Re: ANN: Ada 2005 Math Extensions, 20100810 release

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 11 Aug 2010 22:38:46 +0100, Simon Wright wrote:

> I was thinking about the next release, and contemplating
> 
>    --  Obtain the eigenvalues of a non-symmetric real matrix.
>    function Eigenvalues (A : Real_Matrix) return Complex_Vector;
> 
> It's easy enough to implement this in
> Ada.Numerics.Generic_Complex_Arrays.Extensions, but it seems slightly
> more natural to put it into Ada.Numerics.Generic_Real_Arrays.Extensions.
> 
> However, I'm puzzled about how to get Complex_Vector in there, because
> it's declared in Generic_Complex_Arrays (and of course you'd want to use
> the same instantiation throughout, not a local one).
> 
> Starting from the declaration of Generic_Complex_Arrays, I arrived at
> 
>    with Ada.Numerics.Generic_Complex_Arrays;
>    with Ada.Numerics.Generic_Complex_Types;
> 
>    generic
>       with package Complex_Types is new Ada.Numerics.Generic_Complex_Types
>         (Real);
>       with package Complex_Arrays is new Ada.Numerics.Generic_Complex_Arrays
>         (Generic_Real_Arrays, Complex_Types);            -- <<<<<<<<<<<<<<<<<<
>       use Complex_Arrays;
>    package Ada.Numerics.Generic_Real_Arrays.Extensions is
> 
>       function Eigenvalues (A : Real_Matrix) return Complex_Vector;
> 
>    end Ada.Numerics.Generic_Real_Arrays.Extensions;
> 
> but GNAT complains about Generic_Real_Arrays where I've indicated,
> saying it expects a package instance to instantiate a formal.
>
> I'd been hoping that -- in the context of a child of
> Generic_Real_Arrays -- the name would mean 'the current instantiation',
> but clearly not (GNAT GPL 2010, GCC 4.5.0).

AFAIK it does not work, I tried something similar before. You cannot name
the parent package instance in the generic child declarations.
 
> Any thoughts?

(as always the first thought is: what a mess generics are! (:-))

I would not do that. It would only make instantiation tricky.
Generic_Complex_Arrays already has all types involved, so for the end user
it is much simpler when the extension package were its child.

Further I would name it 

generic
package Ada.Numerics.Generic_Complex_Arrays.
   Generic_Real_Extensions;
   ^^^^
or Generic_Real_Valued_Extensions;
   ^^^^^

It is always helpful to keep all name spaces clean of generic names.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de