NullReferenceException thrown by Microsoft.CSharp when using Generic Interfaces and Dynamic about moq4 HOT 3 CLOSED

» dynamic o = obj; var output = o.DoStuff(input);

Why make obj dynamic? If you just invoke obj.DoStuff(input) it should just
work

/kzu from mobile

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The code above is just to reproduce the issue. In the real application I'm using dynamic for implementing a multiple-dispatch pattern (visitor..), and stumbled on this error when unit testing it. I have multiple DoStuff() methods, each taking in a specialization of IInterface as its parameter. Using dynamic allows me to invoke the correct DoStuff method based on the runtime type of the IInterface object. I can post a longer sample that's closer to my application if that helps.
Thanks!!

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@AmitGee: Moq actually handles this just fine. You might have noticed that the exception does not get thrown by the mock invocation, but by the return statement in your method:

private T GenericDoStuff<T>(IInterface<T> obj, T input)
{
    dynamic o = obj;
    var output = o.DoStuff(input);
    return output; // throws NullRef
}

That is, you have received a return value from the mock, and it is stored in output. From this point onward, Moq is out of the picture.

What happens next is that the Dynamic Language Runtime cannot convert the value in output directly to type T. See what happens when you replace return output; with return (T)(object)output;, i.e. when you first "cast" from dynamic to object, and then have a regular type cast from object to T. ;-)

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