Proper nullable type checking in C#?

Question

Ok, my actual problem was this: I was implementing an IList<T>. When I got to CopyTo(Array array, int index), this was my solution:

void ICollection.CopyTo(Array array, int index)
{
    // Bounds checking, etc here.
    if (!(array.GetValue(0) is T))
        throw new ArgumentException("Cannot cast to this type of Array.");
    // Handle copying here.
}

This worked in my original code, and still works. But it has a small flaw, which wasn't exposed till I started building tests for it, specifically this one:

public void CopyToObjectArray()
{
    ICollection coll = (ICollection)_list;
    string[] testArray = new string[6];

    coll.CopyTo(testArray, 2);
}

Now, this test should pass. It throws the ArgumentException about not being able to cast. Why? array[0] == null. The is keyword always returns false when checking a variable that is set to null. Now, this is handy for all sorts of reasons, including avoiding null dereferences, etc. What I finally came up with for my type checking was this:

try
{
    T test = (T)array.GetValue(0);
}
catch (InvalidCastException ex)
{
    throw new ArgumentException("Cannot cast to this type of Array.", ex);
}

This isn't exactly elegant, but it works... Is there a better way though?

Answer 1

There is a method on Type specifically for this, try:

if(!typeof(T).IsAssignableFrom(array.GetElementType()))