rubyでハッシュのキーを再帰的にシンボルに変換する

recursive_symbolize_keys.rb

 def recursive_symbolize_keys! hash
   if hash.is_a? Hash
     hash.symbolize_keys!
     hash.values.each {|h| recursive_symbolize_keys! h}
   elsif hash.is_a? Array
     hash.map {|v| recursive_symbolize_keys! v}
   end
   hash
 end