Feature #16992: Sets: officially ordered

• Status: Assigned
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[marcandre (Marc-Andre Lafortune)]

Officially, set elements have uncertain order. This predades when Hash started being ordered (Ruby 1.9.0, Xmas 2007). Sets have since been de-facto insertion-ordered. FYI, in those 13 years, there have been about 70 commits to lib/set.rb.

I have the impression that a non-negligible amount of code in the wild rely on sets being ordered, at least under most circumstances. I feel that this should be officialized.

If sets are truly unordered, then why do we hesitate to make an optimization of & and |: https://bugs.ruby-lang.org/issues/15281

See also: https://bugs.ruby-lang.org/issues/14069

[marcandre (Marc-Andre Lafortune)]

• Related to Feature #16989: Sets: need ♥️ added

[Eregon (Benoit Daloze)]

+1 from me. Hash if officially ordered.
Making Set unordered would likely break many things.
In practice I would think many Set usages already assume it ordered.
Similar to what I said in https://bugs.ruby-lang.org/issues/15281#note-9

Having unordered elements does not feel Ruby-like, it introduces non-determinism in things as simple as #each.

If super high performance is wanted and being unordered helps, then using a separate class or external gem for that makes sense I think.

[hsbt (Hiroshi SHIBATA)]

• Status changed from Open to Assigned