How close to bug-free can you get?

1. Making Swift even safer

2. 18 months of development
120k+ lines of Swift
≈40 releases
6 months in production
Juno Rider iOS

3. Stricter interface

4. extension Array {
public subscript (safe index: Int) -> Element? { … }
}
extension Int {
public init?(safe value: Float) { … }
public init?(safe value: Double) { … }
public init?(safe value: UInt) { … }
}
!

5. NonEmptyString
NonEmptyArray
NonNegativeDouble
Stronger types

6. struct LocationCoordinate<A> {
let value: Double
init(_ value: Double) { self.value = value }
}
enum Lat {}
enum Lon {}
struct Location {
let latitude: LocationCoordinate<Lat>
let longitude: LocationCoordinate<Lon>
}
Phantom types

7. struct TaggedValue<ValueType, Tag> {
let value: ValueType
init(_ value: ValueType) { self.value = value }
}
enum PickupTimeTag {}
typealias PickupTime = TaggedValue<NSDate, PickupTimeTag>
enum DropoffTimeTag {}
typealias DropoffTime = TaggedValue<NSDate, DropoffTimeTag>
Phantom types

8. enum PhoneTag {}
typealias Phone = TaggedValue<String, PhoneTag>
extension TaggedValueType where Tag == PhoneTag, ValueType == String {
func trimCountryCode() -> Phone {
return Phone(trimCountryCode(self.taggedValue.value))
}
}
private func trimCountryCode(phone: String) -> String { … }
Phantom types

9. extension TaggedValueType where ValueType: JSONEncoding {
func encodeJSON() -> AnyObject {
return self.taggedValue.value.encodeJSON()
}
}
Phantom types

10. enum StringKey {
case AccessibilityHomeConfirmButton
case DialogInsufficientFundsTitle
...
}
func localized(value: Strings) -> String {
switch value {
case .AccessibilityHomeConfirmButton:
return String.localized(“Accessibility.Home.Confirm.Button”)
...
}
}
Static resources

11. extension HTTP {
enum Error: ErrorType {
case InvalidResponse(request: NSURLRequest, response: NSURLResponse?)
case TransportError(request: NSURLRequest, error: NSError)
case HTTPError(request: NSURLRequest, response: NSHTTPURLResponse, responseData: NSData?)
case CannotCreateURL(components: NSURLComponents)
case InvalidURL(urlString: String)
case AuthServiceFailure
case CannotBindStreamPair(request: NSURLRequest)
case StreamWriting(request: NSURLRequest, error: NSError?)
case StreamGzipEncoding(request: NSURLRequest, operation: HTTP.Error.GzipOperation)
}
}
Strong ErrorType

12. extension JSON.Error {
struct Encode: ErrorType {
public let error: NSError
public let source: Any
}
enum Decode: ErrorType {
case Unexpected
case Serialization(error: NSError, data: NSData)
case SchemeMismatch(error: JSON.Error.SchemeMismatch, body: AnyObject?)
}
struct SchemeMismatch: ErrorType {
public let pathComponents: [String]
public let reason: String
}
}
Strong ErrorType

13. public enum JSONTaskError: ErrorType {
case Task(error: HTTP.Error)
case Request(error: JSON.Error.Encode)
case Response(response: HTTP.Response, error: JSON.Error.Decode)
}
Strong ErrorType

14. Changing code

15. Components

16. Context
App

17. Context
May contain dirty things dealing with global state

18. Context
May contain dirty things dealing with global state
Unit tests

19. Context
typealias AppContext = protocol<
StringsServiceContainer,
StaticImageServicesContainer,
BundleImagesServiceContainer,
ReachabilityServiceContainer,
AnalyticsServiceContainer,
SchedulerContainer,
RemoteNotificationsContainer,
RemoteNotificationsPermissionContainer,
RemoteNotificationClearActionContainer,
LocationServiceContainer,
ApplicationServiceContainer,
DeviceServiceContainer,
…
>
class ElDependor: AppContext { … }
class MockContext: AppContext { … }

20. App
Pure state machine

21. App
Pure state machine
- Unit tests
- Integrated acceptance tests

22. Acceptance tests via TestApp
class Allow_Rider_to_Have_Max_X_Cards_per_Account_Spec: QuickSpec {
override func spec() {
var app: TestApp!
beforeEach { app = TestApp() }
given("rider is entering CC details on Add CC screen") {
beforeEach {
app.login()
app.goToHomeScreen()
app.receiveSomePaymentMethods()
app.openPayments()
app.payments.paymentMethods.tapAddPayment()
app.payments.addPayment.enterSomeCC()
app.payments.addPayment.tapNext()
app.payments.addPayment.enterSomeZipCode()
}
when("rider taps Add CC button") {
beforeEach { app.payments.addPayment.tapDone() }
and("BE returns the message about max number of active cards") {
beforeEach { app._context.addCreditCard.receive(.Failed(.TooManyPaymentMethods)) }
then("present the Max Cards Added alert") {
app.payments.addPayment.expectToPresentAlert()
}
when("rider taps Ok button") {
beforeEach { app.payments.addPayment.alert.tapOK() }
then("dismiss the alert") {
app.payments.addPayment.expectToNotPresentAlert()
}

24. View: screenshot testing

25. View: screenshot testing

26. View: screenshot testing

27. Detecting & investigating bugs in the field
- smart assertions
- diligent logging
- daily duty

28. junoAssert
in Debug - crash 🙀
in Release - log.error(), trackNonFatal() and recover 🙏

29. Logging
switch error {
case let .InvalidResponse(value):
log.warn(
category: logCategory,
message: "Unexpected response",
payload: [
.RequestIdentifier: error.requestIdentifier,
.ResponseIdentifier: error.responseIdentifier,
.Description: "(value.response)",
.Path: value.request.path,
.URL: value.request.absoluteURL
]
)
…

30. Logging
Analytics junoAssert
↓ ↓
log.verbose log.info log.warn log.error
↓ ↓ ↓ ↓
{'key0':'value0','key1':‘value1'}
↓
append to txt file
↓
roll & upload to AWS
↓
Elasticsearch + Kibana

31. Logging

32. Production quality comes at a price
- takes up to x2 dev effort
- challenging for new team members
- performance considerations

33. But it brings satisfaction

34. Thank you