React like renderer concept for Swift

react.swift

import UIKit
import PlaygroundSupport



/**********************************************
 *             Library Types                  *
 **********************************************/
typealias REProps = [String: Any]

class REComponent {
    var children: [REComponent]
    var props: REProps
    var state: Any?

    required init(_ props: REProps, _ children: [REComponent] = []) {
        self.props = props
        self.children = children
        self.state = nil
    }

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



/**********************************************
 *           Built-in components              *
 **********************************************/
class RELabel: REComponent {
    override func toNativeView() -> UIView? {
        let view = UILabel()
        
        if props["backgroundColor"] != nil {
            view.backgroundColor = (props["backgroundColor"] as! UIColor)
        }
        
        if props["text"] != nil {
            view.text = (props["text"] as! String)
        }
        
        if props["textColor"] != nil {
            view.textColor = (props["textColor"] as! UIColor)
        }
        
        return view
    }
}

class REStack: REComponent {
    override func toNativeView() -> UIView? {
        let view = UIStackView()
        
        view.frame = CGRect(x: 0, y: 0, width: 200, height: 200)
        
        if props["alignment"] != nil {
            view.alignment = (props["alignment"] as! UIStackViewAlignment)
        }
        
        if props["axis"] != nil {
            view.axis = (props["axis"] as! UILayoutConstraintAxis)
        }
        
        if props["distribution"] != nil {
            view.distribution = (props["distribution"] as! UIStackViewDistribution)
        }
        
        for child in children {
            RE_render(node: child, toTargetView: view)
        }
        
        return view
    }
}



/**********************************************
 *           Rendering function               *
 **********************************************/
func RE_render(node: REComponent, 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": UIStackViewAlignment.center], [
            RELabel(["backgroundColor": UIColor.cyan, "text": "Hello:"]),
            RELabel(["textColor": UIColor.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()