[Pitch] Noncopyable (or "move-only") structs and enums

[Joe_Groff]

@John_McCall

It would be, yes. It really comes down to whether we have to do something else with the value after calling the accessor, and the calls set and _modify always come at the end of their respective sequences. I think consuming willSet is the only one that I think needs to just be straight-up impossible because it’s never at the end. My bigger concern is about consuming get — we might have to require a _modify to make a property like that mutable, because otherwise we will have no way to do a read-modify operation.

Good point, thanks for bringing that up. Another possibility for a noncopyable property is that you might want all three of consuming get, [borrowing] read, and [mutating] modify in order to support forwarding in all of consuming, borrowing, and modifying cases. This proposal doesn't yet try to formalize the read and modify coroutines, so I think for now we should say that you can't have a set with a consuming get.