UsersPostsUseCase.kt

data class CombinedUserPost(val user: User, val post: Post)

class UsersPostsUseCase @Inject constructor(
    private val userRepository: UserRepository,
    private val postRepository: PostRepository
) {

    fun get(refresh: Boolean): Single<List<CombinedUserPost>> =
        Single.zip(userRepository.get(refresh), postRepository.get(refresh),
            BiFunction { userList, postList -> map(userList, postList) })
}