Ruby 1.9.2 vs 1.9.3, gotcha with Struct.new and constant scope

connection.rb

# Define a simple class with a DEBUG constant
#
Connection = Struct.new(:name, :state) do
  DEBUG = false
  def self.debug?
    DEBUG
  end
end

# A quick sanity check
Connection.debug?
=> false

connection1-riddle.rb

# Let's now change the constant from false to true
Connection::DEBUG = true

# ruby 1.9.2-p180
Connection.debug?
=> true

# ruby 1.9.3-p0
Connection.debug?
=> false

connection2-actual.rb

DEBUG = false
Connection = Struct.new(:name, :state) do
  def self.debug?
    DEBUG
  end
end

connection3-explained.rb

# ruby 1.9.2-p180
Connection::DEBUG = true # Actually does DEBUG=true
Connection.debug?        # Reads new value of DEBUG
=> true

# ruby 1.9.3-p0
Connection::DEBUG = true # Creates new constant Connection::DEBUG
Connection.debug?        # Reads unchanged value of DEBUG
=> false

connection4-alt.rb

Connection = Struct.new(:name, :state) do
  def self.debug?
    Connection::DEBUG
  end
end
Connection::DEBUG = false

connection5-alt.rb

class Connection
  DEBUG = false
  
  attr_accessor :name
  attr_accessor :state
  
  def init(name, state)
    @name = name
    @state = state
  end
  
  def self.debug?
    DEBUG
  end
end

Read the blog post for a detailed explanation of this Gist: http://blog.55minutes.com/post/16472600410/trivia-constants-in-ruby-1-9-2-vs-1-9-3