interface Identity

pub interface Identity :: [Hashable]

Conforms to Hashable.

Compares an object by itself and hashes it by where it lives.

class Node :: [Identity] is given an equals that is same(this, o) and a hash of its address, so a Map<Node, X> keys by the object without a member written. Only a class can conform; a value has no identity. Nothing on the heap moves, so an object keeps its address while it lives.