00009-medium-deep-readonly.ts

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

type cases = [
    Expect<Equal<DeepReadonly<X1>, Expected1>>,
    Expect<Equal<DeepReadonly<X2>, Expected2>>
];

type X1 = {
    a: () => 22;
    b: string;
    c: {
        d: boolean;
        e: {
            g: {
                h: {
                    i: true;
                    j: "string";
                };
                k: "hello";
            };
            l: [
                "hi",
                {
                    m: ["hey"];
                }
            ];
        };
    };
};

type X2 = { a: string } | { b: number };

type Expected1 = {
    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"];
                }
            ];
        };
    };
};

type Expected2 = { readonly a: string } | { readonly b: number };

// ============= Your Code Here =============
type DeepReadonly<T> = {
    readonly [K in keyof T]: keyof T[K] extends never
        ? T[K]
        : DeepReadonly<T[K]>;
};