dot args types

dot-types-example.ts

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

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

type PathValue<T, P extends Path<T>> =
  P extends `${infer K}.${infer Rest}`
  ? K extends keyof T
    ? Rest extends Path<T[K]>
      ? PathValue<T[K], 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;

get(object, "firstName"); // works
get(object, "projects.0"); // works
get(object, "projects.0.name"); // works

get(object, "role"); // type error