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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Operation can be dispatching in only one type
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Date: Thu, 19 Nov 2009 09:50:29 +0100
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On Wed, 18 Nov 2009 18:27:42 -0600, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:1wtsriaxu0s4s$.ikwnnz5teukp$.dlg@40tude.net...
> ...
>>> OK, I don't understand this.  First, I don't understand what about
>>> accessibility checks was a disaster;
>>
>> Because they are the major contributor to hours spent on debugging
>> unhandled exceptions.
> 
> That seems odd to me. I rather *like* getting unhandled exceptions, because 
> it is almost always easy to see what the problem is from the exception name 
> and the traceback.

Only theoretically. Practically, the existing handlers of "legal"
exceptions get perplexed, the stack gets wound up causing a cascade of
exceptions in Finalize's.

> OTOH, doing something that even generates a runtime accessibility check is a 
> bug 

Isn't it an advise to use only 'Unchecked_Access? (:-))

I think it is a problem that the code containing 'Access or upcast pointer
type conversions is "suspicious", a subject of careful inspection for false
positives upon accessibility check:

   Upcast_Ptr (P)   -- Unsafe
   P.all'Access        -- Unsafe
   P.all'Unchecked_Access   -- "Safe"

> IMHO (it's what Bob Duff calls a "tripping hazard" - a latent problem 
> that will bite you when someone does something unconventional -- in that 
> sense it is just like the bug of assigning a string parameter has lower 
> bound 1); it would be useful if the compiler could optionally point out such 
> places so you could fix them.

The difference is that for string bound there is a way to do it safe and
for 'Access there is none (and I also agree with Robert's response.)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de