Cast received object to a List<object> or IEnumerable<object>

C# 4 will have covariant and contravariant template parameters, but until then you have to do something nongeneric like

IList collection = (IList)myObject;

You can't cast an IEnumerable<T> to a List<T>.

But you can accomplish this using LINQ:

var result = ((IEnumerable)myObject).Cast<object>().ToList();

Do you actually need more information than plain IEnumerable gives you? Just cast it to that and use foreach with it. I face exactly the same situation in some bits of Protocol Buffers, and I've found that casting to IEnumerable (or IList to access it like a list) works very well.