8 - Readonly 2

// MyReadonly2<T, K>: Makes properties in K readonly, rest stay mutable.
// K defaults to keyof T (all keys) when omitted, behaving like Readonly<T>.
//
// Uses intersection (&) to split keys into two mapped types:
//   1. Keys IN K    → readonly
//   2. Keys NOT in K → mutable
//
// A single mapped type can't conditionally apply `readonly` per key,
// so we intersect two filtered mapped types instead.

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]
}