The goal of Initializers

App Development
1

Hi,

I’m having a hard time understanding initializers and why they even exist. I have a couple of questions:

  1. In lesson 10, I learned about classes and subclasses. There I learned how to use so-called “templates”. I also learned you could create a new object from (like in this lesson) the Manager class for example. You can create a new manager by saying var m = Manager() and then say m.name() = “Maggie” and then create a new manager by saying n = Manager() and say n.name() = “Jonathan”
    My question:
  • why do initializers exist if you can do it this way? When do I declare a new object / person inside the class, when do I do it outside the class and when do I use the initializer method over the way we did it in the lesson about classes and subclasses? I realize you said that they exist to your objects are ready to be used, but what does that mean?
  1. In lesson 12, I get an error after writing the exact same code as in the lesson where you Chris, didn’t get an error. The code I wrote down:

import UIKit

class Person {
** var name = “”**
** init() {**
** }**
** init( name:String) {**
** self.name = name**
** }**
}

class Employee: Person {

** var salary = 0**
** var role = “”**

** override init( name:String) {**

** // This is calling the init( name:String) function of the Person class**
** super.init(name)**

** // Additional init code**
** self.role = “Analyst”**
** }**
** func doWork() {**
** print(“Hi, my name is (name) and I’m doing work.”)**
** salary += 1**
** }**
}

class Manager: Employee {
** var teamSize = 0**
** override func doWork() {**
** super.doWork()**
** print(“I’m managing people”)**
** salary += 2**
** }**
** func firePeople() {**
** print(“I’m firing people”)**
** }**
** }**

let myPerson = Person(name: “Tom”)
print(myPerson.name)

let myEmployee = Employee(name: “Joe”)
print(myEmployee.role)
print(myEmployee.name)

Xcode then gives me an error (Missing argument label ‘name:’ in call) on the line that says “super.init(name)”. I fixed this by writing down “super.init(name:name)” instead and then it works. But why is this?

2

Because assigning values to properties isn’t the only thing initializers can do.

Your struct or class might have internal properties that you don’t want to expose in this way.
Or it might have constants that can be given a value during initialization but not after.
Or something needs to be calculated and assigned depending on the values you pass in to the initializer.
Or anything else that has to be done so that your struct/class is a valid instance of that type before you try to use it in your code.

If a method or function has a named parameter, you have to use that name when you call it. If a function parameter has an argument label, then you have to use that label when you call it. The only time you don’t have to use either a parameter name or an argument label is if the parameter has an argument label of _.

To demonstrate:

func doWork(action: String) { print(action) }
doWork(action: "fold")

func doWork(agendaItem action: String) { print(action) }
doWork(agendaItem: "spindle")

func doWork(_ action: String) { print(action) }
doWork("mutilate")

Does that make sense?

Also, for future posting, note that you should fence off your code using backticks to format it properly. Place three backticks ``` on the line before and the line after your code. It was really difficult to read your code with all the asterisks around each line.

import UIKit

class Person {
    var name = “”
    
    init() {
    }
    
    init( name:String) {
        self.name = name
    }
}

class Employee: Person {

    var salary = 0
    var role = “”

    override init( name:String) {

        // This is calling the init( name:String) function of the Person class
        super.init(name)

        // Additional init code
        self.role = “Analyst”
    }

    func doWork() {
        print(“Hi, my name is (name) and I’m doing work.”)
        salary += 1
    }
}

class Manager: Employee {
    var teamSize = 0

    override func doWork() {
        super.doWork()
        print(“I’m managing people”)
        salary += 2
    }

    func firePeople() {
        print(“I’m firing people”)
    }
}

let myPerson = Person(name: “Tom”)
print(myPerson.name)

let myEmployee = Employee(name: “Joe”)
print(myEmployee.role)
print(myEmployee.name)

See how easier it is to read? (I also added some extra spacing and indentation to make it even more readable).

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