Your code stops compiling with a pretty unhelpful error message. Y'know, like Segmentation Fault 11, and a stack trace into the swift compiler sourcecode if you

Your code stops compiling with a pretty unhelpful error message. Y'know, like Segmentation Fault 11, and a stack trace into the swift compiler sourcecode if you're lucky. XCode doesn't always crash (though it does, frequently), but syntax highlighting goes away at the first hint of an issue.