我想让react reducer函数更加通用，并将动作处理程序分离成函数。

export type Actions =
  | {
  type: "ADD_COLUMN";
  newColumnIndex: number;
  column: SelectorColumnData;
}
  | {
  type: "ITEM_CHECKED";
  columnIndex: number;
  item: SelectorItem;
};

export type ActionTypes = Actions["type"];
// type ActionTypes = "ADD_COLUMN" | "ITEM_CHECKED";

这对我来说很有意义：

const reducerRecord: Record<ActionTypes, (draft: Draft<SelectorState>, action: Actions) => void> = {
  "ITEM_CHECKED": itemCheckedAction,
  "ADD_COLUMN": addColumnAction,
};

export const selectorReducer: ImmerReducer<SelectorState, Actions> = (
  draft: Draft<SelectorState>,
  action: Actions,
): void => {
  reducerRecord[action.type](draft, action);
};

我的动作处理程序：

export const itemCheckedAction = (draft: Draft<SelectorState>, action: Actions) => {
  const { columnIndex, item } = action;
  // ...
}

TypeScript不喜欢这个（TS2339: property 'columnIndex' does not exist on type 'Actions'），所以我尝试了这个：

export const itemCheckedAction = (draft: Draft<SelectorState>, action: Actions) => {
  const { columnIndex, item }: Extract<Actions, { type: "ITEM_CHECKED" }> = action;
  // ...
}

也不喜欢这个！它说“ADD_COLUMN”类型丢失了。
奇怪的是，如果我写：

export const itemCheckedAction = (draft: Draft<SelectorState>, action: Actions) => {
  if(action.type === "ITEM_CHECKED") {
    const { columnIndex, item }: Actions = action;
  }
  // ...
}

...将鼠标悬停在= action上会显示所需的联合子类型，但IDE仍然抱怨columnIndex和item不是Actions的属性。
有什么想法吗？