Interview with Ken Arnold on Design

Bill Venners writes "Artima.com recently completed publishing a six-part interview with Ken Arnold on distributed systems, JavaSpaces, and design. In Perfection and Simplicity, Ken explains why there's no such thing as a perfect design and proposes the radical notion that programmers are people. In Taste and Aesthetics, Ken discusses the role of taste and arrogance in design, the value of other people's problems, and the virtue of simplicity. In Designing Distributed Systems, Ken addresses the concerns of distributed systems design, including the need to expect failure, avoid state, and plan for recovery. In Sway with JavaSpaces, Ken describes the basic idea of a JavaSpace, illustrates how decoupling leads to reliability. In Data, Decoupling, and Iteration, Ken explains how JavaSpaces lets you "throw in a grain and watch it grow." In Java Design Issues, Ken discusses whether to prohibit subclassing, whether to use Cloneable or copy constructors, and when to use marker interfaces."

Comments

"you want to make illegal things impossible"

[Lumpish Scholar]

Don't give people a method that does something error-prone. Give them the method that allows them to do the subset that is not error-prone. Suppose you have a file object on which you can call open and close. You can only close an open file. You shouldn't be able to call close on the file object, because it may not be open. The open method should return something on which you can invoke close. Therefore, you can't invoke close on something you have never opened, because the only thing you can invoke close on you get from open. Now you can't express the error. So you don't have to catch the error of attempting to close an unopened file, because you can't even write that.

Very cool!