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From: Matthew Heaney <mheaney@on2.com>
Newsgroups: comp.lang.ada
Subject: Re: Containers - nontrivial element access
Date: Thu, 04 Oct 2007 07:01:15 -0700
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On Oct 4, 9:01 am, Georg Bauhaus <rm.tsoh+bauh...@maps.futureapps.de>
wrote:
> Why not strive for something like
>
>    swap_salary(c1, c2);
> where
>    c1, c2: Cursor;
>
> As these all are implementation level thoughts, inviting
> proper information hiding in place of hinting to mechanisms
> in function names (swap), IMHO.


Right, and you can generalize that further:

generic
   with package VT is new Vectors (<>);
   with procedure Process (I, J : VT.Element_Type);
procedure Generic_Update_Elements_By_Index
  (V    : in out Vector;
   I, J : in VT.Index_Type);


procedure Generic_Update_Elements_By_Index
  (V    : in out Vector;
   I, J : in VT.Index_Type)
is
   procedure Process_I (EI : in out ET) is
      procedure Process_J (EJ : in out ET) is
      begin
         Process (EI, EJ);
      end;
   begin
      V.Update_Element (J, Process_J'Access);
   end;
begin
   V.Update_Element (I, Process_I'Access);
end Generic_Update_Elements_By_Index;


So now you can say:

procedure Swap_Salary (I, J : in out Person) is
   S : constant Salary_Type := I.Salary;
begin
   I.Salary := J.Salary;
   J.Salary := S;
end;

procedure Swap_Salary is
  new Generic_Update_Elements_By_Index
   (People_Vectors.Vector_Type,
    Swap_Salary);

V : Vector;

Swap_Salary (V, I, J);