Hash ordering preserved between iterations if not modified?

Question

If I iterate over a hash once, then do so again without modifying the contents, are the keys guaranteed to appear in the same order?

A quick test suggests as much:

> h = {'a' => 1, 'b' => 2, 'c' => 3}
> 100_000.times.map { h.to_s == h.to_s }.all?
=> true

Another question, if the above is allowed, can I iterate through it changing only values, without adding any new keys, and have the ordering of the keys be unchanged?

similar to this python question: Do dicts preserve iteration order if they are not modified?

Unlike the proposed duplicate I'm not interested in whether the elements have a fully specified order, only the restriction that two consecutive iterations without modification provide the same sequence.

Solution

Prior to 1.9, behavior of enumerated hashes was not in the ruby specification and therefore was up to implementation -- basically, hash enumeration behavior/pattern was undefined by the language and implementations could really do whatever they want (random? sorted? insertion order? different method every time? anything goes!)

1.9+, hash enumeration is specified by the language to be in the order of insertion, so if you know your platform is 1.9+, you can rely on it.

RubySpec