When a type name is not the same that the same type name

Playing with Visual Studio 2010 Beta 1 and executing this statement:

toolBar = commandBars.Add(Name:=”My toolbar”, Position:=Microsoft.VisualStudio.CommandBars.MsoBarPosition.msoBarTop, Temporary:=True)

I have encountered this funny error:

“Object must be the same type as the enum. The type passed in was ‘Microsoft.VisualStudio.CommandBars.MsoBarPosition’; the enum type was ‘Microsoft.VisualStudio.CommandBars.MsoBarPosition’.”

What I guess that the error message is trying to say is that it was expecting a parameter with the type


and it received a parameter with the type


Since the type names are the same, why is it complaining?

I recalled that this is not the first time that I see this situation. The other one was the error “[found ref ‘EnvDTE.ProjectItem’][expected ref ‘EnvDTE.ProjectItem’] Unexpected type on the stack.” when using peverify.exe.

When this happens (the expected type name and the actual type name are the same but there is an error yet), it is because the types come from assemblies that are not the same. The assemblies may even have the same name, but they were loaded from different locations, and therefore are different instances and are different “things”.

In the case of the Microsoft.VisualStudio.CommandBars.MsoBarPosition, the problem happens because .NET 4.0 introduces a new feature named “No PIA – Primary Interop Assembly” which works embedding the actual used declarations of an (ActiveX) Interop reference in the assembly being built, so that the referenced PIA assembly doesn’t need to be deployed. And it happens that the add-in wizard creates a reference to Microsoft.VisualStudio.CommandBars.dll with the “Embed Interop Types” property set to True. Once compiled, the embedded types in the add-in assembly are not the same that those in the Microsoft.VisualStudio.CommandBars.dll PIA, and it seems that the commandBars.Add method (which receives Object types as parameters) do some checks about the passed types that fail unless you set the “Embed Interop Types” property to False.

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