Refer: Easy - Readonly

Relation: Medium - Readonly-2

Describe

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

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

For example

code snippetCopyjavascript
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

Test Cases

code snippetCopytypescript
import { Equal, Expect } from '@type-challenges/utils'

type cases = [Expect<Equal<MyReadonly<Todo1>, Readonly<Todo1>>>]

interface Todo1 {
  title: string
  description: string
  completed: boolean
  meta: {
    author: string
  }
}

Solution

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