Comment by limit499karma

> where the keys might be complex compound objects

Given that any (simple) object has a unique c.a. identity, even anonymous (and unordered) containment in the parent object provides a key, that is k->k, with implicit order over {K} in the domain of keys (say ascending sort on k0..kn). As you obviously know, there are various schemas for that, such as "objspace://oid/<value-hash>". By definition, that is a bounded domain, with the same cardinality as the hash space. So then there remains the matter of nesting (aka trees) in which case unique identity of the parent is recursively computed as we walk up the tree from the leaves.