polac24

// Custom RawRepresentable type for BestEnum
struct BestEnumRaw: ExpressibleByStringLiteral{
    let rawString:String?
    
    init(){
        rawString = nil
    }
    
    init(stringLiteral value: String){
        rawString = value

polac24

func testDownloaderCallsCompletionOnResponse(){
    // Arange
    let url = URL(string: "https://address.com")!
    let completionExpectation = expectation(description: "completionExpectation")
    
    // Act
    let downloader = Downloader(url:url, completionHandler:{
        completionExpectation.fulfill()
    })
    networkLayer.responseWithJSON(json:{})

polac24

class ReferenceObserver{
    private let deinitHandler:()->()
    
    init(deinitHandler:@escaping ()->()) {
        self.deinitHandler = deinitHandler
    }
    deinit {
        deinitHandler()
    }
}

polac24

// Arange
let url = URL(string: "https://address.com")!
let deinitExpectation = expectation(description: "deinit completionHandler")
var reference:ReferenceObserver? = ReferenceObserver(deinitHandler: deinitExpectation.fulfill)

// Act
let downloader = Downloader(url:url, completionHandler:{[capturedReference = reference] in
    _ = capturedReference
    XCTFail()
})

polac24

func testDownloaderDoesNotCallCompletionOnCancelledDownload(){
    // Arange
    let url = URL(string: "https://address.com")!
    let deinitExpectation = expectation(description: "deinit completionHandler")
    var reference:ReferenceObserver? = ReferenceObserver(deinitHandler: deinitExpectation.fulfill)
    let downloader = Downloader(url:url, completionHandler:{[capturedReference = reference] in
        _ = capturedReference
        XCTFail()
    })
    reference = nil

polac24

class ReferenceObserver{
    private let deinitHandler:()->()
    private var allowedToDealloc = false
    
    init(deinitHandler:@escaping ()->()) {
        self.deinitHandler = deinitHandler
    }
    deinit {
        guard allowedToDealloc else {
            XCTFail("ReferenceObserver deallocated too early!")

polac24

func testDownloaderDoesNotCallCompletionOnCancelledDownload(){
    // Arange
    let url = URL(string: "https://address.com")!
    let deinitExpectation = expectation(description: "deinit completionHandler")
    let downloader:Downloader
    do {
        let reference = ReferenceObserver(deinitHandler: deinitExpectation.fulfill)
        downloader = Downloader(url:url, completionHandler:{[capturedReference = reference] in
            _ = capturedReference
            XCTFail()

polac24

let error = // some error received in a completion handler
switch (error) {
  case .invalidValue:
    // highlight textfield that user has to modify
  case .noInternet:
    // present an alert
  case .sessionInvalidated:
    // pass error to the parent layer (e.g. by delegate)
    delegate.didObserveInvalidatedSession()
}

polac24

public typealias HandleAction<T> = (T) throws -> ()
public protocol ErrorHandleable: class{
  func `throw`(_ :Error, finally: @escaping (Bool)->Void)
  func `catch`(action: @escaping HandleAction<Error>) -> ErrorHandleable
}

polac24

let previousErrorHandler:ErrorHandleable = /// existing handler
// setup a handler
let errorHandler = previousErrorHandler.catch {error in
  // Log all errors into console and pass it further
  print(error)
  throw error
}.catch {
  // Stop propagation for all errors(no throwing)
}
...