Experimenting with how to deeply un-readonly a type

UnReadOnly.ts

type Primitive = string | number | boolean | bigint | symbol | undefined | null
type Builtin = Primitive | Function | Date | Error | RegExp

type UnReadOnly<T> = {
  -readonly [K in keyof T]:
    T[K] extends Builtin
    ? T[K] 
    : T[K] extends Ref<infer U>
    ? Ref<UnReadOnly<U>>
    : T[K] extends ReadonlySet<infer U> 
    ? Set<UnReadOnly<U>>
    : T[K] extends Set<infer U>
    ? Set<UnReadOnly<U>>
    : T[K] extends ReadonlyMap<infer U, infer V>
    ? Map<U, UnReadOnly<V>>
    : T[K] extends Map<infer U, infer V>
    ? Map<U, UnReadOnly<V>>
    : T[K] extends object ? UnReadOnly<T[K]> : T[K]
}

type Test = {
  readonly name: string,
  readonly age: number,
  readonly children: string[],
  readonly address: {
    readonly street: string
    readonly zip: number
    readonly city: string
  },
  readonly items: ReadonlySet<string>
  readonly someref: Ref<string>
}


const test: Test = {
  name: 'Tom',
  age: 40,
  children: ['Tick', 'Trick', 'Track'],
  address: {
    street: 'main St.'
    zip: 12345,
    city: 'LA'
  },
  items: new Set(),
  someref: { value: 'hello' } as unknown as Ref<string>
}

// Readonly object:
test.address.street = 'Jerry'
test.items.add('stuff')

// removing readonly from all nested types
const test2: UnReadOnly<typeof test> = test

// mutable object, also for all neste properties
test2.address.city = 'london'
test2.children.push('Lisa')
test2.items.add('')


// Ref types only for exerimenting, normally defined in Vue core.
declare const RefSymbol: unique symbol
interface Ref<T = any> {
  value: T
  /**
   * Type differentiator only.
   * We need this to be in public d.ts but don't want it to show up in IDE
   * autocomplete, so we use a private Symbol instead.
   */
  [RefSymbol]: true
}