Nested collection comparison

[darkleaf]

(compare [1] [2]) ;; -1 is ok because vecotors are Comparable.
(compare '(1) '(2)) ;; BOOM throws an exception because lists are not Comparable, it's expected.
(compare ['(1)] ['(2)]) ;; BOOM it is also expected.

(db/value-compare [1] [2]) ;; -1
(db/value-compare '(1) '(2)) ;; -22.. it works because lists are compared by hash
(db/value-compare ['(1)] ['(2)]) ;; BOOM This case is too strange, I can compare vectors and lists but I can't compare vectors of lists.

I can wrap my vectors in a hash-map or a list and it works: (db/value-compare {:value ['(1)]} {:value ['(2)]}). But it's a hack.

Should we provide our own Compare protocol with hash support? In this case, we have to repeat a .compareTo method for all collections. It looks like .compareTo but calls our value-compare instead of Util/compare https://github.com/clojure/clojure/blob/c1ede7899d8d7dd4dcd6072d5c0f072b9b2be391/src/jvm/clojure/lang/APersistentVector.java#L439

This issue has a low priority.

[tonsky]

Total compare function is great, but re-implementing it for every Clojure and Java type might be too much? On the other hand, maybe there’s not much work, in that case we can go for this.

[tonsky]

Another solution might come from the user, who might decide not to store vectors of arbitrary types?

[darkleaf]

And one more question. How do you think about comparing objects by their hash?
Two different objects can have equal hashes. It just works because we haven't a better solution, doesn't it?

[tonsky]

It just works because we haven't a better solution, doesn't it?

Yes. Maybe identityHashCode would be better, if it’s based on object pointers addresses (needs checking)?