rails/rails/blob/4-2-stable/activesupport/lib/active_support/core_ext/hash/keys.rb

keys.rb

class Hash
  def transform_keys
    return enum_for(:transform_keys) unless block_given?
    result = self.class.new
    each_key do |key|
      result[yield(key)] = self[key]
    end
    result
  end

  def symbolize_keys
    transform_keys{ |key| key.to_sym rescue key }
  end
  alias_method :to_options,  :symbolize_keys
end