Within minutes of posting a link to Code Blog, someone submitted the following solution...
public IList Sort(IList list)
{
((ArrayList)list).Sort();
return list;
}
This is certainly the simplest possible solution to the problem (in true XP style). But in my tests I didn't intend this to work! In fact at one point I was passing an array of doubles (which implements IList) to stop this kind of 'cheating'. Unfortunately passing an array is open to a similar kind of abuse.
What is the easiest way to restrict the casting of an object? I've revised the tests to use a class called RestrictedTypeProxy. I am using it as follows to restrict the interface my ArrayList object is exposing...
ArrayList arrayList = new ArrayList();
RestrictedTypeProxy proxy = new RestrictedTypeProxy(arrayList, typeof(IList));
IList list = (IList)proxy.GetTransparentProxy();
You can also pass any number of MarshalByRefObjects or interfaces. For example...
RestrictedTypeProxy proxy = new RestrictedTypeProxy(myOb, typeof(MBRO), typeof(IList), typeof(IDisposable));
You can see how it's implemented by scrolling to the bottom of the page here (oops, not any more). I will need to use permalinks for historic challenges. If you still want to see the code, it looks like Fabrice has found a way!