def visit_this_0(receiver, thing)
    if method_name = @cache[thing.class]
      return receiver.send(method_name, thing)
    end
    visit_this(receiver, thing, NO_ARGS)
  end
def visit_this_0(receiver, thing)
    if method_name = @cache[thing.class]
      return receiver.send(method_name, thing)
    end
    visit_this(receiver, thing, NO_ARGS)
  end
Visit an explicit receiver with 0 args
 (This is ~30% faster than calling the general method)