Dependency Injection (DI)

What is it?

• "A 25-dollar term for a 5-cent concept" - James Shore
• Technique whereby the dependencies of an object are provided to it, rather than the constructing them or accessing them through another object.

Cool, cool, cool. And what's a dependency, again?

• When object A requires (depends on) the presence or functionality of object B, object B is a dependency of object A.

Alright, so why should I care?

• Primary gain is making testing easier.
• Encourages loose coupling.
• Puts an object's dependencies front and center, easier to see.
• Changes to the application are (potentially) easier. Fewer breaking code changes.

What's the catch?

• It can be hard to understand sometimes.
• Dependency injection isn't always mature in all languages/frameworks.