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Nay Pryce's Blog: "Dependency Injection" Considered Harmful

Note: This article was originally published at PHPDeveloper on 11 January 2011.
PHPDeveloper

While it's not PHP specific, this recent article from Nat Pryce talks about dependency injection and how the pattern could be considered harmful in the wrong (framework's) hands.

There are two aspects to Dependency Injection. Firstly, an object's interface should define the services that the object requires as well as those it provides. Secondly, the code that satisfies the requirements of an object by giving it a reference to the services of is collaborators is external to both the object and its collaborators. [...] The name "Dependency Injection" only relates to the second aspect. And worse, makes it sound like dependencies are "injected" through the object's encapsulation boundary rather than explicitly defined as part of the object's API.

He gives an example from the GOOS project where objects are independent and APIs are defined in such a way that any dependencies are clearly distinguished. "Code that composes objects is separate from the objects being composed".

The end goal is to need less and less code to write more and more functionality as the system grows.

Be sure to check out the comments on the post for some other good opinions and suggestions regarding dependency injection and its use in frameworks.