If one really wanted that kind of behavior (and not getting errors when trying to add strings and number) you could make it so:

    class String
      def +(o)
        warn "You are adding a #{o.class} to a string." unless o.is_a? String
        "#{self}#{o}"
      end
    end

Whether this leads to other issues is left as an exercise for the reader and whomever ends up maintaining the reader's code.