Dependency Injection in Xyster

Posted by Double Compile on Monday, December 10. 2007 in Xyster

Inversion of Control is one of those design patterns that once you "get it", you'll start seeing that it can be applied basically all over the place. It's the lesson of "tell; don't ask".

I've spent a good deal of time this weekend with the Xyster incubator; creating a Dependency Injection package called Xyster_Container based almost entirely on PicoContainer. The good: PHP method signatures are much more simple than Java's; only one constructor per class. The bad: PHP scalar method parameters are not typed, so you cannot use ReflectionParameter::getClass() on them. This first release won't support the LifeCycle capabilities or annotations, but at least annotations support is planned (remember, it's still in the incubator).

This Dependency Injection package will be used to replace/redo the Xyster_Application package. You'll read in Fowler's article (linked above) about the Service Locater concept, which was what Xyster_Application was intended to be. While the Locater might still be done, I think it's more important that application services can be injected into the classes that use them.

For now, read up on Dependency Injection. You'll wonder where it's been all your life.

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