hash_deep_clone.rb

class Hash
  def deep_clone
    Marshal.load(Marshal.dump(self))
  end
end

h = {}                               #=> {}
a = {'a' => 1, 'b' => 2, 'c' => h}   #=> {"a"=>1, "b"=>2, "c"=>{}}
a1 = a.clone                         #=> {"a"=>1, "b"=>2, "c"=>{}}
a2 = a.deep_clone                    #=> {"a"=>1, "b"=>2, "c"=>{}}
h['foo'] = 'bar'                     #=> "bar"
a                                    #=> {"a"=>1, "b"=>2, "c"=>{"foo"=>"bar"}}
a1                                   #=> {"a"=>1, "b"=>2, "c"=>{"foo"=>"bar"}}
a2                                   #=> {"a"=>1, "b"=>2, "c"=>{}}