Question

I’m trying to introduce dependency injection (DI) as a pattern here at work and one of our lead developers would like to know: What, if any, are the downsides to using the dependency injection pattern?

Note I’m looking here for an, if possible, exhaustive list, not a subjective discussion on the topic.

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Clarification: I’m talking about the dependency injection pattern (see this article by Martin Fowler), not a specific framework, whether XML-based (such as Spring) or code-based (such as Guice), or "self-rolled".

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Some great further discussion / ranting / debate is going on the Reddit’s subreddit /r/programming.

Answer 1

A couple of points:

• DI increases complexity, usually by increasing the number of classes since responsibilities are separated more, which is not always beneficial
• Your code will be (somewhat) coupled to the dependency injection framework you use (or more generally how you decide to implement the DI pattern)
• DI containers or approaches that perform type resolving generally incur a slight runtime penalty (very negligible, but it’s there)

Generally, the benefit of decoupling makes each task simpler to read and understand, but increases the complexity of orchestrating the more complex tasks.