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From: porton@ex-code.com (Victor Porton)
Date: Fri, 08 Nov 2002 10:21:15 +0500
References: <3dc92622$0$308$bed64819@news.gradwell.net>
Subject: Re: Booch: missing r/w access through iterators
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In article <x7vn0ol148m.fsf@smaug.pushface.org>,
	Simon Wright <simon@pushface.org> writes:
> porton@ex-code.com (Victor Porton) writes:
> 
>> I noticed Access_Current_Item, but with it to gain such access one
>> needs to create a new procedure! Too bad. I want direct access like:
>> 
>> function Current_Item_Access(It: Iterator'Class) return Item_Access;
> 
> I can see why you might want it, and at the moment I can't remember
> why it's not there. Perhaps something to do with the problem of
> creating the access value? (it would force the item in the Container
> to be aliased, thus constraining it .. I know this actually happens in
> the BCs but I was very unhappy with the necessary kluge).

So, if you insist on not aliased container items in general, you 
however can (and please do so):

1. Add procedure to assign a value to the current item:

procedure Assign_Current_Item (It : Iterator; Value : Item) is abstract;
-- Alternatively it can be not abstract but using Iterator_Operations
-- (see below).

2. For every iterator type add the following generic subpackage (in the
same package as the corresponding iterator type):

generic
   It: in out Iterator'Class;
package Iterator_Operations is

   Element: Item renames ...;
   -- The container element to which It refers.
   
end Iterator_Operations;

where "..." is different for each iterator type.