Dependency Injection

CodeSample.swift

import Foundation

class ViewController {
    var models: [String]!
    let networkLayer: NetworkLayer
    init(networkLayer: NetworkLayer) {
        self.networkLayer = networkLayer
    }
    
    func viewDidLoad() {
        models = networkLayer.request()
        debugPrint(models.count)
    }
}

class NetworkLayer {
    func request() -> [String] {
        // Example this is real network request
        return ["product1", "product2", "product3"]
    }
}

let networkLayer = NetworkLayer()
let viewController = ViewController(networkLayer: networkLayer)
viewController.viewDidLoad()