PostRepositoryImpl.kt

@Singleton
class PostRepositoryImpl @Inject constructor(
    private val cacheDataSource: PostCacheDataSource,
    private val remoteDataSource: PostRemoteDataSource
) : PostRepository {

    override fun get(refresh: Boolean): Single<List<Post>> =
        when (refresh) {
            true -> remoteDataSource.get()
                .flatMap { cacheDataSource.set(it) }
            false -> cacheDataSource.get()
                .onErrorResumeNext { get(true) }
        }
}