Avoid a Void: The Eradication of Null Dereferencing

Ending null pointer crashes

“…The original article describing void safety (and giving credit to other languages for some of the original ideas) was a keynote at ECOOP in 2005 3 . Revisiting the solution some years later, I wrote 4 :…”

Negative Variables and the Essence of Object-Oriented Programming

“…For any variable x that may be used as target of a qualified call, the "negation" of x, written x', denotes a reference, defined during the execution of a qualified call of target x, to the object that started this call. (The existence of such an object is traditionally checked at run time, through "null pointer" exceptions, but in some recent languages it has become a static property enforced by the compiler, as in Eiffel's "void safety" mechanism [9]. The present discussion assumes that all calls are voidsafe, i.e.…”

“…The target's attachment status ensures that a call cannot lead to an exception at run-time. Meyer, Kogtenkov and Stapf address this issue in [9]; in the examples we have taken the assumption of attachment for granted. The other key property presented in [14] can be deduced, as we have seen, from the general rules for negative variables.…”

Towards a Calculus of Object Programs

“…A Java or C# programmer might write the call previous.set_right (temp) as a remote assignment previous.right := temp, but we restrict ourselves to a proper form of O-O programming which rules out such violations of information hiding: the only way to set a field of another next previous object is through a setter procedure such as set_right. The detachable declaration marks variables whose value might be void [14].…”

“…References can be "void" (or "null"). We do not need to concern ourselves with the problem of "void calls" (or "null-pointer dereferencing"), even in the absence of a mechanism as Eiffel's Void Safety which removes it entirely at compile time [14], since the conventions defined below will ensure that no void reference is used in an unsafe way.…”