12. MyReadonly2

[astak16]

题目

题目链接：MyReadonly2

实现 MyReadonly2 ，接收两个参数，把第二个参数变为只读，同时第二个参数可以不传，不传的话就把第一个参数中所有的属性都变位只读。

import type { Alike, Expect } from "@type-challenges/utils";

type cases = [
  Expect<Alike<MyReadonly2<Todo1>, Readonly<Todo1>>>,
  Expect<Alike<MyReadonly2<Todo1, "title" | "description">, Expected>>,
  Expect<Alike<MyReadonly2<Todo2, "title" | "description">, Expected>>
];

interface Todo1 {
  title: string;
  description?: string;
  completed: boolean;
}

interface Todo2 {
  readonly title: string;
  description?: string;
  completed: boolean;
}

interface Expected {
  readonly title: string;
  readonly description?: string;
  completed: boolean;
}

答案

实现 MyReadonly2 类型，把 T 变位只读，用 Omit 从 T 中挑选出 K，最后使用 & 连接

方法一

type MyReadonly2<T, K extends keyof T = keyof T> = {
  readonly [key in K]: T[key];
} & Omit<T, K>;

方法二

type MyReadonly2<T, K extends keyof T = keyof T> = {
  readonly [key in K]: T[key];
} & {
  [key in K as key extends K ? key : never]: T[key];
};

方法三

type MyReadonly2<T, K extends keyof T = keyof T> = Readonly<T> & Omit<T, K>;