COM - How to create a method that returns a pointer to an interface?

Question

How to create a method in COM that returns a pointer to an interface, this needs to be done inside the IDL file.

EDIT:

How do I implement this within a class:

STDMETHODIMP CBlah::get_Something(IOtherBlah** retval){
return m_protectedvar->QueryInterface(retval);
}
STDMETHODIMP CBlah::put_Somthing(IOtherBlah* rhs){
m_protectedvar = rhs;
return S_OK;
}

The above is not working. I'm getting the following error:

cannot instantiate abstract class with[ Base=Blah ] due to following members:
'HRESULT IBlah::putref_Something(IOtherBlah*)' : is abstract

Answer 1

Something like this:

 interface IYourInterface {
     HRESULT GetPointer( [out, retval]IInterface** );
 };

The caller will call it like this:

 IInterface* pointer = 0;
 HRESULT hr = yourInterfacePointer->GetPointer( &pointer );

Answer 2

[ attributes here...]
interface IBlah : IDispatch {
  [id(1), propget]    HRESULT Something([out,retval] IOtherBlah** retval);
  [id(1), propputref] HRESULT Something([in] IOtherBlah* rhs);
};