Bug #14069: Document order of elements in Set

• Status: Rejected
• Assignee: knu (Akinori MUSHA)
• Target version: -
• ruby -v: 2.4
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN

[abotalov (Andrei Botalov)]

Hash enumerates values in the insertion order.

Set is built on Hash so it does the same.
However, this is currently believed to be a not documented implementation detail. See:
https://stackoverflow.com/a/14468621/841064
https://stackoverflow.com/questions/10361250/does-set-in-ruby-always-preserve-insertion-order#comment13351258_10361275
https://spin.atomicobject.com/2012/09/04/when-is-a-set-better-than-an-array-in-ruby/

I think it would be better to explicitly document that Set class enumerates keys in the insertion order.

[jwmittag (Jörg W Mittag)]

Is that actually guaranteed by the specification? Can you point to any specification or documentation or official statement by the core team that supports your assertion that sets are insertion-ordered?

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Assigned
• Assignee set to knu (Akinori MUSHA)

I believe the fact that sets are currently insertion ordered due to the use of hash is an implementation detail, and we shouldn't document it.

[jeremyevans0 (Jeremy Evans)]

• Status changed from Assigned to Rejected