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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Ada.Numerics.Long_Real_Arrays
Date: Thu, 26 Jan 2017 14:52:56 +0000
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Date: 2017-01-26T14:52:56+00:00
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This will compile, and preserve visibility of the underlying Vectors.
I'm not sure whether one could get something less clumsy by using
Ada.Containers.Indefinite_Vectors to hold the R_Vectors.

with Ada.Numerics.Long_Real_Arrays;
generic
   Np : Positive;
package Nm_G is
   subtype R_Vector
     is Ada.Numerics.Long_Real_Arrays.Real_Vector (1 .. Np);
   type R_Matrix is array (1 .. Np + 1) of R_Vector;
end Nm_G;

with Nm_G;
package Nm is
   --  I assume there's more than just Fnm here; if not, Fnm could be a
   --  library-level generic subprogram.
   --
   --  Of course, if there _is_ more than just Fnm, it's likely the
   --  other components will also need to know which instantiation of
   --  Nm_G they have to deal with, and the 'with package' bit would
   --  need to be placed on the Nm (which itself has to be generic).
   generic
      --  This generic needs to know which instantiation of Nm_G it is
      --  to deal with.
      with package Nm_I is new Nm_G (<>);
      --  Now we know what type the parameter of the actual F has to
      --  be.
      with function F (R : Nm_I.R_Vector) return Long_Float;
   procedure Fnm (P : in out Nm_I.R_Matrix);
end Nm;

package body Nm is
   procedure Fnm (P : in out Nm_I.R_Matrix) is
   begin
      null;
   end Fnm;
end Nm;

with Nm;
with Nm_G;
procedure Test_Nm is
   package Nm_Inst is new Nm_G (Np => 2);
   function Actual_F (R : Nm_Inst.R_Vector) return Long_Float is (42.0);
   procedure Actual_Fnm is new Nm.Fnm (Nm_I => Nm_Inst,
                                       F    => Actual_F);
   P : Nm_Inst.R_Matrix := ((1.0, 2.0), (3.0, 4.0), (5.0, 6.0));
begin
   Actual_Fnm (P);
end Test_Nm;