Example of ``

sequence_state_next.swift

//: Playground - noun: a place where people can play

import UIKit
import CoreImage

enum Color: Int {
    case green = 1001
    case blue
    case black
    case yellow
}

extension Color: CustomStringConvertible {
    var description: String {
        var description: String
        switch self {
        case .green:
            description = "Green"
        case .blue:
            description = "Blue"
        case .black:
            description = "Black"
        case .yellow:
            description = "Yellow"
        }
        return description
    }
}

let greenView = UIView()
greenView.tag = Color.green.rawValue

let blueView = UIView()
blueView.tag = Color.blue.rawValue

let blackView = UIView()
blackView.tag = Color.black.rawValue

let yellowView = UIView()
yellowView.tag = Color.yellow.rawValue

yellowView.addSubview(blackView)
blackView.addSubview(blueView)
blueView.addSubview(greenView)

let seq = sequence(state: greenView) { (next: inout UIView) -> UIView? in
    let parent = next.superview
    next = parent != nil ? parent! : next
    return parent // The top most `parent` will be nil, stopping the execution of the closure
}

let greenColor = Color(rawValue: greenView.tag)!
var hierarchy = "\(greenColor)"
for v in seq {
    if let color = Color(rawValue: v.tag) {
        hierarchy += "->\(color)"
    }
}
print("hierarchy: \(hierarchy)") // hierarchy: Green->Blue->Black->Yellow