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Author:bmeyer

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Date:2009-08-04T17:01:43.000000Z


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documentation/current/papers/void-safety-how-eiffel-removes-null-pointer-dereferencing.wiki
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[[Property:title|Void safety]]
[[Property:title|Void safety: how Eiffel removes void references]]
[[Property:link_title|Void-safety: how Eiffel removes null-pointer dereferencing]]
[[Property:weight|0]]
[[Property:uuid|d9380464-4312-b76e-9bfd-e57df0f59b4a]]
Here is the paper.
This white paper (see link below) presents the Eiffel void safety mechanism, fully implemented in EiffelStudio 6.4.
In almost every program running today there is a ticking time bomb: the risk of a "void call". A void call is possible in programs written in almost any programming language; its effect is usually to crash the program. Many unexplained program crashes and other abnormal behaviors result from void calls. While extensive testing can decrease the likelihood of a void call, it cannot remove the possibility. The solution has to com from the programming language.
<!--break-->
Professor C.A.R. Hoare from Microsoft Research, winner of the Turing Award and the Kyoto Prize, calls the presence of void calls in modern programming languages the "billion-dollar mistake":
<ul>"The invention of the null reference in 1965" [the source of void calls] "has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years."
</ul>
(Citation at: http://qconlondon.com/london-2009/presentation/Null+References:+The+Billion+Dollar+Mistake</a>.)
The Eiffel solution relies on a combination of language mechanisms:
<ul><li>
"Certified Attachment Patterns" are code schemes that the EiffelStudio compiler guarantees to be void-safe.
<li>"Attached types" are types that are guaranteed to have non-void values.
<li>The "Object Test" instruction lets programmers treat void values in a special way.
</ul>
The White Paper describes the theoretical and practical challenges of ensuring void safety and presents the Eiffel mechanism.