Closures¶

Intro¶

Closures are just a short hand version of functions in a function as a parameter passing around.

It is mostly used to run asynchronous methods and execute the closure function code only after receiving certain type of input from the parent function or service. You could say it is a synchronous method calling or promises type of behavior. In swift it is referred as “Completion handlers”

typealias Handler<OpenWeatherModel> = (Result<OpenWeatherModel, Error>) -> Void

func getWeatherDataByLatLon(latitudeWeather : Double, longitudeWeather : Double, completionHandler : @escaping Handler<OpenWeatherModel>) { 
            guard error == nil else { return completionHandler(.failure(error!)) }

            guard let data = data else { return }
            do {
                let response = try JSONDecoder().decode(OpenWeatherModel.self, from: data)
                completionHandler(.success(response))
            } catch let error {
                print("Error in retrieving data" + error.localizedDescription)
            }
        }
}

Calling closure

NetworkAPI.sharedInstance().getWeatherDataByLatLon(latitudeWeather : currLat, longitudeWeather: currLong, completionHandler : { [weak self] result in

            switch result {
            case .success(let data):
                print("In success block")
                self?.openWeatherResponse?.append(data)
                DispatchQueue.main.async {
                    self?.resultsTable.reloadData()
                }
            case .failure(let error): break
                // Check for internal error enum cases
                print("Some error occured")
            }


        })

Super in closure¶

Using 'super' in a closure where 'self' is explicitly captured is not yet supported

class Parent {
   func foo() {
   }
}

class Child: Parent {
   override func foo() {
      UIView.animateWithDuration(1) { [weak self] in // or any closure-producing context
         self?.super_foo()
      }
   }

   private func super_foo() {
      super.foo()
   }
}

Reference https://github.com/lionheart/openradar-mirror/issues/6765