Re: Two ideas for the next Ada Standard

[bobduff@world.std.com (Robert A Duff)]

In article <JSA.96Sep7202332@alexandria>, Jon S Anthony <jsa@alexandria> wrote:
>In article <323153E7.2CDA@joy.ericsson.se> Jonas Nygren <jonas@joy.ericsson.se> writes:
...
>But, as long as this particular case was used, I actually have a question
>for Bob (if he is reading this...)  Why didn't the generic signature for
>System.Address_To_Access_Conversions include the access type?

It probably should have been.  It was discussed, and I think the design
team basicall said, yeah, we know that it's usually best to pass in the
access type, to avoid unnecessary conversions, but in this case, you're
doing low-level hacking anyway, so a few extra conversions won't hurt.

>> One solution to this could be to provide an 'anonymous general
>> access-to-variable type', RM6.1(24), for variables to and not only
>> for subprogram formals and discriminants. Perhaps one could use a
>> syntax similar to T'Class and have T'Access denoting this new
>> subtype. With this syntax we could have the example from above:
>
>I _think_ Bob Duff would agree with you, ...

Yes.

>... but I still don't see this
>as a problem so would not agree with it.  In fact, I see the current
>situation of not having this as a _good_ thing not just a "shrug".

The examples we're discussing are not a real problem, because you can
avoid the conversions by simply using the same type, and pass it around
to generics.  But when you use a lot of access-to-class-wide types, it
*is* a problem, because you *have* to declare a bunch of different
access types.  Conversions in the upward direction are a real pain,
IMHO.

- Bob