Function lua_setmetatable

3rd/lua-5.4.3/src/lapi.c:927–964

LUA_API int lua_setmetatable (lua_State *L, int objindex) {
  TValue *obj;
  Table *mt;
  lua_lock(L);
  api_checknelems(L, 1);
  obj = index2value(L, objindex);
  if (ttisnil(s2v(L->top - 1)))
    mt = NULL;
  else {
    api_check(L, ttistable(s2v(L->top - 1)), "table expected");
    mt = hvalue(s2v(L->top - 1));
  }
  switch (ttype(obj)) {
    case LUA_TTABLE: {
      hvalue(obj)->metatable = mt;
      if (mt) {
        luaC_objbarrier(L, gcvalue(obj), mt);
        luaC_checkfinalizer(L, gcvalue(obj), mt);
      }
      break;
    }
    case LUA_TUSERDATA: {
      uvalue(obj)->metatable = mt;
      if (mt) {
        luaC_objbarrier(L, uvalue(obj), mt);
        luaC_checkfinalizer(L, gcvalue(obj), mt);
      }
      break;
    }
    default: {
      G(L)->mt[ttype(obj)] = mt;
      break;
    }
  }
  L->top--;
  lua_unlock(L);
  return 1;
}


LUA_API int lua_setiuservalue (lua_State *L, int idx, int n) {