Why use MEF metadata instead of just extending the interface to include the metadata?

So intead of using ExportMetadata attribute, why not just extend the interface inst开发者_如何转开发ead?

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if you import Lazy<> stuff via MEF you can look into the metadata without instantiate your object.

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Good question. I think that extending the interface is the correct thing to do whenever you have the option. It much better communicates intent.

However, we may need more fine-grained control over interfaces that we don't own. In those cases we can use ExportMetadata as a substitute.

In my opinion you should only use ExportMetadata when there is no other option available to you.