From: "A. S. Bradbury" <asbradbury@...>
Date: 2006-09-08T22:26:20+09:00
Subject: Puzzling bug with yielded array

I have a Node class, children are stored in a hash with the node's name as the 
key and the child node object as the value. I have the method Node#each_level 
that yields each level of the node tree as an array:

    def each_level(include_self=false)
      if include_self
        node_queue=[self]
      else
        node_queue=self.children.values
      end
      yield node_queue
      while node_queue.any? {|node| node.children.empty? == false} do
        node_queue.collect! {|node| node.children.values}
        node_queue.flatten!
        yield node_queue
      end
    end

Here is the code that demonstrates the problem:

require 'ariel'

root=Ariel::Node.new :root
child1=Ariel::Node.new :child1
child2=Ariel::Node.new :child2
child1_1=Ariel::Node.new :child1_1

root.add_child child1
root.add_child child2
child1.add_child child1_1

results=[]

puts "Results when making an array then flattening it"
root.each_level do |level|
  puts "Yielded #{level.inspect}"
  puts
  raise StandardError unless level.kind_of? Array
  results << [level].flatten  # works
end

puts "results=#{results.inspect}"
puts

results=[]

puts "Results when just adding the array"
root.each_level do |level|
  puts "Yielded #{level.inspect}"
  puts
  raise StandardError unless level.kind_of? Array
  raise StandardError if level.any? {|val| val.kind_of? Array}
  results << level # doesn't work
end

puts "results=#{results.inspect}"

I'm really, really stumped. Here's the output:

> Results when making an array then flattening it
> Yielded [Ariel::Node - node_name=:child1; parent=:root;
> children=[:child1_1];, Ariel::Node - node_name=:child2; parent=:root;
> children=[];]
>
> Yielded [Ariel::Node - node_name=:child1_1; parent=:child1; children=[];]
>
> results=[[Ariel::Node - node_name=:child1; parent=:root;
> children=[:child1_1];, Ariel::Node - node_name=:child2; parent=:root;
> children=[];], [Ariel::Node - node_name=:child1_1; parent=:child1;
> children=[];]]
>
> Results when just adding the array
> Yielded [Ariel::Node - node_name=:child1; parent=:root;
> children=[:child1_1];, Ariel::Node - node_name=:child2; parent=:root;
> children=[];]
>
> Yielded [Ariel::Node - node_name=:child1_1; parent=:child1; children=[];]
>
> results=[[Ariel::Node - node_name=:child1_1; parent=:child1;
> children=[];], [Ariel::Node - node_name=:child1_1; parent=:child1;
> children=[];]]

The yielded data is always correct and the same each time, but as you can see 
the second results array is wrong. Can anyone explain what's going on here?

Alex