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From: mheaney@on2.com (Matthew Heaney)
Newsgroups: comp.lang.ada
Subject: Re: Adding "()" operator to Ada 200X
Date: 3 Jun 2003 07:02:48 -0700
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Fionn mac Cuimhaill <invisible@hiding.from.spam> wrote in message news:<s53odv46kst9rb73a8tsuqmgft6d7ap105@4ax.com>...
> On Mon, 02 Jun 2003 16:35:01 GMT, "Frank J. Lhota"
> <NOSPAM.lhota.adarose@verizon.net> wrote:
> 
>  To go along with this, a way to define a slice of of an
> Array_Like_Type would be nice.

But you already can do that using iterators, e.g. 

  declare
     I, J : Iterator_Type;
  begin
     Equal_Range (Multimap, Key, I, J);
     --...
  end;

Here the range [I, J) designates the contiguous range of items having
key value Key.

You can use Find and Generic_Find to generalize this to elements
(instead of just keys), and to other kinds of containers such as a
List.

Once you have the iterator pair that designates the range, then you
can iterate over the range:

  while I /= J loop
    declare
       E : Element_Type renames To_Access (I).all;
    begin
       --...
    end;

    I := Succ (I);
  end loop;

You could also use a passive iterator.  For example, if you wanted to
copy a range of items (kind of like what a traditional slice does),
then you do something like:

   declare
      Another_List : List_Subtype;

      procedure Process (I : Iterator_Type) is
         E : constant Element_Type := Element (I);
         --or E : Element_Type renames To_Access (I).all;
      begin
         Push_Back (Another_List, E);
      end;

      procedure Iterate is
         new Generic_Select_Elements (Process);
   begin
      Iterate (I, J);

      --now Another_List has a copy of the elements 
      --from List in the range [I, J)
   end;