For example, attempting to use a class with just one stored property of an enum type that can't be represented in Objective-C will crash. It crashes in realizeClass when doing ivar offset stuff I believe (after turning on the debug logging for this).
Partial stack trace:
#0 0x0000000180d388e4 in realizeClass(objc_class*) ()
#1 0x0000000180d365ac in _class_getNonMetaClass ()
#2 0x0000000180d3b8b4 in lookUpImpOrForward ()
#3 0x0000000180d45d78 in _objc_msgSend_uncached_impcache ()
#4 0x00000001000cd958 in type metadata accessor for BadClass ()