关于类型诊断的默认行为.

[CandyMi]

在loslib.c内的345行附近可以找到lua库函数os.time的C实现如下:

static int os_time (lua_State *L) {
  time_t t;
  if (lua_isnoneornil(L, 1))  /* called without args? */
    t = time(NULL);  /* get current time */
  else {
    struct tm ts;
    luaL_checktype(L, 1, LUA_TTABLE);
    lua_settop(L, 1);  /* make sure table is at the top */
    ts.tm_year = getfield(L, "year", -1, 1900);
    ts.tm_mon = getfield(L, "month", -1, 1);
    ts.tm_mday = getfield(L, "day", -1, 0);
    ts.tm_hour = getfield(L, "hour", 12, 0);
    ts.tm_min = getfield(L, "min", 0, 0);
    ts.tm_sec = getfield(L, "sec", 0, 0);
    ts.tm_isdst = getboolfield(L, "isdst");
    t = mktime(&ts);
    setallfields(L, &ts);  /* update fields with normalized values */
  }
  if (t != (time_t)(l_timet)t || t == (time_t)(-1))
    return luaL_error(L, "time result cannot be represented in this installation");
  l_pushtime(L, t);
  return 1;
}

但是我发现os.time({}) 构造参数时会诊断为"缺少字段". 这似乎与实现的默认行为有些出入.

然后我查看了一下osdate的定义, 个人认为可以加上?来保证默认诊断与函数的实现行为一致. 例如这样：