CachingPlayground.swift

import UIKit
import PlaygroundSupport

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

        let label = UILabel()
        label.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
        label.text = "Hello World!"
        label.textColor = .black
        
        view.addSubview(label)

        let button = UIButton()
        button.frame = CGRect(x: 150, y: 240, width: 200, height: 20)
        button.setTitle("Fetch", for: .normal)
        button.backgroundColor = .systemBlue
        button.addTarget(self, action: #selector(fetchAction), for: .touchUpInside)

        view.addSubview(button)
        self.view = view
    }

    @objc func fetchAction() {
        print()
        fetch(title: "useProtocolCachePolicy", policy: .useProtocolCachePolicy)
        fetch(title: "returnCacheDataElseLoad", policy: .returnCacheDataElseLoad)
        fetch(title: "reloadIgnoringLocalCacheData", policy: .reloadIgnoringLocalCacheData)
        fetch(title: "reloadRevalidatingCacheData", policy: .reloadRevalidatingCacheData)
    }

    func fetch(title: String, policy: NSURLRequest.CachePolicy) {
        let configuration = URLSessionConfiguration.default
        configuration.requestCachePolicy = policy
        let urlSession = URLSession(configuration: configuration)

        var request = URLRequest(url: URL(string: "http://localhost:3000")!)
        request.cachePolicy = policy
        urlSession.dataTask(with: request) { data, response, error in
            guard let data = data else { return }
            print(title, String(data: data, encoding: .utf8)!)
        }.resume()
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()
PlaygroundPage.current.needsIndefiniteExecution = true