I think the Date class is an unfortunate example to use, its too prone to being confused with the idea of a timeline of mutable state. Maybe a better example to

I think the Date class is an unfortunate example to use, its too prone to being confused with the idea of a timeline of mutable state. Maybe a better example to use would be the concept of a document, and that parts of it don't change while you're reading it. On the other hand, his audience will always be familiar with the Date class... I've been following Rich's work for a while and I felt myself almost slip into confusion.