In v1 of MEF, we focused on getting the default programming model super easy to use (most MEF users need to only understand a handful of types) and getting the ComposablePart abstractions right (making it possible to create custom programming models). We did not focus on making it easy to create custom programming models (quite advanced scenario).

Here is the talk summary:

Learn about guidelines that have helped the Microsoft .NET Framework grow into the most popular developer framework Microsoft has ever created. After ten years of use, we have an enormous amount of real customer data about what makes great framework design. Whether you are building your own framework or just want to get the most out of the .NET Framework, this is a must-attend talk! Join Krzysztof Cwalina and Brad Abrams, authors of the Dr. Dobbs award winning "Framework Design Guidelines" book, and get a sneak peek at the content from the 2nd edition (first available at PDC2008).

In the first one, we are talking about our PDC presentation (for those at the PDC, it’s at 4pm today). You can get it at 10 Years of Framework Design Guidelines (video).

The second interview is about just released 2^nd edition of the Framework Design Guidelines book. You can get the video at Framework Design Guidelines: Conventions, Idioms, and Patterns for Reusable .NET Libraries (video)

Enjoy!

We have just released an update to MEF. You can get it at http://www.codeplex.com/MEF

The changes are quite significant:

1.       The preview ships with sources under a very permissive license (Ms-LPL).

2.       We now support constructor injection. Feature that the community asked for.

3.       We completely redesigned MEF’s extensibility points. The extensibility points are designed to support writing custom providers of composition data. For example, out of the box MEF requires composable parts to be attributed with attributes that provide metadata describing the composition. We got lots of feedback that this is not acceptable in many scenarios. The new extensibility points make it easier to extend MEF to externalize the metadata (to an XML file for example). Note, that the changes are just the first step toward the goal of making the extensibility easy and powerful. We will most probably keep making improvements in this space in the future, so feedback on the new extensibility points would be more then welcome.

4.       We significantly cleaned up the container APIs. But as above, there is more clean up to come in the future.

The current release has just a few extensibility points, but you should expect more in the future. 

KRZYSZTOF CWALINA One of the biggest misconceptions about exceptions is that they are for “exceptional conditions.” The reality is that they are for communicating error conditions. From a framework design perspective, there is no such thing as an “exceptional condition”. Whether a condition is exceptional or not depends on the context of usage, --- but reusable libraries rarely know how they will be used. For example, OutOfMemoryException might be exceptional for a simple data entry application; it’s not so exceptional for applications doing their own memory management (e.g. SQL server). In other words, one man’s exceptional condition is another man’s chronic condition.