Deep Readonly

In this medium-level challenge, you'll implement a generic DeepReadonly<T>, which makes every parameter of an object - and its sub-objects recursively - readonly.

type X = {
x: {
a: 1
b: 'hi'
}
y: 'hey'
}
 
type Expected = {
readonly x: {
readonly a: 1
readonly b: 'hi'
}
readonly y: 'hey'
}
 
type Todo = DeepReadonly<X> // should be same as `Expected`

Detailed Explanation

To make an object deeply readonly, we need recursion:

type DeepReadonly<T> = T extends Function
  ? T
  : {
      readonly [K in keyof T]: DeepReadonly<T[K]>
    }

How it works:

• If the type is a Function, leave it as is
• Otherwise, we create a mapped type that iterates over all properties of the type T and applies the readonly modifier to them
• The DeepReadonly type is applied recursively to the values of the type T

This challenge helps you understand readonly modifiers and how to apply this concept in real-world scenarios.