MobX-State-Tree 流程中的类型化 Yield 表达式

在 MobX-state-tree (MST) 中执行异步操作的推荐方法是使用flow https://mobx-state-tree.js.org/concepts/async-actions，它接受一个生成器函数作为第一个参数，其中每个承诺都应该被产生。

yield表达式具有类型any在打字稿中 https://github.com/Microsoft/TypeScript/issues/2983#issuecomment-230414026，但是有没有办法在MST中自动输入yield表达式呢？

Example

import { flow, types } from "mobx-state-tree";

type Stuff = { id: string; name: string };

function fetchStuff(): Promise<Stuff[]> {
  return new Promise((resolve) => {
    resolve([
      { id: "1", name: "foo" },
      { id: "2", name: "bar" }
    ]);
  });
}

const Thing = types.model({
  id: types.identifier,
  name: types.string
});

const ThingStore = types
  .model({
    things: types.array(Thing)
  })
  .actions((self) => ({
    fetchThings: flow(function* () {
      // "stuff" is of type "any"!
      const stuff = yield fetchStuff();
      self.things.replace(stuff);
    })
  }));

到发电机 https://mobx-state-tree.js.org/API/#togenerator可用于将 Promise 转换为生成该 Promise 的生成器。这与yield*代替yield（可通过设置downlevelIteration to true在 TypeScript 编译器选项中 https://www.typescriptlang.org/docs/handbook/compiler-options.html#compiler-options) 使得 Promise 返回类型得以保留。

import { flow, types, toGenerator } from "mobx-state-tree";

type Stuff = { id: string; name: string };

function fetchStuff(): Promise<Stuff[]> {
  return new Promise((resolve) => {
    resolve([
      { id: "1", name: "foo" },
      { id: "2", name: "bar" }
    ]);
  });
}

const Thing = types.model({
  id: types.identifier,
  name: types.string
});

const ThingStore = types
  .model({
    things: types.array(Thing)
  })
  .actions((self) => ({
    fetchThings: flow(function* () {
      // "stuff" is now of type "Stuff[]"!
      const stuff = yield* toGenerator(fetchStuff());
      self.things.replace(stuff);
    })
  }));