mvvm-composable-functions.swift

import UIKit

final class ViewController: UIViewController {
    
    @IBOutlet var incrementButton: UIButton!
    @IBOutlet var totalCount: UILabel!
    
    var viewModel = ViewModel()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Here, I am explicitly putting `Self` in a Closure
        // This is a Strong Reference
        // You are free to make it into a weak reference, or either clear the ViewModel's properties to free it of holding reference to this ViewController
        let incrementCountEffect: Effect<(count: Int, countLabel: String)> = { newCount in
            self.totalCount.text = newCount.countLabel
        }
        viewModel.incrementCountEffect = incrementCountEffect
    }
    
    @IBAction func buttonTapped(_ sender: UIButton) {
        viewModel.incrementCount()
    }
    
}

typealias Effect<A> = ((A) -> ())

struct ViewModel {
    private(set) var currentCount: Int = 0
    
    var incrementCountEffect: Effect<(count: Int, countLabel: String)>? = nil
    
    private let countLabelString: (Int) -> String = { value -> String in
        return "Count is: \(value)"
    }
    
    mutating func incrementCount() {
        currentCount += 1
        let countLabel = countLabelString(currentCount)
        incrementCountEffect?((count: currentCount, countLabel: countLabel))
    }
    
    
    // Call this method to dereference closures held by this object
    mutating func dereference() {
        incrementCountEffect = nil
    }