Part 1. Putting Dependency Injection on the map

Dependency Injection (DI) is one of the most misunderstood concepts of object-oriented programming. The confusion is abundant and spans terminology, purpose, and mechanics. Should it be called Dependency Injection, Inversion of Control, or even Third-Party Connect? Is the purpose of DI only to support unit testing or is there a broader purpose? Is DI the same as Service Location? Is a DI CONTAINER required?

There are plenty of blog posts, magazine articles, conference presentations, and so on that discuss DI, but, unfortunately, many of them use conflicting terminology or give bad advice. This is true across the board, and even big and influential actors like Microsoft add to the confusion.

It doesn’t have to be this way. In this book I present and use a consistent terminology that I hope others will adopt. For the most part, I’ve adopted and clarified existing terminology defined by others, but occasionally I add a bit of terminology where none existed previously. This has helped me tremendously in evolving a specification of the scope or boundaries of DI.