake of using an anonymous access for streams. And *that* stems from the 
> mistake of not allowing "in out" parameters for functions (as Input is a 
> function).

Yes, and *that* stems from the unfortunate fact that 'out' parameters
don't work like function results (for composites).

> Ergo, in Ada 2012 you would write those as "in out Root_Stream_Type'Class". 
> And one should think of them as exactly that. (It's too late to fix this 
> mistake, sadly.)

Yes.

> In the case of Timer, (a) no one ever uses this feature, and (b) I have no 
> idea why this just isn't
>
> type Timer (T : Ada.Task_Identification.Task_Id) is tagged limited private;

Because Task_Id is a private type, and unfortunately you can't have
discriminants of private type in Ada.

> But it if is actually used as an access type (with the access value being 
> copied somewhere), then you have trouble (with random Program_Errors and a 
> need to avoid passing local objects). It's possible in Ada 2012 to write a 
> precondition for this case, but of course that's not required (and surely is 
> not found in existing libraries), so the possibility doesn't help much.

Not sure what you mean.  Could you show an example of such a
precondition?

- Bob