Unionize.ts

import {Key} from '../Any/Key'
import {List} from './List'
import {At} from '../Any/At'

/**
 * Make the fields of `L` union the ones of `L1`
 * @param L to union from
 * @param L1 to union with
 * @param K (?=`Key`) to do choose fields
 * @returns [[List]]
 * @example
 * ```ts
 * ```
 */
export type Unionize<L extends List, L1 extends List, K extends Key = Key> = {
    [P in keyof L]: P extends K
                    ? L[P] | At<L1, P>
                    : L[P]
}