#module MyHashExtension
class Hash
  alias_method :old, :[]=
  def []=( key, val )
    #super( key, val )
    self.old(key,val)
    if @keys and !@keys.include?(key) then
      @keys << key
    end
  end
  def each
    @keys = self.keys
    @keys.each do |k|
      yield k, self[k] if self.has_key? k
    end
    @keys = nil
  end
  alias :each_pair :each
  def each_key
    @keys = self.keys
    @keys.each do |k|
      yield k if self.has_key? k
    end
    @keys = nil
  end
end

if __FILE__ == $0
# usage: ruby1.9 -I . -rmod_hash test.rb
# or:    require 'mod_hash' before using Hash

h = Hash.new
#h = {}.extend MyHashExtension
h[1] = 2

h.each do |k,v|
  h[k+1] = v*2 if v < 10000000000
  $stdout << "#{k}: #{v}\n"
end
p h
end