Swift, SwiftUI - .getRed(&red, green: &green, blue: &blue, alpha: &alpha) - swift

Question

I am following Stanfords' CS193p Developing Apps for iOS online course.
I'm trying to do the Assignment 6 Memorize.pdf.
It says to use this code below ⬇️, but it gives me always white color. Is there a bug somewhere? Please help.
import SwiftUI
struct RGBAColor: Codable, Equatable, Hashable {
let red: Double
let green: Double
let blue: Double
let alpha: Double
}
extension Color {
init(rgbaColor rgba: RGBAColor) {
self.init(.sRGB, red: rgba.red, green: rgba.green, blue: rgba.blue, opacity: rgba.alpha)
}
}
extension RGBAColor {
init(color: Color) {
var red: CGFloat = 0
var green: CGFloat = 0
var blue: CGFloat = 0
var alpha: CGFloat = 0
if let cgColor = color.cgColor {
UIColor(cgColor: cgColor).getRed(&red, green: &green, blue: &blue, alpha: &alpha)
}
self.init(red: Double(red), green: Double(green), blue: Double(blue), alpha: Double(alpha))
}
}
import SwiftUI
struct ContentView: View {
static let rgbaColorRed = RGBAColor(color: Color.red)
static let thisShouldBeRed = Color(rgbaColor: rgbaColorRed)
var body: some View {
Text("Hello, world!")
.padding()
.foregroundColor(ContentView.thisShouldBeRed) // why white here, not red???
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}

Answer 1

As the cgColor property's documentation says:
For a dynamic color, like one you load from an Asset Catalog using init(_:bundle:), or one you create from a dynamic UIKit or AppKit color, this property is nil.
Color.red is actually a dynamic color:
A context-dependent red color suitable for use in UI elements.
So Color.red.cgColor is nil, causing the getRed(_:green:blue:alpha:) call to not run, and the red, green, blue, alpha local variables remain 0. So the color you got is not "white", but "transparent".
You can actually create a UIColor directly from Color, without going through CGColor:
var red: CGFloat = 0
var green: CGFloat = 0
var blue: CGFloat = 0
var alpha: CGFloat = 0
// note here:
UIColor(color).getRed(&red, green: &green, blue: &blue, alpha: &alpha)
self.init(red: Double(red), green: Double(green), blue: Double(blue), alpha: Double(alpha))