Stephan Murer
Clemens Szyperski
Abstract
Sather extends the notion of an iterator in a powerful new way. We argue that iteration abstractions belong in class interfaces on an equal footing with routines. Sather iterators were derived from CLU iterators but are much more flexible and better suited for object-oriented programming. We retain the property that iterators are structured, i.e., strictly bound to a controlling structured statement. We motivate and describe the construct along with several simple examples. We compare it with iteration based on CLU iterators, cursors, riders, streams, series, generators, coroutines, blocks, closures, and lambda expressions. Finally, we describe experiences with iterators in the Sather compiler and libraries.
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Index Terms
- Iteration abstraction in Sather
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Reviews
Arthur Gittleman
Sather is an object-oriented language derived from Eiffel. Sather iterators, described here, derive from CLU but remove some limitations of CLU iterators, such as there being one iterator per loop; there being no way to modify elements; and iterator arguments being loop invariant. In Sather, multiple iterators may be invoked within a single loop, and there are hot arguments that are reevaluated each time control is passed back to the iterator. Several examples in section 2 show the power and ease of use of Sather iterators. Section 3 gives the details of the iterator construct. In section 4, the authors compare Sather iterators with other approaches. They find that: cursors are harder to use; built-in loop constructs are not general enough; passing of closures does not effectively support the simultaneous traversal of multiple data structures; and streams come closest to Sather iterators, but are not bound to a specific loop. Analyzing a Sather compiler written in Sather showed many uses of nontrivial Sather iterators, making the code simpler and easier to read. The authors conclude that iterators eliminate common errors by combining initialization, progression, and termination into one abstraction that does not need to be managed by client code. In this well-written paper, the authors make an excellent case for Sather iterators.
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