推断参数的类型以避免泛型？

Question

如何从作为参数传递的特定O中推断出obj？

export function pubsubs<O extends {[key: string]: Pubsub}>(
  obj: O // extends infer U ? U : never
   //        ↑
   //    (failed attempt to infer)
): {
  pub: Pubify<O>
  sub: Subify<O>
} {

  // ... generate pub and sub based on obj ...

  return {pub, sub}
}

所需结果：

const {pub, sub} = pubsubs({ // ← (want to infer from this first arg)
 //                      ↑
 //             (no generic)

  userLogout: pubsub(),
  userLoading: pubsub(),
  userError: pubsub<(error: Error) => void>(),
  userLogin: pubsub<(auth: LoginDetail) => void>(),
})

// but the typings fail to be inferred!
sub.userError(error => {})
 //            ↑
 //    (error type is 'any' )

没有推断的解决方法：

const input = {
  userLogout: pubsub(),
  userLoading: pubsub(),
  userError: pubsub<(error: Error) => void>(),
  userLogin: pubsub<(auth: LoginDetail) => void>(),
}

const {pub, sub} = pubsubs<typeof input>(input)
 //                         ↑
 //        (should be inferred)

// typings are preserved
sub.userError(error => {})
 //            ↑
 //       (typescript knows)

如何推断类型并避免使用泛型类型参数？