Static initializers in AS3

Dec 20

The problem

Today while refactoring some global static classes code to be more manageable at work thought of one thing. Thing is that those classes stuff often should get initialized. Where initialization it is usually called? Well who knows, anywhere where it fits… With big project where you have many global managers like money manager, hints manager, events manager etc etc their initializers are usually hidden somewhere while they are used in multiple places. Now often it happens that something changes and needs to access that class sooner then it was needed before. What follow is probably null reference error or something similar. And now you need to go, figure out where it is initialized now, what needs to be done to initialize it sooner. Or just try to move code that needs it to some later stage… Sounds bad right? Some spaghetti code stuff in project where multiple programmers work on same code base. Especially when stuff in those global classes needs to be called in various places that can come at random order depending on server and user input.

Static initializers in AS3

So refactoring stuff I was thinking about this problem again. Interesting thing about Flash is that it uses lazy static class initialization. In short that means that static class is not initialized until it is referenced somewhere in code. Neat feature though still a compromise. We get start up performance as not all classes are initialized from the start but then we loose some as each time class is referenced there is a check for it being initialized(I guess, that’s how it usually is done). Now that’s good but what if we need not only to initialize variable but run some code. For example some parsing of variables content. Google for the rescue: Static initializers. Nice, short and clear article.

{

//put code that will be called when class if referenced for first time

}

There is one thing though. You can debug code inside those brackets. So I instead just put a call for some static function which I can debug then.

So now I have something like that:

public class GlobalMoneyManager

{

public static var PricesXML:XML;//set when loaded

{

Init();//initialization code called

}

public static function Init():void

{

//parsing prices, calling stuff, etc

}

}

Now then it works for me like that.

Site/Game loads and XML with info is loaded.
Then there are like 10 UIs that use information that needs to be retrieved from that XML but none of them is shown at the start
When user action results in one of those UIs showing up, UI is initialize and reference something in GlobalMoneyManager
GlobalMoneyManager is initialized
Static initializer code is called
Init is called and class if filled with parsed info
Control is returned to UI and data is accessed

The end

Works like magic. I wonder if there is a catch to this that would make it a bad coding style that raises more problems then it solves. So far I do not see any.

none

Damian

Have you thought about using the Singleton pattern? You keep your static accessibility etc, but you gain the flexibility of having a class instance that’s created the first time you access it. Using your example above you could write the code like:

public class GlobalMoneyManager
{

private static var m_creating:Boolean = false;
private static var m_instance:GlobalMoneyManager = null;

public static get instance():GlobalMoneyManager
{
if( GlobalMoneyManager.m_instance == null )
{
GlobalMoneyManager.m_creating = true;
GlobalMoneyManager.m_instance = new GlobalMoneyManager;
GlobalMoneyManager.m_instance._init();
GlobalMoneyManager.m_creating = false;
}
return GlobalMoneyManager.m_instance;
}

public function set pricesXML( x:XML ):void
{
…
}

public function GlobalMoneyManager()
{
if( !GlobalMoneyManager.m_creating )
throw new Exception( “The GlobalMoneyManager is a Singleton! Use GlobalMoneyManager.instance instead” );
}

private function _init():void
{
// do init stuff here
}
}

Then you can simply set your xml with:

GlobalMoneyManager.instance.xml = …;

The class is created automatically and the init() (now private) gets called no matter who calls it first. Much cleaner

Damian

That should be:
GlobalMoneyManager.instance.pricesXML = …;
http://www.wonderwhy-er.com wonderwhy-er

Hmm… One thing that makes me uncomfortable with static class is that its probably harder to reuse and you can’t pass it into functions as argument. Here singleton is better.

P.S I wonder if you can somehow return instance when constructor is called so that instead of getting new instance you get current one

P.S.S Honestly I don’t think word “cleaner” is fitting. Code wise static class looks cleaner as there are not hassles with instance what’s so ever but Singleton is arguably a more flexible approach.

Damian

“P.S I wonder if you can somehow return instance when constructor is called so that instead of getting new instance you get current one ”

I’m not sure I understand – do you mean to only create the GlobalMoneyManager once? That’s what’s happening in the static instance getter – if GlobalMoneyManager.m_instance is not null, we just return it.

The one thing that kind of sucks about the Singleton approach though is that you can’t pass in external parameter to the GlobalMoneyManager._init() function, as it’s called in the instance getter

http://www.wonderwhy-er.com wonderwhy-er

No I mean you have this in your example:
public function GlobalMoneyManager()
{
if( !GlobalMoneyManager.m_creating )
throw new Exception( “The GlobalMoneyManager is a Singleton! Use GlobalMoneyManager.instance instead” );
}

While I would like to have:
public function GlobalMoneyManager()
{

if( !GlobalMoneyManager.m_creating )
{
return GlobalMoneyManager.instance;
}

}

So constructor returns Singleton instance instead of constructing new one or throwing and error but that’s impossible

wonderwhy-er blog

Static initializers in AS3

The problem

Static initializers in AS3

The end

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