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public suspend fun ProducerScope<*>.awaitClose(block: () -> Unit = {}) {
  ...
  try {
    // Suspend the coroutine with a cancellable continuation
    suspendCancellableCoroutine<Unit> { cont ->
      // Suspend forever and resume the coroutine successfully only 
      // when the Flow/Channel is closed
      invokeOnClose { cont.resume(Unit) }
    }
  } finally {

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val FusedLocationProviderClient.locationFlow() = callbackFlow<Location> {
  ...
}.shareIn(
  // Make the flow follow the applicationScope
  applicationScope,
  // Emit the last emitted element to new collectors
  replay = 1,
  // Keep the producer active while there are active subscribers
  started = SharingStarted.WhileSubscribed()
)

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@ViewModelScoped // Scopes type to the ViewModel
class UserInputAuthData(
  private val handle: SavedStateHandle // Default binding in ViewModelComponent
) { /* Cached data and logic here */ }

class RegistrationViewModel(
  private val userInputAuthData: UserInputAuthData,
  private val validateUsernameUseCase: ValidateUsernameUseCase,
  private val validatePasswordUseCase: ValidatePasswordUseCase
) : ViewModel() { /* ... */ }

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@Module
@InstallIn(ViewModelComponent::class)
object UserAuthModule {

  @Provides
  fun provideValidateUsernameUseCase(
    userInputAuthData: UserInputAuthData, // scoped to ViewModelComponent
    repository: UserRepository
  ): ValidateUsernameUseCase {
    return ValidateUsernameUseCaseImpl(userInputAuthData, repository)

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class TransactionsRepository(
  private val defaultDispatcher: CoroutineDispatcher = Dispatchers.Default
) {

  private val transactionsCache = mutableMapOf<User, List<Transaction>()

  private suspend fun addTransaction(user: User, transaction: Transaction) =
    // CAREFUL! Access to the cache is not protected.
    // Concurrency bugs can happen: threads can see stale data
    // and race conditions may occur.

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class TransactionsRepository(
  private val defaultDispatcher: CoroutineDispatcher = Dispatchers.Default
) {

  // Mutex protecting the cache mutable state
  private val cacheMutex = Mutex()
  private val transactionsCache = mutableMapOf<User, List<Transaction>()

  private suspend fun addTransaction(user: User, transaction: Transaction) =
    withContext(defaultDispatcher) {

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// Implementation of a cold flow backed by a Channel that sends Location updates
fun FusedLocationProviderClient.locationFlow() = callbackFlow<Location> {
    val callback = object : LocationCallback() {
        override fun onLocationResult(result: LocationResult?) {
            result ?: return
            try { offer(result.lastLocation) } catch(e: Exception) {}
        }
    }
    requestLocationUpdates(createLocationRequest(), callback, Looper.getMainLooper())
        .addOnFailureListener { e ->

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class LocationActivity : AppCompatActivity() {

    // Coroutine listening for Locations
    private var locationUpdatesJob: Job? = null

    override fun onStart() {
        super.onStart()
        locationUpdatesJob = lifecycleScope.launch {
            locationProvider.locationFlow().collect {
                // New location! Update the map

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class LocationActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // Collects from the flow when the lifecycle is at least STARTED and
        // STOPS the collection when it's STOPPED.
        // It automatically restarts collecting when the lifecycle is STARTED again.
        lifecycleOwner.addRepeatingJob(Lifecycle.State.STARTED) {
            locationProvider.locationFlow().collect {
                // New location! Update the map

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class LocationFragment: Fragment() {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        // ...
        viewLifecycleOwner.addRepeatingJob(Lifecycle.State.STARTED) {
            locationProvider.locationFlow().collect {
                // New location! Update the map
            } 
        }
    }
}