Dual enumerators, second one via interface- type collisions on implementation

Question

I have a generic class that implements IList

public class ListBase<T>: IList<T>, IListBase{

   IEnumerator<T> GetEnumerator(){ ....
   System.Collections.IEnumerator GetEnumerator(){ return GetEnumerator();}

}

The IListBase is an interface I use to access methods on this class for cases where I don't know the type of T at runtime.

I need to implement a second Enumerator via this IListBase interface which will iterate the members of my class and return them cast as a base type that all members will implement.

I've tried having the IListBase implement my specific Enumerator:

public interface IListBase: IEnumerable<MemberBaseType> { ....

But this blows up due to the fact that T and MemberBaseType could be the same in some instances. Even adding the enumerator members to the interface and then using explicit declarations doesnt help this problem.

I then tried adding another method to call for just getting specific IEnumerator, but the compiler then complains about not finding a public GetEnumerator method to use with this type...

Any recommendations for adding this secondary enumerator so they don't collide with each other?

Answer 1

Having two enumerators at the same level that do different things is (IMO) a bad idea. You can probably force it, but as soon as someone casts your type (especially if casting to the non-generic interface) it is largely guesswork which they will get.

I would recommend (instead) making this available via a property, for example .Members, where .Members offers this enumeration. Then no ambiguity of intent, and no compiler unhappiness. So I could use:

foreach(var member in list.Members) { /* add columns */ }
foreach(var item in list) { /* add rows */ }

You might also consider ITypedList, which may have some relevence here, especially if you want to data-bind to your list (this isn't necessary if T by itself defines everything cleanly).

In short:

public interface IListBase {
    IEnumerable<MemberBaseType> Members {get;}
}