An approach for simplified wrapping of AppKit and UIKit view controllers in SwiftUI

SwiftUI WrappableViewController.swift

//
//  WrappableViewController.swift
//  macOS-Wordflower
//
//  Created by Marcus Westin on 1/24/20.
//  Copyright © 2020 Marcus Westin. All rights reserved.
//

// My preferred approach to wrapping AppKit and UIKit viewControllers in SwiftUI

import SwiftUI

protocol WrappableViewController: OSViewController {
    typealias ViewControllerType = Self
    typealias Context = OSViewControllerRepresentableContext<WrappedViewController<Self>>
    
    /// Optional: update view
    func update(context: Context)
    
    /// Optional: wrapped has a functional default implementation and should not
    /// have to be overriden by protocol implementations
    var wrapped: WrappedViewController<Self> { get }
}

// MARK: Default implementations
extension WrappableViewController {
    /// Default empty implementation of optional update function
    func update(context: Context) {}
    
    /// Implementation of wrapped, which should not be overriden by classes
    internal var wrapped: WrappedViewController<Self> {
        WrappedViewController { self }
    }
}

struct WrappedViewController<Wrappable: WrappableViewController>: OSViewControllerRepresentable {
    let wrap: () -> Wrappable
    
    internal func makeCoordinator() -> Wrappable {
        return wrap()
    }

    #if os(macOS)
    internal func makeNSViewController(context: NSViewControllerRepresentableContext<WrappedViewController<Wrappable>>) -> Wrappable.ViewControllerType {
        return context.coordinator
    }
    internal func updateNSViewController(_ view: Wrappable.ViewControllerType, context: NSViewControllerRepresentableContext<WrappedViewController<Wrappable>>) {
        context.coordinator.update(context: context)
    }

    #elseif os(iOS)
    internal func makeUIViewController(context: UIViewControllerRepresentableContext<WrapViewController>) -> Wrapper.ViewControllerType {
        return context.coordinator
    }
    internal func updateUIViewController(_ view: Wrapper.ViewControllerType, context: UIViewControllerRepresentableContext<WrapViewController>) {
        context.coordinator.update(context: context)
    }
    #endif
}


// MARK: - Example usage

struct WrappableViewController_Previews: PreviewProvider {
    static var previews: some View {
        Group {
            ExampleFirstResponderTextField().wrapped
            ExampleFirstResponderTextField().wrapped
        }
    }
    
    
    final class ExampleFirstResponderTextField: NSViewController, WrappableViewController, NSTextFieldDelegate {

        override func loadView() {
            let textField = NSTextField(frame: .zero)
            textField.stringValue = "Hello World!"
            self.view = textField
        }
    }
}