VojtaStavik

var heyJude = ""

for verse in 0..<4 {
  heyJude += "Hey Jude, don't "
  switch verse {
  case 0, 3: heyJude += "make it bad\nTake a sad song and make it better"
  case 1:    heyJude += "be afraid\nYou were made to go out and get her"
  case 2:    heyJude += "let me down\nYou have found her, now go and get her"
  default: fatalError()
  }

VojtaStavik

var vc1: UIViewController? = .init()
weak var weakVC1 = vc1
vc1 = nil
print(weakVC1 ?? "nil")

var vc2: UIViewController? = .init()
vc2?.loadViewIfNeeded() // Commenting this line out makes `weakVC2` nil, too.
weak var weakVC2 = vc2
vc2 = nil
print(weakVC2 ?? "nil")

VojtaStavik

class Object { }

var a: Object? = Object()
weak var weakA = a
a = nil
print(a ?? "nil")
print(weakA ?? "nil")

print("-------------------------------------------------")

VojtaStavik

import UIKit

enum UIKit { // UIKit namespace simulation
  enum Table { // The new "root" namespace for UITableView
    typealias View = UITableView
    typealias ViewController = UITableViewController
    typealias Cell = UITableViewCell
  }
}

VojtaStavik

import UIKit

class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

  @IBOutlet weak var tableView: UITableView!

  override func viewDidLoad() {
    super.viewDidLoad()
    NSLayoutConstraint.activate([
      tableView.topAnchor.constraint(equalTo: view.topAnchor),

VojtaStavik

+ (NSInteger) calculateHammingDistanceFor:(NSInteger)x and:(NSInteger)y {
    // Step 1: Find different bits
    NSUInteger differentBits = x ^ y;
    
    // Step 2: Count them
    NSUInteger counter = 0;
    while (differentBits > 0) {
        NSUInteger maskedBits = differentBits & 1;
        if (maskedBits != 0) {
            counter++;

VojtaStavik

func calculateHammingDistance(x: Int, y: Int) -> Int {
  
  // Step 1: Find different bits
  let signedDifferentBits = x ^ y
  
  // We bitcast Int to UInt to allow the algorithm work correctly also for negative numbers.
  var differentBits: UInt = unsafeBitCast(signedDifferentBits, to: UInt.self)
    
  // Step 2: Count them
  var counter = 0

VojtaStavik

  x & y   
  // Bitwise AND: Combines the bits of two numbers. 
  // It returns a new number whose bits are set to 1 only 
  // if the bits were equal to 1 in both input numbers
  
  Example:
       7 ==>  0 1 1 1
       3 ==>  0 0 1 1
       --------------
   7 & 3 ==>  0 0 1 1

VojtaStavik

  x >> a   
  // Bitwise shift: shifts all bits to the right of 'a' positions
  // (operator << to the left)
  Example:
         8 ==>  1 0 0 0
    8 >> 1 ==>  0 1 0 0
    8 >> 2 ==>  0 0 1 0
    8 >> 3 ==>  0 0 0 1
    8 >> 4 ==>  0 0 0 0

VojtaStavik

      2 ==>  0 1 0
      6 ==>  1 1 0
  ---------------- 
  2 ^ 6 ==>  1 0 0 // 100 in binary represents number 4