This is true in general. Both the DI and SL patterns provide containers that you pull objects out of. However, the essential difference between them is that your application code is aware of the Service Locator pattern, but Dependency Injection is invisible to the app.

So, if you take your DI container and pass it to a constructor, you are really using the DI container in a Service Locator manner. The key question to ask is: If you were to change the interface to the DI container, does your app need to change as well.

Someone else asked me how to decide between DI and SL, or just rolling your own. My answer is to look at the amount of pain you suffer on configuring your the modules[1] of your system. Ruby is flexible enough so that most projects can get by without either DI or SL. When it begins to get cumbersome managing different configurations by hand, it is fairly painless to switch to lightweight DI container such as Needle.

Note 1:

By "configuring your modules", I don’t mean supplying configuration data to your program, but deciding what modules should be selected. For example, while testing you might want to use a mock database layer instead of the real thing.

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