00009-medium-deep-readonly.ts

// ============= Test Cases =============
import type { Equal, Expect } from './test-utils';

type cases = [Expect<Equal<DeepReadonly<X>, Expected>>];

type X = {
  a: () => 22;
  b: string;
  c: {
    d: boolean;
    e: {
      g: {
        h: {
          i: true;
          j: 'string';
        };
        k: 'hello';
      };
      l: [
        'hi',
        {
          m: ['hey'];
        }
      ];
    };
  };
};

type Expected = {
  readonly a: () => 22;
  readonly b: string;
  readonly c: {
    readonly d: boolean;
    readonly e: {
      readonly g: {
        readonly h: {
          readonly i: true;
          readonly j: 'string';
        };
        readonly k: 'hello';
      };
      readonly l: readonly [
        'hi',
        {
          readonly m: readonly ['hey'];
        }
      ];
    };
  };
};

// ============= Your Code Here =============
type DeepReadonly<T> = T extends Function
  ? T
  : {
      readonly [K in keyof T]: T[K] extends object ? DeepReadonly<T[K]> : T[K];
    };