I have been until now a fervent disciple of compositing a graphic instance into a class in every case, rather than making my class extend MovieClip. Admittedly I was a piker at AS2 and only now that I am cranking on AS3 do I consider myself worthy to call myself a beginner OOP programmer. But I bought into all the reasons, and if I were still making AS2 apps, I might remain in that camp.
But lately my devotion has been shaken and now I am seriously considering extending (and then subclassing from) MovieClip or Sprite when making any class which has a visual component. Whereas before I would always compose in a MC instance, almost never make my class inherit from anything but my own superclass, and implement interfaces for polymorphism, now I think I will extend, although still implement interfaces for the usual other reasons. I also still plan to be a composition devotee in all other ways-- I like composition more than inheritance. Also I would not extend MC for classes which have no graphical component, such as game logic components. (I am making games and other interactive entertainment apps, for in-browser distribution.)
Can I please be illuminated by better coders than I as to the wisdom or folly of my change of heart?
Here are a few reasons why my mind is changing; please feel free to refute or support any of these:
–Changes between AS2 and AS3 make the downside of subclassing MC/Sprite smaller than before. I’ll let far more informed people come up with good examples, but one seems to be the explicit nature of adding an object to the display list-- the overhead hit of being an MC is small (nonexistent?) if it is not on the list.
–Colin Moock, in his seminal “Essential ActionScript 2” book, advocated composition-- see his large MVC example in which his view class, although nearly entirely visual in function, did not extend MC but rather composited MC. However, in Moock’s equally impressive AS3 book, all his examples now seem to use extension. I really admire Moock so this gives me a new perspective.
–All the Adobe best practices and examples use extension, as do nearly all code samples I see in other helpful forums. I am not one to blindly run with the crowd but I think I’d get better feedback on my code from my peers if I follow suit.
–All the AS3 Flash components seem to use extension, and indeed, AS3 itself is heavily inheritance-based rather than composition-based, for understandable reasons.
I am probably missing a lot and mis-stating much of what is there but hopefully you get the idea.
So once again I ask my better peers: what are now the arguments for and against extending MC or Sprite for one’s visually represented classes in AS3? Any observations would be much appreciated.
