Typed get. Dot notation string type-safe

get.ts

// https://tsplay.dev/WvaG4m
// Source: https://github.com/ghoullier/awesome-template-literal-types#dot-notation-string-type-safe

// alternative: https://github.com/g-makarov/dot-path-value


type PathImpl<T, Key extends keyof T> =
  Key extends string
  ? T[Key] extends Record<string, any>
    ? | `${Key}.${PathImpl<T[Key], Exclude<keyof T[Key], keyof any[]>> & string}`
      | `${Key}.${Exclude<keyof T[Key], keyof any[]> & string}`
    : never
  : never;

type PathImpl2<T> = PathImpl<T, keyof T> | keyof T;

type Path<T> = PathImpl2<T> extends string | keyof T ? PathImpl2<T> : keyof T;

type PathValue<T, P extends Path<T>> =
  P extends `${infer Key}.${infer Rest}`
  ? Key extends keyof T
    ? Rest extends Path<T[Key]>
      ? PathValue<T[Key], Rest>
      : never
    : never
  : P extends keyof T
    ? T[P]
    : never;

declare function get<T, P extends Path<T>>(obj: T, path: P): PathValue<T, P>;

const object = {
  firstName: "Diego",
  lastName: "Haz",
  age: 30,
  projects: [
    { name: "Reakit", contributors: 68 },
    { name: "Constate", contributors: 12 },
  ]
} as const;

const lol = get(object, "projects.0");
//    ^?