why do we need initalizers?

Isn't it us programmers give the value to the stored properties when we create instances of structs? I still don't get how initializers work.

Hi Chi:

In order for you to be able to create an instance of a class, or struct, you need to give values to their store properties correct ? Well, that's what the initializer are for, to INITIALIZE the store properties. Therefore a complete instance will be created.

For example.

class SomeClass {

// Store properties with no values
    var storePropertie: Int?
    var storePropertie2: Int?

    init(initializeFirst: Int, initializeSecond: Int){
        storePropertie = initializeFirst
        storePropertie2 = initializeSecond
    }

}


// Creating an instance of SomeClass
var instanceOfSomeClass = SomeClass(initializeFirst: 3, initializeSecond: 5)

// Accessing the instance's store properties
instanceOfSomeClass.storePropertie // has a value of 3 now
instanceOfSomeClass.storePropertie2 // has a value of 5 now

We now have created a proper class, and also created an instance of it via its initializer.

If you have any more questions, please let me know.

Good luck

Now I get it, when we give the value to the instance, it goes to the value in the init function. I've always thought it will go straight to the stored properties itself. Thank you so much :D.

Hello Jhoan: I still have some questions though... I thought initialize is like giving a value to the constant or variety we declare before. But it seems like you just declare another variety for the first one (like, storePropertie = initializeFirst). I just can't get the reason why we do that. Why we don't give a number, for example "5" as it's a Int here? It really bothers me a lot...

thanks a lot!

Hello Kuang-Wen:

You are right, initialize is when you first declare a variable or a constant, and you give it an initial value. But when creating a class or a struct you may declare a variable within the class and not give it an initial value. This can be done by making it an optional.

Let's create a class ( Person ), this class creates an object or in this case a Person. This class has 3 store properties, which 2 ( name & lastName ) of them are being set up to be initialized ( or given a value ) by the initializer. The third store property ( age ) which is of type int, has no initial value nor is being set up by the initializer. But since it's a variable and IT'S an optional, it does not required to be initialized in order for you to create an instance of Person.

Example:

class Person {

    // Name Properties
    let name: String
    let lastName: String

    // Age propertie
    var age: Int?

    // Initializer for the names only
    init(name: String, lastName: String){
        self.name = name
        self.lastName = lastName
    }
}

// Instances of Person

let man = Person(name: "Frank", lastName: "Sinatra")
let woman = Person(name: "Tonya", lastName: "Jackson")


// Accessing each instances properties

man.name // Frank
man.lastName // Sinatra
man.age // nil

// Notice how man.age has no value, only name and lastNames have values.
// Now let's give age a value directly 

man.age = 35

// we gave man an age of 35, now if you call it, it will return his age.

man.age // 35

I encourage you to copy this code and paste it into a playground in Xcode, it will make more sense to you.

If you have another question about this, please let me know by tagging me or ask a more detailed question in the forum and then tag my name on there @jhoanarango

Good luck and hope this helps

Hello, Jhoan Arango First of all thanks for your instant help! Now it really make sense. But there is another question I want to know. Why "var" don't need to be initialized while "let" need to be? I have rewrite your code in the playground and find out that if var something is an OPTIONAL, than without initialized will be Okay, but it doesn't work on let something. What's the different? Can't "let something?" output nil without being initialized?

Again, thanks a lot! The codes you write is clear and very helpful! Also please forgive my bad English!

Hello:

The age property is an optional Int property, and so it automatically receives a default value of nil, even though this value is not written in the code. If this was to be done with a constant, then it's value could have not been changed during initialization. That's why you can't make a constant an optional, because then they will always be "nil".

I hope this answers your question.

color.description gives the output "red: 86.0, green: 191.0, blue: 131.0, alpha: 1.0"

Hello :

Try deleting the self. out of the concatenation.

        self.description = "red: \(red), green: \(green), blue: \(blue), alpha: \(alpha)"

When you use the word self, you are referring to the store property and not the parameter.

Good luck

You took off the self out of description, and not the ones I suggested on my code.

Please replace your code with mine.

self.description = "red: \(red), green: \(green), blue: \(blue), alpha: \(alpha)"

Should be red: (red), and NOT red: (self.red).