003.对象部分属性只读

实现一个泛型 MyReadonly2<T, K>，它带有两种类型的参数 T 和 K

类型 K 指定 T 中要被设置为只读（readonly）的属性。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

答案

// 答案 1
type MyReadonly2<T, K extends keyof T = keyof T> = Readonly<Pick<T, K>> & Omit<T, K>
 
// 答案 2
type MyReadonly2<T, K extends keyof T = keyof T> = {
  readonly [P in keyof T as P extends K ? P : never]: T[P]
} & {
  [P in keyof T as P extends K ? never : P]: T[P]
}