「重学TS 2.0 」TS 练习题第四十四题

[semlinker]

实现 Unpacked 工具类型，用于对类型执行 “拆箱” 操作。具体的使用示例如下所示：

type Unpacked<T> = // 你的实现代码

type T00 = Unpacked<string>;  // string
type T01 = Unpacked<string[]>;  // string
type T02 = Unpacked<() => string>;  // string
type T03 = Unpacked<Promise<string>>;  // string
type T04 = Unpacked<Unpacked<Promise<string>[]>>;  // string
type T05 = Unpacked<any>;  // any
type T06 = Unpacked<never>;  // never

请在下面评论你的答案

[zhaoxiongfei]

type Types = string | number | symbol;
type Unpacked<T> = T extends Types
  ? T
  : T extends (...arg: any) => infer R
    ? R
    : T extends Array<infer A>
      ? A
      : T extends Promise<infer P>
        ? P
        : never;

type T00 = Unpacked<string>;  // string
type T01 = Unpacked<string[]>;  // string
type T02 = Unpacked<() => string>;  // string
type T03 = Unpacked<Promise<string>>;  // string
type T04 = Unpacked<Unpacked<Promise<string>[]>>;  // string
type T05 = Unpacked<any>;  // any
type T06 = Unpacked<never>;  // never

我这个实现实话说很不满意，感觉完全是照着测试用例再写

[jackwangwj]

type Unpacked = T extends (...args: any) => infer A
? A
: T extends Promise《infer B》 // 《infer B》死活不显示，换成中文的尖括号示意下
? B
: T extends (infer A)[]
? A
: T

// 你的实现代码

type T00 = Unpacked; // string
type T01 = Unpacked<string[]>; // string
type T02 = Unpacked<() => string>; // string
type T022 = Unpacked<() => number>; // number
type T03 = Unpacked<Promise>; // string
type T032 = Unpacked<Promise>; // number
type T04 = Unpacked<Unpacked<Promise[]>>; // string
type T042 = Unpacked<Unpacked<Promise[]>>; // number
type T05 = Unpacked; // any
type T06 = Unpacked; // never

[zjxxxxxxxxx]

type Unpacked<T> = T extends Promise<infer V>
  ? Unpacked<V>
  : T extends () => void
  ? ReturnType<T>
  : T extends unknown[]
  ? T[number]
  : T;

[lq-math-dog]

// 疑问 没有理解到他们的写法
// 44 实现Unpacked工具类型，用于对类型执行 “拆箱” 操作。
type T00 = Unpacked; // string
type T01 = Unpacked<string[]>; // string
type T02 = Unpacked<() => string>; // string
type T03 = Unpacked<Promise>; // string
type T04 = Unpacked<Unpacked<Promise[]>>; // string
type T05 = Unpacked; // any
type T06 = Unpacked; // never
// 44.1
// type Unpacked = T extends Promise
// ? Unpacked
// : T extends () => void
// ? ReturnType
// : T extends unknown[]
// ? T[number]
// : T;
// // 关于T04解析
// // Unpacked<Promise[]> extends Promise
// type T07 = Unpacked<Promise[]> extends Promise ? true : false; //true
// // 这里为什么是true
// type T08 = Promise[] extends Promise ? true : false; //false
// type T09 = Promise extends Promise ? true : false; //true
// type Test = T
// type T071 = Test<Promise[]> extends Promise ? true : false; //false
// 44.2
type Unpacked = T extends (infer U)[]
? U
: T extends (...args: any[]) => infer U
? U
: T extends Promise
? U
: T;
// 关于T04解析
type T07 = Unpacked<Promise[]> extends (infer U)[] ? true : false;//false
type T08 = Unpacked<Promise[]> extends (...args: any[]) => infer U ? true : false;//false
type T09 = Unpacked<Promise[]> extends Promise ? true : false;//true