COM - use IEnumerable in ATL C++ project

Question

I use in my C++ COM server a C# COM DLL that implements IEnumerable for iterating over a collection.

1. How do I specify in my native code that I want to access IEnumerable -> GetEnumerator() method from the instance object of C# Dll ? Do I have to import some *.tlb in order to see IEnumerable interface in my C++ project ? Ienumerable interface I saw is defined by mscorelib.dll

2. Can I further expose an IEnumerable interface to my clients (defined in IDL in my C+ project). An example would be helpful

Answer 1

It is automatically translated by the type library exporter, System.Collections.IEnumerator is [ComVisible] and gets translated to IEnumVARIANT. For example:

using System;
using System.Collections;
using System.Runtime.InteropServices;

[ComVisible(true), InterfaceType(ComInterfaceType.InterfaceIsDual)]
public interface IExample {
    IEnumerator GetEnumerator();

}
[ComVisible(true), ClassInterface(ClassInterfaceType.None)]
public class Example : IExample {
    public IEnumerator GetEnumerator() {
        yield return 42;
    }
}

Gets translated to this type library fragment:

// TLib :     // TLib : mscorlib.dll : {BED7F4EA-1A96-11D2-8F08-00A0C9A6186D}
importlib("mscorlib.tlb");
// TLib : OLE Automation : {00020430-0000-0000-C000-000000000046}
importlib("stdole2.tlb");

// Forward declare all types defined in this typelib
interface IExample;

[
  odl,
  uuid(9B046FDE-9234-3DE7-B055-DADE8F7B4A99),
  version(1.0),
  dual,
  oleautomation,
  custom(0F21F359-AB84-41E8-9A78-36D110E6D2F9, "IExample")    

]
interface IExample : IDispatch {
    [id(0xfffffffc)]
    HRESULT GetEnumerator([out, retval] IEnumVARIANT** pRetVal);
};

Note the importlib directive for mscorlib.tlb, present in c:\windows\microsoft.net\framework\v2.0.50727 and found by the compiler without help.