[buerkle]

foo(UUID, UUID); foo(AccountId, UserId);

I'd much rather deal with the 2nd version than the first. It's self-documenting and prevents errors like calling "foo(userId, accountId)" letting the compiler test for those cases. It also helps with more complex data structures without needing to create another type.

  Map<UUID, List<UUID>>
  Map<AccountId, List<UserId>>