React like renderer concept for Swift

react.swift

import UIKit
import PlaygroundSupport



/**********************************************
 *             Library Types                  *
 **********************************************/
protocol REElement {
    func render() -> REElement?
    func toNativeView() -> UIView?
}

class REComponent<Props>: REElement {
    var children: [REElement]
    var props: [Props]
    var state: Any?

    init(_ props: [Props], _ children: [REElement] = []) {
        self.props = props
        self.children = children
        self.state = nil
    }

    func render() -> REElement? { return nil }
    func toNativeView() -> UIView? { return nil }
}



/**********************************************
 *           Built-in components              *
 **********************************************/
enum RELabelProps {
    case backgroundColor(UIColor)
    case text(String)
    case textColor(UIColor)
}

class RELabel: REComponent<RELabelProps> {
    override func toNativeView() -> UIView? {
        let view = UILabel()
        
        for prop in props {
            switch prop {
            case .backgroundColor(let value): view.backgroundColor = value
            case .text(let value): view.text = value
            case .textColor(let value): view.textColor = value
            }
        }
        
        return view
    }
}

enum REStackProps {
    case alignment(UIStackViewAlignment)
    case axis(UILayoutConstraintAxis)
    case distribution(UIStackViewDistribution)
}

class REStack: REComponent<REStackProps> {
    override func toNativeView() -> UIView? {
        let view = UIStackView()
        
        view.frame = CGRect(x: 0, y: 0, width: 200, height: 200)
        
        for prop in props {
            switch prop {
            case .alignment(let value): view.alignment = value
            case .axis(let value): view.axis = value
            case .distribution(let value): view.distribution = value
            }
        }
        
        for child in children {
            RE_render(node: child, toTargetView: view)
        }
        
        return view
    }
}



/**********************************************
 *           Rendering function               *
 **********************************************/
func RE_render(node: REElement, toTargetView targetView: UIView) {
    if let view = node.toNativeView() {
        if let stackedView = targetView as? UIStackView {
            stackedView.addArrangedSubview(view)
        } else {
            targetView.addSubview(view)
        }
        return
    }
    
    if let child = node.render() {
        RE_render(node: child, toTargetView: targetView)
        return
    }
}



/**********************************************
 *                User code                   *
 **********************************************/
class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        let tree = REStack([.alignment(.center)], [
            RELabel([.backgroundColor(.cyan), .text("Hello:")]),
            RELabel([.textColor(.blue), .text("World!")])
        ])

        RE_render(node: tree, toTargetView: view)

        self.view = view
    }
}

// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()