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iOS

Janson Roberts
Janson Roberts
5,071 Points
Posted by Janson Roberts
Janson Roberts
5,071 Points

Custom Initializers RGB

I'm told the following instructions:

In the editor, I've declared a struct named RGBColor that models a color object in the RGB space.

Your task is to write a custom initializer method for the object. Using the initializer, assign values to the first four properties. Using the values assigned to those properties, create a value for the description property that is a string representation of the color object.

For example, given the values 86.0 for red, 191.0 for green, 131.0 for blue, and 1.0 for alpha, each of the stored properties should hold these values and the description property should look like this:

"red: 86.0, green: 191.0, blue: 131.0, alpha, 1.0"

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){
    self.red = 86.0
    self.green = 191.0
    self.blue = 131.0
    self.alpha = 1.0
    self.description = "red: \(self.red), green: \(self.green), blue: \(self.blue), alpha: \(self.alpha)"
  }
}

I think I pretty much have it correct, but I keep getting errors! Either it tells me not to use the memberwise default, or it tells me to make sure the string I'm assigning the description property matches the example. Is there something clear that I'm missing here???

3 Answers

Steve Hunter
Steve Hunter
57,712 Points
Steve Hunter
Steve Hunter
57,712 Points

Hi Janson,

The init method receives the values for the first four stored properties. Don't then hard-code them inside init. You want to say self.red = red etc.

You can then use the passed-in values inside the string, rather than accessing the self ones. But give both a try.

If that still doesn't fix it, copy a link to the challenge in here and I'll go through it properly.

Steve.

Janson Roberts
Janson Roberts
5,071 Points
Janson Roberts
Janson Roberts
5,071 Points

Here's what I changed. I'm still not sure how I'm supposed to get back the double values if there's nowhere to input them???

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){
    self.red = red
    self.green = green
    self.blue = blue
    self.alpha = alpha
    self.description = "red: \(self.red), green: \(self.green), blue: \(self.blue), alpha: \(self.alpha)"
  }
}
Steve Hunter
Steve Hunter
57,712 Points

Hi there,

You're correct with that code - it should pass the challenge.

The struct is used by someone wanting to create their own specific RGB color. They would call the struct and pass in their chosen values to create a color. The init method is called when a struct is created so, on creation, the values are required. The values given in the question are just example ones - they aren't needing to be input anywhere.

A new color can be created with:

let myColor = RGBColor(red: 123.4, green: 12.34, blue: 34.5, alpha: 0.5)

// or other values:

let yourColor = RGBColor(red: 3.4, green: 112.34, blue: 44.5, alpha: 0.6)

But the challenge doesn't need a color to be created - it just wants the struct completing.

Steve.

Janson Roberts
Janson Roberts
5,071 Points
Janson Roberts
Janson Roberts
5,071 Points

Thanks, Steve.

Right now, the code challenge is being unresponsive, so I'll take your word for it that this is correct. Perhaps I'll test it on the desktop later (currently using the app).

Steve Hunter
Steve Hunter
57,712 Points

Let me know how you get on.

Did you understand the point about the challenge not requiring values to be entered?

Steve.

Janson Roberts
Janson Roberts
5,071 Points
Janson Roberts
Janson Roberts
5,071 Points

Hey Steve,

I finally was able to login to the desktop version here in Safari and test out the code. Worked like a charm. =)

It makes sense little by little each day. I understand now (I think) that the struct RGBColor has stored properties that were pre-listed in the editor by the instructor. After that, the instructions state that I have to create a custom initializer method and pass in the parameters for RGB (they're all of type Double). After that, I have to list the stored properties before an instance of the custom init method can be called. This means that for each variable, I have to assign a stored property, and since we're calling from outside the init method, I have to use the dot syntax. After I'm finished listing the values for the stored properties for the init method, I need to also do the same for the description property (represented in a String, because it's of type String). Finally (this step isn't required), I could call an instance of the method outside the scope of the struct that will actually be where I pass in the values for the RGB Doubles. (86.0 and so on...) Am I correct?

Thanks so much for explaining!

Steve Hunter
Steve Hunter
57,712 Points

Hi Janson,

Yes, you pretty much have that down.

A struct contains stored properties. The init method is called when an instance of the struct is required by the user/coder. The init method must assign a value to all stored properties. Some of these values can be received by the init method; in this case the red, green, blue and alpha values are received by init, i.e. they are passed in by the user. The description property is also assigned by the init method but its value is not passed into the method.

The assignment inside the init method (also known as a constructor in most other languages because that's what it does!) uses dot notation and the concept of self. This is used to distinguish between the stored property, such as red, and the passed-in value, also called red. In Xcode, you can probably get away without using self as long as you click on the correct version of red but that's poor form and makes for unclear code - Java uses a similar way of distinguishing between these two variables but uses the keyword this instead of self. Same difference.

And, yes, you would create your instance of an RGBColor by creating a new variable/constant to store it, then passing in the four required parameters into the RGBColor() call. You would then be able to access all the stored properties, again, using dot notation. Using my example above, myColor, accessing those properties would look like:

let redValue = myColor.red // redValue will hold 123.4
let greenValue = myColor.green // greenValue holds 12.34

let colorString = myColor.description // you get the idea! :-)

I hope that helps.

Steve.