Swift subclassing - how to override Init()

Question

I have the following class, with an init method:

class user {
  var name:String
  var address:String

  init(nm: String, ad: String) {
    name = nm
    address          


        

Answer 1

In swift 2.0 and Later it works like this (all cases)

init(newString:String) {
    super.init(string:newString)
    // Designed initialiser 
}
override init(someString: String) {
    super.init(mainString: someString)
    // Override initialiser when subclass some class 
}
required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
    // Some boilerplate code to handle error (needed when override)
}
convenience init(newString:String, withParameters:Dictionary<String,String>) {
    self.init(someString:newString)
    //Convenience initialiser 
}

Answer 2

Have you tried setting a value to numberPriorVisits and changing the types for the calls to super

class user {
    var name:String
    var address:String

    init(nm: String, ad: String) {
        name = nm
        address = ad
    }
}


class registeredUser : user {
    var numberPriorVisits: Int;

    init(nm: String, ad: String) {
        self.numberPriorVisits = 0;
        super.init(nm: nm, ad: ad)
    }
}

Answer 3

You pass arguments to an initializer much like you pass arguments to a normal method:

init(nm: String, ad: String) {  
    super.init(nm: nm, ad: ad) 
}

For reference, this is shown in the Designated and Convenience Initializers In Action section of the Swift Language Guide.

Answer 4

In addition to Chuck's answer, you also have to initialize your new introduced property before calling super.init

A designated initializer must ensure that all of the properties introduced by its class are initialized before it delegates up to a superclass initializer. (The Swift Programming Language -> Language Guide -> Initialization)

Thus, to make it work:

init(nm: String, ad: String) {
    numberPriorVisits = 0  
    super.init(nm: nm, ad: ad) 
}

This simple initialization to zero could have been done by setting the property's default value to zero too. It's also encouraged to do so:

var numberPriorVisits: Int = 0

If you don't want such a default value it would make sense to extend your initializer to also set a new value for the new property:

init(name: String, ads: String, numberPriorVisits: Int) {
    self.numberPriorVisits = numberPriorVisits
    super.init(nm: name, ad: ads)
}