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26 lines
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26 lines
1.8 KiB
Plaintext
[[Property:title|Void-safety: how Eiffel removes null-pointer dereferencing]]
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[[Property:uuid|d9380464-4312-b76e-9bfd-e57df0f59b4a]]
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This white paper (see [[file:void-safe-eiffel.pdf|document as pdf]]) presents the Eiffel void-safety mechanism, fully implemented in EiffelStudio 6.4.
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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 failures and other abnormal behaviors result from void calls.
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While extensive testing can decrease the likelihood of a void call, it cannot remove the possibility. The solution has to come from the programming language.
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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":
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:"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."
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(Citation at: [http://www.infoq.com/presentations/Null-References-The-Billion-Dollar-Mistake-Tony-Hoare] )
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The Eiffel solution relies on a combination of language mechanisms:
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*"Certified Attachment Patterns" are code schemes that the EiffelStudio compiler guarantees to be void-safe.
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*"Attached types" are types that are guaranteed to have non-void values.
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*The "Object Test" instruction lets programmers treat void values in a special way.
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The White Paper (see the link below) describes the theoretical and practical challenges of ensuring void-safety and presents the Eiffel mechanism.
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