type PropType<T, Path extends string> =
string extends Path ? unknown :
Path extends keyof T ? T[Path] :
Path extends `${infer K}.${infer R}` ? K extends keyof T ? PropType<T[K], R> : unknown :
unknown;
declare function getPropValue<T, P extends string>(obj: T, path: P): PropType<T, P>;
declare const s: string;
const obj = { a: { b: {c: 42, d: 'hello' }}};
getPropValue(obj, 'a'); // { b: {c: number, d: string } }
getPropValue(obj, 'a.b'); // {c: number, d: string }
getPropValue(obj, 'a.b.d'); // string
getPropValue(obj, 'a.b.x'); // unknown
getPropValue(obj, s); // unknown