    # File lib/facets/core/hash/having_fallback.rb, line 10
      def having_fallback(parent=nil)
        @fallback = parent
        unless @fallsback
          def self.[](key)
            return @fallback[key] if @fallback and not key?(key) rescue super
            super
          end
          def self.fetch(key, *args, &blk)
            return @fallback.fetch(key, *args, &blk) if @fallback and not key?(key) rescue super
            super
          end
          @fallsback = true
        end
        self
      end