[Swift] NetworkManager Tutorial with a Singleton Class

NetworkManager.swift

import Foundation

enum API{
    static let baseURL = URL(string: "")
}

class NetworkManager {
    
    private static var sharedNetworkManager: NetworkManager = {
        
        let networkManager = NetworkManager(baseURL: API.baseURL!)
        return networkManager
    }()
    
    let baseURL: URL
    
    private init(baseURL: URL) {
        self.baseURL = baseURL
    }
    
    class func shared() -> NetworkManager {
        return sharedNetworkManager
    }
}