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iOS Object-Oriented Swift 2.0 Complex Data Structures Custom Initializers

Mike Sagafi
Mike Sagafi
2,128 Points
Posted by Mike Sagafi
Mike Sagafi
2,128 Points

I am at loss. The defined variables are constants. If I create a custom method then I can't update them

isn't this the way todo it?

struct RGBColor { let red: Double let green: Double let blue: Double let alpha: Double

let description: String

// Add your code below
init (red: Double, green: Double, blue: Double, alpha: Double, description: String) {
    self.red = red
    self.green = green
    self.blue = blue
    self.alpha = alpha
    self.description = "red: \(red), green: \(green), blue: \(blue), alpha: \(alpha)"
}

}

structs.swift 
struct RGBColor {
    let red: Double
    let green: Double
    let blue: Double
    let alpha: Double

    let description: String

    // Add your code below
    init (red: Double, green: Double, blue: Double, alpha: Double, description: String) {
        self.red = red
        self.green = green
        self.blue = blue
        self.alpha = alpha
        self.description = "red: \(red), green: \(green), blue: \(blue), alpha: \(alpha)"

    }
}

2 Answers

Joseph Kato
Joseph Kato
35,340 Points
Joseph Kato
Joseph Kato
35,340 Points

Hi Mike,

It looks like the issue is that your initializer method is expecting to be passed a value (that isn't actually used) for description:

init (red: Double, green: Double, blue: Double, alpha: Double, description: String) {

Consider the following example:

struct Point {
    let x: Int
    let y: Int

    let description: String

    init (x: Int, y: Int, description: String) {
        // Note: we don't use the `description` argument here...
        self.x = x
        self.y = y
        self.description = "x: \(x), y: \(y)"
    }
}

Given this definition of a Point, we can't create our own by simply passing values for x and y:

var myPoint = Point(x: 1, y: 2) // "ERROR: missing argument for parameter 'description' in call"

So, we'd have to do something like this:

var myPoint = Point(x: 1, y: 2, description: "this isn't used!")

But we don't want to have to do that every time, so we re-write our initializer method as:

init (x: Int, y: Int) {
    self.x = x
    self.y = y
    self.description = "x: \(x), y: \(y)"
 }
// We can now say `var myPoint = Point(x: 1, y: 2)`!
Florian Thompson
PLUS
Florian Thompson
Courses Plus Student 18,609 Points
Florian Thompson
Florian Thompson
Courses Plus Student 18,609 Points

Hi there,

your properties need to be declared as var in order for you to override them. You would go with let if you would give them an initial value.

if you want to avoid them to be modified you might want to change the access level. For example:

struct RGBColor {
   private var description: String
}

That way you can't change the value from outside the struct. If you would want to, you can write a helper method which needs to be marked as @mutating func

I hope this helped.