YOOT

Seems there is still a lot of confusion about what is Inversion of Control, what is Dependency Injection, what are the differences between the two, and how to apply one or the other properly.

Several people have reacted to a controversial post by Uncle Bob on that topic with, among the most vocal ones, Davy.

IMHO, some of the best posts on the subject that really make a clear distinction between IoC & DI are the following ones:

• Inversion of Control != Dependency Injection
• On Inversion of Control
• A small excerpt from the IoC Container doc

The whole point of IoC (forget a minute about DI) is to break the dependencies between your classes and design them as  loosely-coupled as possible (to the point that it’s actually useful of course, it’s not an engineering contest).

All the benefits that you get:

• Dependency Injection
• Better testability
• Better maintainability

are just consequences of the good design of your classes (read about SOLID also).

In the end, it’s just good Object-Oriented design, nothing more. And by good, it doesn’t mean complex, it’s actually quite simple once you got it.

Go & take the time to read those posts about the latest drop (preview 5) of MEF (Managed Extensibility Framework):

• MEF Preview 5, changes and enhancements
• Recomposition and constructors
• Poco, Mef, and custom type systems. Are you ready to take the red pill?

All of this will come for free as part of .Net 4.0 … isn’t that cool or what?

• Event Aggregation with MEF
• Adding Parallel Extensions to F#
• LINQ to NHibernate

A quick post to link Hammett's (creator of Castle Project, Windsor IoC container, and now PM on the MEF project) very interesting article about Dependencies, ownership & lifetime of components.

The MEF Team has just released its first CTP of the Managed Extensibility Framework.

This is a project to keep an eye on as it will bring Dependency Injection (and much more) right at the heart of the .Net Framework, in a new System.ComponentModel.Composition namespace (still subject to change).

The project page is here. The CTP contains some very nice demos of the early possibilities.