參數名稱能否成為Swift 4中的返回類型？

Question

Hi there！I meet the following code in IOS swift development class. 

class UpdateToAttributedStringsPolicy: NSEntityMigrationPolicy {

override func createDestinationInstances(forSource sInstance: NSManagedObject, in mapping: NSEntityMapping, manager: NSMigrationManager) throws {
    // Call super
    try super.createDestinationInstances(forSource: sInstance, in: mapping, manager: manager)

    // Get the (updated) destination Note instance we're modifying
    guard let destination = manager.destinationInstances(forEntityMappingName: mapping.name, sourceInstances: [sInstance]).first else { return }

    // Use the (original) source Note instance, and instantiate a new
    // NSAttributedString using the original string
    if let text = sInstance.value(forKey: "text") as? String {
        destination.setValue(NSAttributedString(string: text), forKey: "attributedText")
    }
  }
}

在這行代碼中

override func createDestinationInstances(forSource sInstance: NSManagedObject, in mapping: NSEntityMapping, manager: NSMigrationManager) throws

sInstance和manager是函數createDestinationInstances中的參數名稱，但在

try super.createDestinationInstances(forSource: sInstance, in: mapping, manager: manager)

他們成為一個退貨名稱，這是如何工作的？ 為什么在這里調用super呢？

謝謝！

Answer 1

如果我理解正確，那么您正在問如何將sInstance用作值，即使它只是標簽？

如前所述這里 （函數聲明- >參數名稱部分），該sInstance實際上是一個參數名稱，而不是標簽。

parameter_name: parameter_type
argument_label parameter_name: parameter_type
_ parameter_name: parameter_type

所以雖然這是正確的

try super.createDestinationInstances(forSource: sInstance, in: mapping, manager: manager)

這是錯誤的：

 try super.createDestinationInstances(forSource: forSource, in: in, manager: manager)