Bug #15834: Mutating the result of SortedSet.to_a mutates the original set, potentially violating the set's guarantees

• Status: Open
• Priority: Normal
• Assignee: knu (Akinori MUSHA)
• Target version: -
• ruby -v: ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-darwin18]
• Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN

[viko (Viko Viko)]

require 'set'

set = SortedSet[1, 2, 3]
set.to_a << -1
set.to_a << 3
set.each do |x|
  puts x
end

puts
set.add -2
set.each do |x|
  puts x
end

1
2
3
-1
3

-2
1
2
3

As can be seen, this breaks SortedSet's guarantee of ordering and Set's guarantee of uniqueness, besides being strange behaviour. Mutating the set normally undoes the changes. This bug only seems to exist for SortedSet, and not for Set itself. Workaround: dup.

[marcandre (Marc-Andre Lafortune)]

• Assignee set to knu (Akinori MUSHA)

[jeremyevans0 (Jeremy Evans)]

• File sorted-set-to_a-mutate-15834 sorted-set-to_a-mutate-15834 added

Attached is a patch with a test for fixing this.