What are alternatives to generic collections for COM Interop?

I am attempting to return a collection of departments from a .NET assembly to be consumed by ASP via COM Interop. Using .NET I would just return a generic collection, e.g. List<Department>, but it seems that generics don't work well with COM Interop. So, what are my options?

I would like to both iterate over the list and be able to access an item by index. Should I inherit from List<Department>, implement an IList, IList<Department> or another interface, or is there a better way? Ideally I would prefer not to have to implement a custom collection for every type of list I need. Also, will List[index] even work with COM Interop?

Thanks, Mike

Example .NET components (C#):

public class Department {
    public string Code { get; private set; }
    public string Name { get; private set; }
    // ...
}

public class MyLibrary {
    public List<Department> GetDepartments() {
        // return a list of Departments from the database
    }
}

Example ASP code:

<%
Function PrintDepartments(departments)
    Dim department
    For Each department In departments
        Response.Write(department.Code & ": " & department.Name & "<br />")
    Next
End Function

Dim myLibrary, departments
Set myLibrary = Server.CreateObject("MyAssembly.MyLibrary")
Set departments = myLibrary.GetDepartments()
%>
<h1>Departments</h1>
<% Call PrintDepartments(departments) %>
<h1>The third department</h1>
<%= departments(2).Name %>

Related questions:

• Using Generic lists on serviced component
• Are non-generic collections in .NET obsolete?

From stackoverflow

• After some more research and trial-and-error, I think I found a solution by using System.Collections.ArrayList. However, this does not work with getting a value by index. To do so, I created a new class ComArrayList that inherits from ArrayList and adds new methods GetByIndex and SetByIndex.

  COM Interop compatible collection:

  public class ComArrayList : System.Collections.ArrayList {
      public virtual object GetByIndex(int index) {
          return base[index];
      }
  
      public virtual void SetByIndex(int index, object value) {
          base[index] = value;
      }
  }
  

  Updated .NET component MyLibrary.GetDepartments:

  public ComArrayList GetDepartments() {
      // return a list of Departments from the database
  }
  

  Updated ASP:

  <h1>The third department</h1>
  <%= departments.GetByIndex(2).Name %>
  

• Since you are only consuming the data in ASP, I would suggest returning Department[]. This should map directly to a SAFEARRAY in COM. It supports enumeration and indexed access too.

  public Department[] GetDepartments() {
      var departments = new List<Department>();
      // populate list from database
      return departments.ToArray();
  }