mrb_ary_plus(mrb_state *mrb, mrb_value self)
{
  struct RArray *a1 = mrb_ary_ptr(self);
  struct RArray *a2;
  const mrb_value *ptr;
  mrb_int blen, len1;

  mrb_get_args(mrb, "a", &ptr, &blen);
  if (ARY_MAX_SIZE - blen < ARY_LEN(a1)) {
    mrb_raise(mrb, E_ARGUMENT_ERROR, "array size too big");
  }
  len1 = ARY_LEN(a1);
  a2 = ary_new_capa(mrb, len1 + blen);
  array_copy(ARY_PTR(a2), ARY_PTR(a1), len1);
  array_copy(ARY_PTR(a2) + len1, ptr, blen);
  ARY_SET_LEN(a2, len1+blen);

  return mrb_obj_value(a2);
}