Random Design Patterns, Part 1

I have no special reason to start writing these, except that I've been re-reading some patterns stuff recently. And while they are "warm" in my brain, I might as well try to write them down as that always seems to help me "solidify" things. None of the patterns I'll write about are new in any way, so feel free to skip these posts you pattern gurus!

First pattern, simple as can be: Null Object. Say you have some operation that returns a Sprite object that you then do something to. What if there is no sprite? You could return NULL or nil or None or whatever your language of choice calls the thing. But then you have to check the returned value:

sprite = some_operation()
if sprite:
    sprite.do_something()

If instead you return a Sprite instance that simply doesn't do anything, your code becomes a little more straightforward:

sprite = some_operation()
sprite.do_something()

Not exactly a big deal, but of course it could add up to something more significant if you were using this in a more complicated way.

It's certainly not a good idea to always ignore the fact that you didn't find the sprite in question, for example you don't want to keep inserting NullSprite objects into a list over and over. So when you do care, you need a way of telling that it's a real sprite. One way is to guarantee that only a single NullSprite is ever created and to make that one globally accessible. Then, in places where you care, you can say this:

sprite = some_operation()
if sprite is not Sprite.NULL:
    sprite.do_something()

Whether Null Object is particularly useful therefore depends on how often you care versus how often you don't care (but still have to check if you use the language's builtin version of "no such object"). As with all design patterns: Think before you apply the pattern!