Perhaps I'm misapplying Unity, but here goes. I have a couple of applications, both of which load the same plugin assemblies. All assemblies require a library, and I want them to be able to access this library via Unity. However, in order to use Unity, or any other IoC framework, I'd have to write an interface for this library. I will probably do this, but since an interface isn't really needed for anything other than to support Unity, I am afraid that this means that I am 1) missing the point, or 2) misapplying the framework. If I avoid something that offers me DI, then I'd have to make the library class a singleton, and then pass it to all of the plugin constructors, or via a public property, and I don't want to do this.

That said, and without actually implementing anything with Unity yet, I'm not getting one other detail -- although Unity will let me request the library via Resolve<>, my plugins will still need to have a reference to the Unity instance that is created in the main applications. So is this a case where your only option is to pass the Unity reference to all of the plugins, but then it's convenient from that point on, merely because you can use Unity to get at all of the other dependencies?