Recursifies an object on to another object in Typescript

recursify-onto.type.ts

/**
 * T: The normal object to apply O to at every nested object
 *
 * @example
export const OBJECT_ID = Symbol('_objectId');

export interface IHasOBJECT_ID {
  [OBJECT_ID]: UUID;
}

interface John {
  john: {
    name: string,
    address: {
      num: number,
      street: string,
      town: {
        name: string,
        population: number,
      },
    },
  },
}

const john: RecursifyOnto<John, IHasOBJECT_ID> = {
  john: {
    name: 'john',
    address: {
      town: {
        name: 'hi',
        population: 5,
        [OBJECT_ID]: 'id',
      },
      num: 1,
      street: 'A street',
      [OBJECT_ID]: 'id',
    },
    [OBJECT_ID]: 'id',
  },
  [OBJECT_ID]: 'id',
};
 */
export type RecursifyOnto<T, O> = {
  [P in keyof T]: T[P] extends string ? T[P] :
    T[P] extends number ? T[P] :
      T[P] extends boolean ? T[P] :
        T[P] extends undefined ? T[P] :
          T[P] extends Function ? T[P] :
            RecursifyOnto<T[P], O> & O
} & (T extends string ? T :
  T extends number ? T :
    T extends boolean ? T :
      T extends undefined ? T :
        T extends Function ? T :
          O);