This version check is very simple. It checks a version number in the client code against a version number of the library (or external classes) when the main class of the library is initialized. It is also completely optional (so average users don’t need to mark up their code with version numbers).

Here’s an example:

Say you normally initialize your library using:

MyLibrary.initialize();

Which calls the initialize method:

public static function initialize():void {
   // initialize library here
}

If the external code changes unexpectedly (say through an SVN update) this could cause problems that are difficult to trace. The solution is to modify the initializer to match the client code version with the initializer version.

public static const VERSION:String = "1.6";
public static function initialize(versionCheck:String = VERSION):void {
   if (versionCheck != VERSION) {
       throw new Error ("The version check failed! This library is version " + VERSION + ". Update your code or GTFO!");
   }
   // initialize library here
}

And when you run the initializer, use the version number you’re expecting.

MyLibrary.initialize("1.6");

Some things to notice with this approach:

• I used a string instead of a number for the version number so that it would allow for sub-sub version numbers and other markers, e.g. “1.6.24 beta r545″
• Because there is a default value for versionCheck in the initializer, providing a version number is optional. Using MyLibrary.initialize() will still work and throw no errors.
• Unfortunately, there is not much you can do if the version numbers don’t match except to warn the client that the external code has changed. Still, I’ve found this to be very useful.

The code for my initializer in its entirety after the jump…

From KitchenSync.as

/**
* The current version of the library. Use this to verify that the library is the
* version that your software expects.
*/
public static const VERSION:String = "1.6";

/**
* Flag noting whether the engine has been initialized.
*/
private static var _initialized:Boolean = false;

/**
* Initializes the timing core for KitchenSync. Must be called before using any actions.
*
* @param frameRateSeed must be a DisplayObject that is added to the display list.
* @param versionCheck a string for the version you think you're using. e.g. 1.2 This is recommended
*                                         but not required. It will throw an error if you're using the wrong version of KS.
*/
public static function initialize(frameRateSeed:DisplayObject, versionCheck:String = VERSION):void
{       

	if (_initialized) {
		throw new IllegalOperationError("KitchenSync has already been initialized.");
	}
	if (versionCheck != VERSION) {
		throw new Error ("Version check failed. Please update to the correct version or to continue using this version (at your own risk) put the initialize() method inside a try{} block.");
	}

	// Initialization code omitted

	_initialized = true;
}