如何使用打字稿为React Hooks组件编写Redux reducer？

Question

我正在尝试为类似redux的reducer建立类型。但是使用打字稿枚举作为映射接口的索引存在一个奇怪的问题。

// possible action types
enum ActionType {
  UpdateInterval,
  None,
  Test
}

// mapping interface [action-type]: data-type
interface ActionData {
  [ActionType.UpdateInterval]: Interval;
  [ActionType.None]: undefined,
  [ActionType.Test]: number;
}

// wrapper for type&data
interface Action<T extends ActionType> {
  type: T;
  data: ActionData[T]
}

// reduce function type
type ReduceMap<S extends State> = { [key in ActionType]: (state: S, data: ActionData[key]) => S };

// reduce process map (I prefer using object instead of switch)
const reduceMap : ReduceMap<State> = {
  [ActionType.UpdateInterval]: (state, data) => state,
  [ActionType.None]: (state, data) => state,
  [ActionType.Test]: (state, data) => state
};

// just reducer function
function reducer<T extends ActionType>(state: State, action: Action<T>) : State {        
  return reduceMap[action.type](state, action.data);
}

问题出在reducer函数内部：打字稿说第二个reduceMap函数参数的类型为never。 但我希望它类似于Interval | undefined | number。

Argument of type 'ActionData[T]' is not assignable to parameter of type 'never'. Type 'number | Interval | undefined' is not assignable to type 'never'. Type 'undefined' is not assignable to type 'never'.ts(2345)

我想从key（在ReduceMap类型）的ActionData接口获取数据类型时，会出现问题。但是我不知道如何解决它。