TypeScript Challenge - 实现一个通用MyReadonly2<T, K>，它带有两种类型的参数T和K

题目

实现一个通用MyReadonly2<T, K>，它带有两种类型的参数T和K。

K指定应设置为Readonly的属性集（如果T）。如果未提供K，则应使所有属性都变为只读，就像普通的Readonly<T>一样。

例如

interface Todo {
  title: string
  description: string
  completed: boolean
}

const todo: MyReadonly2<Todo, 'title' | 'description'> = {
  title: "Hey",
  description: "foobar",
  completed: false,
}

todo.title = "Hello" // Error: cannot reassign a readonly property
todo.description = "barFoo" // Error: cannot reassign a readonly property
todo.completed = true // OK

测试用例

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

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

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

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

答案

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

蒙圈了