Book

Reality

What I expected was:

Also tested in compiled app, with same (non-crashing) behavior. Any insight? Anyone? Anyone? Bueller?

Update:

David Owens writes:

@ericasadun maybe it's debugDescription() was updated to not crash on nil? Not sure when that changed.

— David Owens II (@owensd) July 17, 2015

Sure enough:

Thanks!

And finally, word of Jordan:

@ericasadun I think the book is just being a bit imprecise. It's safe to work with the IUO (including printing), just not the value inside.

— Jordan Rose (@UINT_MIN) July 17, 2015