ruby - 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.

Answer 1

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.

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