Typescript 2.0.x与2.1.x，类型定义由switch / case语句过滤

@ ngrx / store（angular（2）的可观察到的redux实现）使用此模式将适当的类型传递给reducer

看到实际的代码

export const ActionTypes = {
  FOO:  type('foo'),
  BAR:  type('bar')
};

export class FooAction implements Action {
  type = ActionTypes.FOO;

  constructor(public payload: string) { }
}

export class BarAction implements Action {
  type = ActionTypes.BAR;

  constructor(public payload: number) { }
}

export type Actions
  = Foo
  | Bar;

以及减速器：

export class SomeReducerState {
  foo: string;
  bar: number;
}

const initialState = {
  foo: undefined,
  bar: 0
};

export function someReducer(
  state: SomeReducerState = initialState,
  action: some.Actions
): SomeReducerState {

  switch (action.type) {
    case some.ActionTypes.FOO:
      return Object.assign({}, state, { foo: action.payload });
    case some.ActionTypes.BAR:
      return Object.assign({}, state, { bar: action.payload });
    default:
      return state;
  }

}

它在typescript 2.0.x中的工作方式是（我认为）它将使用switch / case来决定/过滤出什么是正确的类型action.payload，所以insidecase some.ActionTypes.FOO action.payload是string，insideBAR是number。现在使用打字稿2.1.x似乎是any。有什么方法可以用2.1.x达到相同的结果？那是个错误吗？