Joseph N. Wilson

Dylan's Differing World View

The fundamental difference between the Dylan view of object behavior and that espoused by Smalltalk hinges on how one elicits behavior. In the Smalltalk view, classes contain an enumeration of the data members each instance will contain and also contain the methods used by the class to implement messages it will receive. The Dylan view, removes the methods from the classes, and groups them together in what are termed generic functions. A generic function is associated with the methods which implement it, rather than associating methods with the objects.

Dylan's view, though characterized by some as non-OO, supports a valid and reasonable view of how to achieve computation in an OO framework. In particular, Dylan's view solves problems associated with more traditional message-passing implementations. (See the double-dispatchwork-around cited by Budd in Chapter 8 as an example of something that can be avoided easily in Dylan.) Dylan's view also supports multiple-inheritance in a straighforward and principled way.