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iOS Object-Oriented Swift 2.0 Complex Data Structures Custom Initializers

Rich Valiant
Rich Valiant
2,417 Points
Posted by Rich Valiant
Rich Valiant
2,417 Points

How to add a String of values to let description property?

I've watched each video in the series several times and I thought to create a method which returns a string and then add the result to the description variable but its a let property constant so I can't. I'm lost on how to accomplish this step. Any help would be appreciated.

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

    init(red: Double, green: Double, blue: Double, alpha: Double) {
      self.red = red
      self.green = green
      self.blue = blue
      self.alpha = alpha
    }

    let description: String

    // Add your code below

    func something() {
      self.description = "red: \(red), green: \(green), blue: \(blue), alpha \(alpha)"
      return description
    }
}

1 Answer

jcorum
jcorum
71,830 Points

Sergio, Hi! You need to create a custom initializer that gives a value to each of the 4 stored properties:

    init(red: Double, green: Double, blue: Double, alpha: Double) {
        self.red = red
        self.green = green
        self.blue = blue
        self.alpha = alpha
        description = "red: \(red), green: \(green), blue: \(blue), alpha: \(alpha)"
    }

Once the stored properties have a value, then description will as well, as it has access to the values stored in those properties.

So if you create a RGBColor object:

let color = RGBColor(red: 23/255, green: 235/255, blue: 155/255, alpha: 0.8)
print(color.description)

The value of red will be 23/255, ..., and description can use those values. What will be displayed (printed) in an Xcode playground will be this:

"red: 0.0901960784313725, green: 0.92156862745098, blue: 0.607843137254902, alpha: 0.8\n"
Rich Valiant
Rich Valiant
2,417 Points
Rich Valiant
Rich Valiant
2,417 Points

Hello jcorum,

Thank you so much. Very thorough explanation to the final print detail of color.description. Really illuminated it all in practice and in theory.

Got it!