# Easy - Readonly

# question

Implement the built-in Readonly<T> generic without using it.

不要使用内置的 Readonly<T>，自己实现一个。

Constructs a type with all properties of T set to readonly, meaning the properties of the constructed type cannot be reassigned.

该 Readonly 会接收一个泛型参数 T，并返回一个完全一样的类型，只是所有属性都会被 readonly 所修饰。也就是不可以再对该对象的属性赋值。

For example:

interface Todo {
  title: string
  description: string
}

const todo: MyReadonly<Todo> = {
  title: "Hey",
  description: "foobar"
}

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

# answer

type MyReadonly<T> = {
  readonly [P in keyof T]: T[P]
}