Abstract

How should iterators be abstracted and encapsulated in modern imperative languages, e.g., Ada and C++? We consider the combined impact of several factors on this question: the need for a "common interface model" for userdefined iterator abstractions; the importance of formal methods in specifying such a model; and problems involved in modular correctness proofs of iterator implementations and clients. A series of iterator designs illustrates the advantages of the "swapping paradigm" over designs based on the traditional "copying paradigm." Specifically, swapping-based designs admit more efficient implementations, while offering straightforward formal specifications and the potential for modular reasoning about program behavior. The final proposed design schema defines a common interface model for iterators for a wide variety of generic collection abstractions in languages such as Ada and C++. Index Terms --- Formal specification, iterator, program verification, proof of correctness, sw...

Citations