def self.encode(uri, character_class=nil, returning=String)
      return nil if uri.nil?
      if !uri.respond_to?(:to_str)
        raise TypeError, "Can't convert #{uri.class} into String."
      end
      if ![String, ::Addressable::URI].include?(returning)
        raise TypeError,
          "Expected String or Addressable::URI, got #{returning.inspect}"
      end
      uri_object = uri.kind_of?(self) ? uri : self.parse(uri.to_str)
      encoded_uri = Addressable::URI.new(
        :scheme => self.encode_component(uri_object.scheme,
          character_class || Addressable::URI::CharacterClasses::SCHEME),
        :authority => self.encode_component(uri_object.authority,
          character_class || Addressable::URI::CharacterClasses::AUTHORITY),
        :path => self.encode_component(uri_object.path,
          character_class || Addressable::URI::CharacterClasses::PATH),
        :query => self.encode_component(uri_object.query,
          character_class || Addressable::URI::CharacterClasses::QUERY),
        :fragment => self.encode_component(uri_object.fragment,
          character_class || Addressable::URI::CharacterClasses::FRAGMENT)
      )