def freeze_strings!
      # Recursive visitor pattern helper.
      visitor = lambda do |val|
        case val
        when Hash
          val.each_value { |v| visitor.call(v) }
        when Array
          val.each { |v| visitor.call(v) }
        when String
          val.freeze
        end
      end
      visitor.call(@data)
    end
def freeze_strings!
      # Recursive visitor pattern helper.
      visitor = lambda do |val|
        case val
        when Hash
          val.each_value { |v| visitor.call(v) }
        when Array
          val.each { |v| visitor.call(v) }
        when String
          val.freeze
        end
      end
      visitor.call(@data)
    end
Freeze all string values in @data. This makes them immutable and saves
 a bit of RAM.

 @api private
 @return [void]