Re: Run-time accessibility checks

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

On Dec 7, 9:44 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Sat, 6 Dec 2008 09:10:49 -0800 (PST), Ludovic Brenta wrote:
> > Dmitry A. Kazakov wrote:
> >> It is absolutely unacceptable to me that a correct
> >> program might fail at run-time because of accessibility checks.
>
> > I differ here; to me, a program that fails an accessibility check at
> > run time is incorrect.
>
> Ah, I used to think this way too. But then I realized that this form of
> constraint is not a semantic one. Comparing to the constraint range 1..10,
> accessibility constraint is an implementation detail. It has no semantic
> meaning. When you assign a value outside the range that is semantically
> incorrect. When you assign a pointer that potentially might become
> dangling, that has no semantic meaning. The pointer is not yet dangling.
> The program correctness depends on whether it will become dangling.

My definition of correctness is a bit more demanding. I want to be
*certain* that the pointer *cannot* become dangling, *ever*,
especially in the face of software maintenance where the program
changes. That's what accessibility checks give me, and I am grateful
for their existence and I will design my programs so as not to fail
accessibility checks.

--
Ludovic Brenta.