Intro to Dependency Diagrams and Composition

main.swift

import UIKit

class FeedViewController: UIViewController{
    var loadFeed: ((([String]) -> Void) -> Void)!
    
    convenience init(loadFeed: @escaping (([String]) -> Void) -> Void){
        self.init()
        self.loadFeed = loadFeed
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        loadFeed{ item in
            
        }
    }
}

import UIKit


protocol FeedLoader{
    func loadFeed(completion: @escaping ([String]) -> Void)
}

class FeedViewController: UIViewController{
    
    var loader: FeedLoader!
    
    
    convenience init(loader: FeedLoader){
        self.init()
        self.loader = loader
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        loader.loadFeed { items in
            
        }
    }
}


class RemoteFeedLoader: FeedLoader{
    func loadFeed(completion: @escaping ([String]) -> Void) {
        
    }
}

class LocalFeedLoader: FeedLoader{
    func loadFeed(completion: @escaping ([String]) -> Void) {
        
    }
}

class RemoteWithLocalFallbackFeedLoader: FeedLoader{
    let remote: RemoteFeedLoader
    let local: LocalFeedLoader
    
    init(remote: RemoteFeedLoader, local: LocalFeedLoader) {
        self.remote = remote
        self.local = local
    }
    
    func loadFeed(completion: @escaping ([String]) -> Void) {
        let load = Reachability.networkAvailable ? remote.loadFeed : local.loadFeed
        load(completion)
    }
}

struct Reachability{
    static let networkAvailable = false
}


let vc = FeedViewController(loader: RemoteFeedLoader())
let vc1 = FeedViewController(loader: LocalFeedLoader())
let vc2 = FeedViewController()
vc2.loader = RemoteWithLocalFallbackFeedLoader(remote: RemoteFeedLoader(), local: LocalFeedLoader())