Typescript如何实现下图这种类型推断

Question

期望下图get函数根据传入的url自动推导出返回值类型

//源码
type Api = {
    a: () => { x: string, y: string },
    b: () => number,
};

const api: Api = {
    a() {
        return { x: "xxx", y: "yyy" }
    },
    b() {
        return 222
    },
}

function get<K extends keyof Api>(key: K) {
    return api[key]();
}

const foo = get("a")

Answer 1

type Api = {
  a: () => { x: string; y: string }
  b: () => number
}

const api: Api = {
  a() {
    return { x: 'xxx', y: 'yyy' }
  },
  b() {
    return 222
  },
}

function get<K extends keyof Api>(key: K) {
  return api[key]() as ReturnType<Api[K]>
}