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From: "Nick Roberts" <nickroberts@adaos.worldonline.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: List container strawman
Date: Sat, 3 Nov 2001 22:30:30 -0000
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"Ted Dennison" <dennison@telepath.com> wrote in message
news:wVzE7.10194$xS6.14029@www.newsranger.com...

> I guess if the funcional stuff is going to remain in there, then it will
have to
> be a controlled type. That means that users won't be able to instantiate
it from
> within a subprogram (yuk!). If we *do* make it limited, then another issue
I
> just thought of is that we wouldn't be able to make lists of lists (we had
> already decided that we won't allow limited list components). However, I
can't
> think of a good common use for lists of lists of the top of my head.

Lists of lists are frequently useful, but the problem you suggest is easily
(and efficiently) solved by having lists of access values to lists. E.g.:


   package Item_Collections is new Collections(Game_Item);

   subtype Item_List is Item_Collections.Utility.Linked_List;

   type Game_Room is limited
      record
         ...
         Contents: Item_List;
      end record;

   type Room_Reference is access all Game_Room;

   package Room_Collections is new Collections(Room_Reference);


and so on.

--
Nick Roberts