Reflecting Type Equivalence

Today, I want to write about another of the new features in .NET 4: Type Equivalence and Embedded Interop Types. This feature allows you to embed type references to interop types in your assembly. In the end, this allows you to avoid deploying interop assemblies.

Anyway, I don't want to go into much detail about this. You can read more about it here Type Equivalence and Embedded Interop Types and here Walkthrough: Embedding Types from Managed Assemblies

What I want to do here is show you how the types get placed in the assembly. This is pretty much just a quick look with reflector in an assembly with embedded COM types.

So here's what I've done to test this:

I've created a simple project, added a reference to MSXML, then in the added reference properties, I've made sure the property "Embed Interop Types" was set to "True" (This is what defines if a reference is to be embedded).

Then I've inserted this small code snippet to use this library:

Note that in the code above I have a comment with the code that I would regular use to create an instance of the DOMDocument class. However you can't use code like this if you wish to use type equivalence. Classes aren't embedded, interfaces are. If you try to use that line of code you'll get the compilation error below.

Now, let's finally look at the compiled assembly with the .NET developer's favorite tool: Reflector.

As you can see above, a small part of the MSXML2 Namespace as been included in our brand new assembly. Note that only the referenced interfaces (along with its own dependencies) by our code were included in the assembly, so this means that not only you avoid redistributing an interop, but you also end up reducing the size of your application dependencies!