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Subject: Re: My bug or else regarding Visibility Rules
From: Anh Vo <anhvofrcaus@gmail.com>
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Date: 2013-04-04T12:21:29-07:00
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On Thursday, April 4, 2013 1:19:54 AM UTC-7, Simon Wright wrote:
> Anh Vo <anhvofrcaus@gmail.com> writes: > On Tuesday, April 2, 2013 1:16:34 PM UTC-7, Simon Wright wrote:

>> I believe that attribute 'Old is allowed in post-conditions only. 

> This is a bug in GNAT, fixed in GCC 4.8.0 (I had tested with GNAT GPL 
> 2012, which allows it). 

It is good to know.

>> I do not understand this. Why isn't Buffer(1) valid if my index starts at 1? 

> Because after the index has wrapped round Buffer'Old(1) will not be the 
> same as Buffer(1). 

In this case the loop will drop out because loop lower end is greater than loop upper end.

>> This is another array index option. 

> No. You wrote 
>   (Index mod Length) + 1 
> but it should be 
>   (Index + 1) mod Length 

(In_Index + 1) mod length will raise Constraint_Error when the Queue is just full. In fact, (10 + 1) > 10 when the queue has the lenght of 10.