In his past few posts Paul Jones has been looking at dependency injection versus service locators. In this new post he continues on the topic comparing three methods for working with objects - factories, registries and service locators.
In last week’s episode of this unexpected series, I said, “Go ahead and use Service Locator, but make sure each Locator contains only one type of object. This condition of restraint will keep a single locator from becoming a menace.” [...] The “only one type of object” constraint generated some discussion regarding factories and registries. [...] The differences between factories, registries, and containers (both service locators and dependency injection containers) can be subtle and hard to grasp at first. Here’s how I keep them straight.
He breaks them down with a simple definition for each related to how the object is created and its intended purpose. He also includes an example of a service locator he's created and a snippet of example code showing it in use.
Again, I must stress: Service locators can easily get out of control. If you can avoid using a service locator, you should.