Re: What would you like in Ada202X?

[Adam Beneschan <adam@irvine.com>]

On Friday, June 29, 2012 4:54:55 AM UTC-7, AdaMagica wrote:
> On Friday, June 29, 2012 1:29:03 PM UTC+2, (unknown) wrote:
> > 1. Want to see parameter modes in calls.
> >
> > procedure Proc (An_In_Parameter     : in     Integer;
> >                 An_Out_Parameter    :    out Integer;
> >                 An_Inout_Parameter  : in out Integer;
> >                 An_Access_Parameter : access Integer);
> >
> > Proc (An_In_Parameter     <=  A,
> >       An_Out_Parameter     => B,
> >       An_Inout_Parameter  <=> C,
> >       An_Access_Parameter  -> D'Access);
> >
> > A becomes An_In_Parameter, An_Out_Parameter becomes B, etc.
> 
> I've often wished that be possible. However "<=" is already defined as a relational operator "less or equal". so <== or something like that would be needed. ("Greater or equal" is ">=", so there is no problem, but for consistency ==> would then perhaps be better.)
> 
> > 2. Expressions with Discriminants.
> >
> > type Symmetric_Matrix (Dim : Natural) is record
> >   Values : Float_Array (1 .. Dim * (Dim + 1) / 2;
> > end record;
> 
> Also this would be nice. However then the upper bound would have to be stored as a hidden record component as well, I guess, and this would conflict with respresentation clauses (how to handle hidden components).

The solution is simple: don't allow record representation clauses in cases like that.  I can't imagine anyone wanting to define a record of this nature anyway in a situation where the representation has to be specified exactly because the record is used by code in some other language, or something like that.

(I think implementors are already allowed to reject representation clauses they can't handle, and they're allowed to come up with fake names for hidden components in record rep clauses.  The real reason expressions involving discriminants aren't allowed was, I think, because back when Ada 83 was designed they were thought to add too much complexity for implementors.  Or something like that... I'm not entirely sure.)

                             -- Adam