Void-safety: how Eiffel removes null-pointer dereferencing
This white paper (see document as pdf) 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 failures 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 come from the programming language.
"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."
The Eiffel solution relies on a combination of language mechanisms:
- "Certified Attachment Patterns" are code schemes that the EiffelStudio compiler guarantees to be void-safe.
- "Attached types" are types that are guaranteed to have non-void values.
- The "Object Test" instruction lets programmers treat void values in a special way.
The White Paper (see the link below) describes the theoretical and practical challenges of ensuring void-safety and presents the Eiffel mechanism.