Re: Q: Hiding the structure of a tagged type using containers

["Matthew Heaney" <mheaney@on2.com>]

brian.b.mcguinness@lmco.com wrote:
> I am trying to create a tree of object classes to represent arrays.  I
> want to hide the internal representation of the arrays in the private
> sections of the packages for the tagged types.

Yes, that's a good idea.


> However, I am having
> trouble figuring out how to do this.
> I tried this:
>
> 1
> 6  with Ada.Containers.Vectors;
> 7
> 8  package APL.Arrays.Dimensioned is
> 9
> 10    type APL_Shape is private;
> 11
> 26  private
> 27
> 28    package APL_Dimension_List is new Ada.Containers.Vectors (
> 29      Index_Type   => Dimension_Index,
> 30      Element_Type => Dimension
> 31    );
> 32
> 33    type APL_Shape is new APL_Dimension_List.Vector with null record;

Why is this a derivation?  Just say:

  type APL_Shape is record
     V : APL_Dimension_List.Vector;
  end record;



> 35    type APL_Array_Dimensioned is new APL_Array with record
> 36      Dimensions : APL_Shape;
> 37    end record;
> 38
> 39  end APL.Arrays.Dimensioned;
>
>
> Using APL_Dimension_List.Vector might work, but I am trying to
> rename this to APL_Shape in order to hide the ".Vector" part
> and make the dimension list look like a simple data type.

Fine, just implement APL_Shape as a non-tagged record with a vector
component.