Function checkupval

lib/lua/src/ldblib.c:285–295

** Check whether a given upvalue from a given closure exists and ** returns its index */

** returns its index
*/
static void *checkupval (lua_State *L, int argf, int argnup, int *pnup) {
  void *id;
  int nup = (int)luaL_checkinteger(L, argnup);  /* upvalue index */
  luaL_checktype(L, argf, LUA_TFUNCTION);  /* closure */
  id = lua_upvalueid(L, argf, nup);
  if (pnup) {
    luaL_argcheck(L, id != NULL, argnup, "invalid upvalue index");
    *pnup = nup;
  }
  return id;
}


static int db_upvalueid (lua_State *L) {