export function groupIn<Key extends keyof T, T extends Record<string, any>>(
  array: T[],
  keyOrGetter: Key,
): Record<T[Key], T>
export function groupIn<T, KeyReturnT>(
  array: T[],
  keyOrGetter: (item: T) => KeyReturnT,
): KeyReturnT extends string | number ? Record<KeyReturnT, T> : never
export function groupIn<Key, T>(array: T[], keyOrGetter: Key) {
  let kv
  return array.reduce((r, a) => {
    kv = typeof keyOrGetter === 'function' ? keyOrGetter(a) : a[keyOrGetter as unknown as keyof T]
    // @ts-ignore
    r[kv] = a
    return r
  }, {})
}

export function groupBy<Key extends keyof T, T extends Record<string, any>>(
  array: T[],
  keyOrGetter: Key,
): Record<T[Key], T[]>
export function groupBy<T, KeyReturnT>(
  array: T[],
  keyOrGetter: (item: T) => KeyReturnT,
): KeyReturnT extends string | number ? Record<KeyReturnT, T[]> : never
export function groupBy<Key, T>(array: T[], keyOrGetter: Key) {
  let kv
  return array.reduce((r, a) => {
    kv = typeof keyOrGetter === 'function' ? keyOrGetter(a) : a[keyOrGetter as unknown as keyof T]
    // @ts-ignore
    r[kv] = [...(r[kv] || []), a]
    return r
  }, {})
}