Question

I hope this is appropriate for this site because I already figured out the answer, so it’s more a quiz than a question.

This C# code works with no problem:

WidgetRef = widget as IWidget;
WidgetRef.Init();

However if I try changing it to:

WidgetRef = (IWidget)widget;
WidgetRef.Init();

in some situations I get a “cannot cast to IWidget” exception.

At first I was dumfounded how that could be possible, because if it can’t cast in the 2nd example, it should throw a null exception in the 1st example. But I discovered it ain’t necessarily so 🙂

How is this possible?

Answer 1

OK, here’s the answer….

The incorrect assumption that I was making as that WidgetRef was a variable or field. It was actually a property, defined like this:

    private IWidget _widgetRef;
    private IWidget WidgetRef
    {
        get { return _widgetRef ?? new NullWidget(); }
        set { _widgetRef = value; }
    }

where NullWidget is a class implementing IWidget in a minimal way. So even though null was being assigned in to WidgetRef, that wasn’t what was coming out of it!