具有对象文字和 Typescript 的功能性开关盒

Question

所以我在 todomvc 中有这个经典的 switch case redux reducer，我想使其功能化，但似乎无法为此考虑 ts 类型。

Switch case 非常适合模式匹配，并按类型缩小动作区分联合。但我似乎不知道如何使用功能方法传递缩小的操作，其中对象文字的键应该进行类型缩小。

到目前为止，我得到的是所有函数的联合类型和一些 ts 错误。非常感谢您对此事的任何帮助，以更好地了解如何在 ts 中使用严格类型。

import { action as actionCreator } from 'typesafe-actions';
import uuid from 'uuid';

import { ITodo } from 'types/models';

const ADD_TODO = 'todos/ADD_TODO';
const TOGGLE_ALL = 'todos/TOGGLE_ALL';
const REMOVE_TODO = 'todos/REMOVE_TODO';

export const addTodo = (title: string) => actionCreator(ADD_TODO, { title });
export const removeTodo = (id: string) => actionCreator(REMOVE_TODO, { id });
export const toggleAll = (checked: boolean) =>
  actionCreator(TOGGLE_ALL, { checked });

type TodosAction =
  | ReturnType<typeof addTodo>
  | ReturnType<typeof removeTodo>
  | ReturnType<typeof toggleAll>;
type TodosState = ReadonlyArray<ITodo>;

// no idea what typings should be
const switchCase = <C>(cases: C) => <D extends (...args: any[]) => any>(
  defaultCase: D
) => <K extends keyof C>(key: K): C[K] | D => {
  return Object.prototype.hasOwnProperty(key) ? cases[key] : defaultCase;
};

export default function(
  state: TodosState = [],
  action: TodosAction
): TodosState {
  // union type of 4 functions
  const reducer = switchCase({
    // (parameter) payload: any
    // How do I get types for these?
    [ADD_TODO]: payload => [
      ...state,
      {
        completed: false,
        id: uuid.v4(),
        title: payload.title,
      },
    ],
    [REMOVE_TODO]: payload => state.filter(todo => todo.id !== payload.id),
    [TOGGLE_ALL]: payload =>
      state.map(todo => ({
        ...todo,
        completed: payload.checked,
      })),
  })(() => state)(action.type);

  // [ts] Cannot invoke an expression whose type lacks a call signature. Type
  // '((payload: any) => { completed: boolean; id: string; title: any; }[]) |
  // ((payload: any) => ITodo[...' has no compatible call signatures.
  return reducer(action.payload);
}

Answer 1

一个有趣的打字问题。第一个关于负载类型的问题，我们可以通过传入所有可能的操作 (TodosAction) 来解决，并要求switchCase 的参数必须是一个映射类型，该类型将包含联合中所有types 的属性对于每种类型，我们可以使用Extract 条件类型来提取有效负载类型。

问题的第二部分是由于当您使用键（即联合类型本身）索引类型时，您会从该类型中获得所有可能值的联合。在这种情况下，这将是函数的联合，打字稿不认为是可调用的。为了解决这个问题，我们可以更改内部函数的公共签名以返回一个函数，该函数将所有有效负载的联合作为参数，而不是每个都采用有效负载的函数的联合。

结果看起来像这样：

import { action as actionCreator } from 'typesafe-actions';
import * as uuid from 'uuid';

interface ITodo{
    id: string
}

const ADD_TODO = 'todos/ADD_TODO';
const TOGGLE_ALL = 'todos/TOGGLE_ALL';
const REMOVE_TODO = 'todos/REMOVE_TODO';

export const addTodo = (title: string) => actionCreator(ADD_TODO, { title });
export const removeTodo = (id: string) => actionCreator(REMOVE_TODO, { id });
export const toggleAll = (checked: boolean) =>
    actionCreator(TOGGLE_ALL, { checked });

type TodosAction =
    | ReturnType<typeof addTodo>
    | ReturnType<typeof removeTodo>
    | ReturnType<typeof toggleAll>;
type TodosState = ReadonlyArray<ITodo>;

type Payload<TAll extends { type: any; payload: any }, P> = Extract<TAll, { type: P}>['payload']
type Casses<T extends { type: any; payload: any }, TState> = { [P in T['type']]: (payload: Payload<T, P>) => TState }


const switchCase = <C extends { type: any; payload: any }, TState>(cases: Casses<C, TState>) => 
    <D extends (payload: any) => TState >(defaultCase: D) => {
        function getCase <K extends string>(key: K): (arg: Payload<C, K>) => TState
        function getCase <K extends string>(key: K): Casses<C, TState>[K] | D {
            return cases.hasOwnProperty(key) ? cases[key] : defaultCase;
        }
        return getCase;
    };

export default function (
    state: TodosState = [],
    action: TodosAction
): TodosState {
    // union type of 4 functions
    const reducer = switchCase<TodosAction, TodosState>({
        [ADD_TODO]: payload => [
            ...state,
            {
                completed: false,
                id: uuid.v4(),
                title: payload.title,
            },
        ],
        [REMOVE_TODO]: payload => state.filter(todo => todo.id !== payload.id),
        [TOGGLE_ALL]: payload =>
            state.map(todo => ({
                ...todo,
                completed: payload.checked,
            })),
    })(() => state)(action.type);

    return reducer(action.payload);
}

Playground link