In his latest post Ralph Schindler takes another look at the usefulness of Dependency Injection Containers and whether or not they're the right thing to use for your situation.

To DiC, or not to DiC: that has seemed to be the question in PHP for the last few years. Most people generally agree that injecting dependencies is the right thing to do. For those writing a framework, or any shared codebase where extensibility or the ability to grow the codebase is a core philosophical tenet, not injecting dependencies is doing a disservice to the project in the long run. So, as I've stated before, the question becomes how do we manage the added complexity that comes with practicing dependency injection?

He briefly covers two topics that are often confused - the concepts of a service locator and a true dependency injection container. He then talks about the more correct situations to use each of them, mentioning a few questions you can ask about your app to determine the best fit. To illustrate, he includes a simple example where he mixed the two - DIC for models and service location for the controllers.

PHPMaster.com has posted the second part of Alejandro Gervasio's series looking at dependency injection, service locators and factories. In this new part of the series, he picks back up with his look at these patterns and how they can reduce your dependencies on things like "new" even more.

While it's fair to admit that factories do have a neat niche in a number of special use cases, I'm not so merciless as to condemn Service Locators and plain Dependency Injection to an unfair exile. In this final part we'll take a closer look at the implementation of these popular patterns so that you can pick up the one that best suits the need at hand.

He talks some about "class collaborators" as used in service locators and using it in his FileStorage example to find and use pre-created objects. He compares this method with a more simple dependency injection approach, noting that not only is it simpler to maintain but also can cause less overhead required for the DIC.

In a new post to his blog, Chris Hartjes shares one thing that you can use to make your code easier to test - using a dependency injection container and how it compares to a service locator.

People often ask me what's the one thing they could do for their code base RIGHT NOW that will make it easier to test. To me, the answer is simple: make sure you are using Dependency Injection (yes the link is long and has code samples in Java, but whatever). Without the ability to "inject" your dependencies into your code (whether it is class methods or functions) you will have problems testing modules of code in isolation from each other.

He shows the possible uses of DICs, including code samples, and talks the differences between the two. He explains that the real difference in them is how its being used. When it's used to add and remove instances, it's a container. When its actually put to use and passed into a class, it morphs into a service locator.