Error in question N4, chapter What Is Ownership? (4.1)

[Wirpple]

Incorrect solution. If we reproduce all four options in the IDE from the question, they will all produce undefined behavior. However, for some reason, only three of the four are mentioned in the question, which may mislead the reader.

[seancwall]

I was also confused a bit by this question. As Wirpple pointed out, the compiler rejects all the snippets given, but I think the intent of the question is not "which do not compile" but strictly "which aren't safe". Technically, the one example they left out isn't strictly unsafe, as the heap memory pointed at by 'b' hasn't been deallocated yet, so you could dereference the memory pointed at by b. But, the Rust compiler will still reject it. I think this is a very subtle point which isn't made clear by the question.