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Will Rails Discover Dependency Injection?

Few are as keen to emphasize their perceived superiority as Rails developers. Don't get me wrong, it's a solid marketing strategy. What's problematic is when you succumb to it to the extent that you see the rest of the world as mere copycats without a chance to ever catch up. But the world isn't like that.

Take Dependency Injection, for example. While people in the PHP and JavaScript communities discovered DI later, Ruby on Rails remains untouched by it. I was puzzled why a framework with such a progressive image was lagging behind, and after some digging, I found an answer from various sources on Google and karmiq, which states:

Ruby is such a good language that it doesn't need Dependency Injection.

This fascinating argument, moreover, is self-affirming in an elitist environment. But is it really true? Or is it just blindness caused by pride, the same blindness that recently led to much-discussed security vulnerabilities in Rails?

I wondered if perhaps I knew so little about Ruby that I missed some key aspect, and that it truly is a language that doesn’t need DI. However, the primary purpose of Dependency Injection is to clearly pass dependencies so that the code is understandable and predictable (and thus better testable). But when I look at the Rails documentation on the “blog in a few minutes” tutorial, I see something like:

def index
  @posts = Post.all

Here, to obtain blog posts, they use the static method Post.all, which retrieves a list of articles from somewhere (!). From a database? From a file? Conjured up? I don’t know because DI isn’t used here. Instead, it’s some kind of static hell. Ruby is undoubtedly a clever language, but it doesn’t replace DI.

In Ruby, you can override methods at runtime (Monkey patch; similar to JavaScript), which is a form of Inversion of Control (IoC) that allows for substituting a different implementation of the static method Post.all for testing purposes. However, this does not replace DI, and it certainly doesn't make the code clearer, rather the opposite.

Incidentally, I was also struck by the Post class in that it represents both a single blog post and functions as a repository (the all method), which violates the Single Responsibility Principle to the letter.

The justification often cited for why Ruby doesn't need DI refers to the article LEGOs, Play-Doh, and Programming. I read it thoroughly, noting how the author occasionally confuses “DI” with a “DI framework” (akin to confusing “Ruby” with “Ruby on Rails”) and ultimately found that it doesn’t conclude that Ruby doesn’t need Dependency Injection. It says that it doesn’t need DI frameworks like those known from Java.

One misinterpreted conclusion, if flattering, can completely bewilder a huge group of intelligent people. After all, the myth that spinach contains an extraordinary amount of iron has been persistent since 1870.

Ruby is a very interesting language, and like in any other, it pays to use DI. There are even DI frameworks available for it. Rails is an intriguing framework that has yet to discover DI. When it does, it will be a major topic for some of its future versions.

(After attempting to discuss DI with Karmiq, whom I consider the most intelligent Railist, I am keeping the comments closed, apologies.)

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