MEF.txt

Glenn Block - MEF

* Can help deal with change, and also allow users to extend your app
* Not just for apps - can use it for frameworks and libraries too
  * Can allow a framework or library to evolve easily
  * Can simplify the config experience
  * Enable third parties to provide additional "value-adds"
  * Proper composition of features, etc.

* MEF consists of "Parts" - lego blocks of functionality.  Each Part provides a capability, e.g., logging., and adheres to a contract.
* Each Part imports the stuff it needs and exports the stuff it has (to expose).  Import can bring in multiple copies of something.  Supports Lazy<T>.
* The application composes - snaps together - the Parts to form the overall functionality.

* Log4Net can be composed through MEF

* Modules 
  - introduce new capabilities
  - often introduce new extensibility points
* Extensions
  - new implementations of existing capabilities
  - tend to be fine-grained
  - E.g., logger app: individual loggers, invoked through the lifecycle of the application

* Instead of shipping all the functionality in V1, just ship the hooks and let other people add the features.

* See MEFDemo code.

* Declaring MEF parts is like starting the engine of a car: gets things ready, but doesn't do anything.