Bug #15830: SortedSet's lazy setup causes unpredictable behaviour in subclass's initialize

• Status: Closed
• 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

require 'set'

class SortedSetWithoutLowest < SortedSet
  def initialize contents=[]
    puts "initialize, #{contents}"
    super
    lowest = to_a[0]
    puts "lowest from #{contents} is #{lowest}, removing"
    delete lowest
    puts "done initializing #{contents} to #{self}"
  end
end

3.times { SortedSetWithoutLowest[1,2,3,4,5] }

initialize, [1, 2, 3, 4, 5]
initialize, [1, 2, 3, 4, 5]
lowest from [1, 2, 3, 4, 5] is 1, removing
done initializing [1, 2, 3, 4, 5] to #<SortedSetWithoutLowest: {2, 3, 4, 5}>
lowest from [1, 2, 3, 4, 5] is 2, removing
done initializing [1, 2, 3, 4, 5] to #<SortedSetWithoutLowest: {3, 4, 5}>
initialize, [1, 2, 3, 4, 5]
lowest from [1, 2, 3, 4, 5] is 1, removing
done initializing [1, 2, 3, 4, 5] to #<SortedSetWithoutLowest: {2, 3, 4, 5}>
initialize, [1, 2, 3, 4, 5]
lowest from [1, 2, 3, 4, 5] is 1, removing
done initializing [1, 2, 3, 4, 5] to #<SortedSetWithoutLowest: {2, 3, 4, 5}>

The first such set created ends up with only [3, 4, 5], because SortedSet does some setup and then re-calls initialize (set.rb line 807). All further such sets are fine. All the sets are fine if any SortedSet has been made before, so calling SortedSet.new in the subclass's initialize and discarding the result is a viable workaround.

[jeremyevans0 (Jeremy Evans)]

• File sorted-set-initialize.patch sorted-set-initialize.patch added
• Status changed from Open to Assigned
• Assignee set to knu (Akinori MUSHA)

I agree this is a bug and the easiest way to fix it is to inline the SortedSet#initialize implementation defined by SortedSet.setup into the default implementation of SortedSet#initialize. Attached is a patch that implements that.

• Status changed from Assigned to Closed

Applied in changeset git|258843106f343d05732499dd1832958eb1bf64f0.

---

Fix SortedSet subclasses that override initialize

The first time SortedSet#initialize is called, it overwrites
itself, then recalls #initialize, which results in calling the
subclass's initialize, not the current initialize.

Just inline the default initialize behavior to avoid this issue.

No test for this as it can only be triggered the very first time
that SortedSet#initialize is called.

Fixes [Bug #15830]