Saint Singleton
In our book, I wrote the chapter on the Singleton Design Pattern, and on this blog I penned the post entitled, We Don’t Need No Stinkin’ Singletons. My comments were based on several articles (including one similarly named!) I had read on why to avoid the Singleton and the 2006 OOPSLA meetings in Portland, Oregon. Of the articles available online that detail the problems with the Singleton Miško Hevery’s blog post, Singletons are Pathological Liars is the most detailed, but Scott Densmore’s article, Why Singletons are Evil is an equally convincing—and succinct— argument why we should keep our distance from Singletons.
Even Erich Gamma was quoted as lamenting the fact that they included the Singleton in their Design Pattern book. There’s not a lot more that I can say than I did in my ranting post on Stinkin’ Singletons, and you can find tons more online.
Is There Salvation?
Recently on this blog, my old friend aYo Binite (who got me involved in ActionScript 3.0 design patterns in the first place) suggested that the Singleton wasn’t as bad as I made it out to be. Naturally, I replied with a reasonable argument comparing them to skin-eating viruses, pedophiles, and Nazis. aYo said that the jury was still out, and I wondered, ‘What jury?’ All in all, though, I may have been as unfair to the Singleton as the Roman emperor Diocletian was to Saint Sebastian. (Diocletian first had Sebastian used for archery practice and left him for dead. Then when the emperor found that he had survived—he had Sebastian beaten to death and thrown into a crapper.) Naturally, I don’t want to be equated with the touchy Diocletian, and so I’m offering up an opportunity for comments by our readers to either help pull the Singleton out of the crapper or shoot another arrow into the misguided design pattern. The Comment Section is Open!
At the 2006 OOPSLA Conference in Portland, Oregon one of the people who came into our session was pounding on the Singleton Design Pattern. He even brought in a PowerPoint presentation quoting Erich Gamma as saying he wished he’d never included the Singleton in the GoF book. This wasn’t a mild rebuff of the Singleton; it was a wholesale condemnation.
The Singleton in ActionScript 3.0
A quick online search reveals a good deal of discussion about the Singleton in ActionScript 3. However, much of that discussion is based on how to improve it given AS3’s lack of private class constructors. Both Grant Skinner and Tink have provided brilliant workarounds that seem to solve the problem of multiple instantiations of a Singleton. Darron Schall has written a nice summary of the ActionScript 3.0 Singleton discussions and reached a similar conclusion as I originally did. Namely, most of the problems envisioned by ActionScript 3.0’s lack of private class constructors never caused the problems that AS3’s shortcomings were supposed to have caused. In our book, we provide a brief cautionary tale about using the Singleton, but it was not very strong or substantive. (I wrote the Singleton chapter; so I can say that.)
Any attempt to improve the Singleton is like making the black mamba more deadly. The point is not to improve it but to avoid it. However, in understanding the problems using the Singleton, we can better understand what the focus of OOP programming should be and the reason that using design patterns is important for achieving the dual goals of change and re-usability. A lot of the criticisms of the Singleton have been summarized by Scott Densmore and on the Flash-Focus blog, and my intention is not to improve on their comments. Rather, I’d like to use the general comments by them and others to focus on good practices and re-focus the discussion of design patterns to the key issues important to OOP and design patterns. That focus, I believe, is the relationship between objects.
Continue reading ‘We Don’t Need No Stinkin’ Singletons: Why to Avoid the Singleton Pattern in ActionScript 3.0 Programming’
Bill Sanders
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