The misleading MIDL error message: MIDL5023: The arguments to the parameterized interface are not valid

Raymond Chen

Raymond

Suppose you’re writing an IDL file for the Windows Runtime. You have a method that returns a vector view of strings, but for some reason the compiler tells you that “The arguments to the parameterized interface are not valid.”

runtimeclass Widget
{
  Windows.Foudation.Collections.IVectorView<String> GetNames();
}

The argument to the parameterized interface is String, and that’s certainly a valid argument for IVector­View, isn’t it?

Yes, it’s a perfectly fine argument for IVector­View.

But what you have there isn’t the IVector­View you think you have.

  Windows.Foudation.Collections.IVectorView<String> GetNames();

You misspelled Foundation.

The compiler is technically correct: String is not a valid argument for the parameterized interface Windows.Foudation.Collections.IVectorView. But that’s because there are no possible valid arguments for the parameterized interface Windows.Foudation.Collections.IVectorView, because Windows.Foudation.Collections.IVectorView is not a legal parameterized interface!

The order in which the compiler checks for validity happens to result in a misleading error message, making you believe that the error is in the argument, when in fact the error is in the interface.

Bonus chatter: You can avoid some of the risk of typos by taking advantage of the shorthand notation that lets you omit Windows.Foundation.Collections:

runtimeclass Widget
{
  IVectorView<String> GetNames();
}

Of course, you can still get the misleading error message if you typo IVectorView as, say, IVetorView. So the problem is still there. The shorthand just makes it a little bit less likely.

1 comment

Comments are closed. Login to edit/delete your existing comments