Question

I am trying to determine if an object x is a list. It may be a list of any type and with any generic parameter.

If it is, then I want to iterate over it if it is. This is the best I could come up with, but it fails due to a compilation error

if(x is List){
    foreach(Object o in (List)x){
        ;
    }
}

How can I do this?

Answer 1

The easiest way is to cast to IList. This is a non-generic interface and could be implemented by non-generic lists (such as ArrayList) but I’m guessing that won’t be a concern for you:

if (x is IList) {
  foreach (object o in (IList)x) {
    // ...
  }
}

(And if all you need to do is foreach, you don’t even need IList: IEnumerable will suffice.)

Note that the non-generic IList and IEnumerable are in the System.Collections namespace, which is not using-ed by default. So you will need to add using System.Collections; (thanks to Reed Copsey for noting this).