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From: Ted Dennison<dennison@telepath.com>
References: <DzdP7.48986$xS6.81471@www.newsranger.com>
 <hRdP7.49017$xS6.81420@www.newsranger.com> <3C0E1FA1.45A38A75@brighton.ac.uk>
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 <DpxP7.50285$xS6.83694@www.newsranger.com> <DxyP7.309$w85.20109@rwcrnsc54>
 <CALP7.51313$xS6.84388@www.newsranger.com>
Subject: Re: Iterator approach (was: List container strawman 1.3)
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Date: Thu, 06 Dec 2001 16:19:18 GMT
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Date: 2001-12-06T16:19:18+00:00
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In article <CALP7.51313$xS6.84388@www.newsranger.com>, Ted Dennison says...
>
>In article <DxyP7.309$w85.20109@rwcrnsc54>, Mark Lundquist says...
>>In the access discriminator way, any state of affairs that could give rise
>>to a dangling iterator results in a compile-time error, and the safety comes
>>at no added run-time expense.  The chained iterator approach results in a
>
>I don't think that's true at all. Suppose I have the following (using your
>example):
>
>.   type List_Ptr     is access My_Lists.List;
>.   type Iterator_Ptr is access My_Lists.Iterator;
>.   function Free is new Unchecked_Deallocation (My_Lists.List, List_Ptr);
>.   function Free is new Unchecked_Deallocation (My_Lists.Iterator,
>Iterator_Ptr);  


Damn. Got cut off again.

The idea here is that I dynamicly allocate both the list and an associated
iterator, then use Free to deallocate only one of them. I don't believe the
compiler would give that code any error, and I end up having a pointer to
nowhere that the List facility has no way to detect. Not "safe".

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

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