Casting a generic collection to base type

Question

I\'ve got an IList that I want to cast to ICollection but when I attempt an explicit cast, I get null

Answer 1

I don't think it's possible, and indeed it shouldn't be:

class BaseClass {}
class DerivedClass : BaseClass {}
class OtherClass : BaseClass {}

void test()
{
  List list = new List();
  slice(list); //you want to do this
}

void slice(IList list)
{
  //yikes! adding OtherClass to List
  list.Add(new OtherClass());
}