hashdoubly.rb

class HashDoubly
  attr_accessor :key, :value
  
  def initialize hash=nil
    if hash
      @key = hash.dup
      @value = hash.dup.invert
    else
      @key = {}
      @value = {}
    end
  end
end

hd = HashDoubly.new({
  1 => "foo",
  2 => "bar",
  3 => "baz",
})

p hd.key[2] #=> "foo"
p hd.value["foo"] #=> 2