Re: OO Style with Ada Containers

[Matthew Heaney <mheaney@on2.com>]

On Nov 20, 4:13 pm, Maciej Sobczak <see.my.homep...@gmail.com> wrote:
>
> You cannot do arithmetics with cursors. They don't have appropriate
> operators and the examples you shown work with indices, not with
> cursors. Cursors themselves can be only incremented and decremented.

Well, if it makes any difference you could write:

generic
  with package Vector_Types is
    new Ada.Containers.Vectors (<>);
  use Vector_Types;

  V : access constant Vector;  --verify this
  -- you could also try
  -- V : in Vector;

package Vector_Cursor_Operations is

  function "+" (C : Cursor; I : Index_Type'Base)
    return Cursor;

  function "-" (L, R : Cursor) return Index_Type'Base;

end Vector_Cursor_Operations;


package body Vector_Cursor_Operations is

  function "+" (C : Cursor; I : Index_Type'Base)
    return Cursor
  is
    J : Index_Type'Base;

  begin
    if Has_Element (C) then
       J := V.Last_Index + 1;
    else
       J := To_Index (C);
    end if;

    return To_Cursor (V, J + I);
  end "+";

  function "-" (L, R : Cursor) return Index_Type'Base is
  begin
    if Has_Element (L) then
       if Has_Element (R) then
          return To_Index (L) - To_Index (R);
       else
          return No_Index;  --?
       end if;
    elsif Has_Element (R) then
       return V.Last_Index + 1 - To_Index (R);
    else
       return No_Index;  --?
    end if;
  end "-";

end Vector_Cursor_Operations;

The semantics needed to be nailed down but that should give you the
general idea.  Then you can say:

procedure Op (V : Integer_Vectors.Vector) is
  package Cursor_Ops is
    new Vector_Cursor_Operations
   (Integer_Vectors,
    V'Access);  -- verify this
  use Cursor_Ops;

  Middle : constant Cursor :=
    V.First + (No_Element - V.First) / 2;

begin
  Sort (V.First, Middle);
  Sort (Middle, No_Element);
end Op;