ruby Ordered-hash, add method to a eigen-class

orderedhash.rb

hash={}

hash.instance_eval do   # if you want this for all hashes, replace this line with class Hash
  def []=(key,val)
    ordered_keys << key
    super(key,val)
  end

  def ordered_keys
    @ordered_keys ||= []
  end

  def delete(key)
    ordered_keys.delete(key)
    super(key)
  end

  def each_in_order(&block)
    ordered_keys.each do |key|
      yield(key, self[key])
    end
  end
end


hash['january'] = 'foo'
hash['february'] = 'bar'
hash['march'] = 'meow'

puts hash.ordered_keys.inspect
puts hash.inspect

hash.delete('february')
puts "deleted feb"
puts hash.ordered_keys.inspect
puts hash.inspect

hash.each_in_order do |key, val|
  puts "key: #{key} val: #{val}"
end

output.txt

["january", "february", "march"]
{"january"=>"foo", "february"=>"bar", "march"=>"meow"}
deleted feb
["january", "march"]
{"january"=>"foo", "march"=>"meow"}
key: january val: foo
key: march val: meow