Swift cheatsheet

var greeting: String = "Hello"
var numberOfToys: Int = 8
var isMorning: Bool = true
var price: Double = 8.99

var apples = 6
print("I have \(apples) apples!")

// print: I have 6 apples!

let myLongString = """
Swift?
This is my favorite language!
Yeah!
"""

// This line represents a comment in Swift.

/*
This is all commented out.
None will run!
*/

let player = (name: "Maya", level: 5)
let (currentName, curLevel) = player
print("\(currentName): level \(curLevel)")
// print: Maya: level 5

// MARK: -view settings

MARK can be used to display comments in the column

// TODO: update logic to accommodate data changes

TODO is used to display reminders of things that need to be done

// FIXME: Fix buggy behavior when making changes to existing entries

FIXME is used to display reminders about things that need to be fixed

Variables are declared with var:

var greeting = "Hello"
var numberOfToys = 8
var isMorning = true

For clarity, variable declarations can contain type annotations:

var greeting: String = "Hello"
var numberOfToys: Int = 8
var isMorning: Bool = true

Variables are mutable. Their values be changed:

var numberOfToys: Int = 8
numberOfToys += 1

print(numberOfToys)
// print "9"

Constants are declared with let:

let greeting = "Hello"
let numberOfToys = 8
let isMorning = true

For clarity, constant declarations can contain type annotations:

let greeting: String = "Hello"
let numberOfToys: Int = 8
let isMorning: Bool = true

Constants are immutable. Their values be changed:

let numberOfToys: Int = 8
numberOfToys += 1
// Error: numberOfToys is immutable

var distance = 5 {
  didSet {
    print("The distance is set to \(distance)")
    print("Its old value is: \(oldValue)")
  }
}
distance = 10 // print: distance will be set to 10
              // print: its old value is: 5

var distance = 5 {
  willSet(newDistance) {
    print("The distance will be set to \(newDistance)")
  }
  didSet {
    print("The distance is set to \(distance)")
    print("Its old value is: \(oldValue)")
  }
}
distance = 10

var halloween = true
if halloween {
  print("Trick or treat!")
}
// print: Trick or treat!
if 5 > 3 {
  print("5 is greater than 3")
} else {
  print("5 is not more than 3")
}
// output: "5 is greater than 3"

var turbulence = false

if turbulence {
  print("Please sit down.")
} else {
  print("You are free to move around.")
}
// print: You are free to move around.

var weather = "rainy"
if weather == "sunny" {
  print("Get some sunscreen")
} else if weather == "rainy" {
  print("Take an umbrella")
} else if weather == "snowing" {
  print("Put on your snow boots")
} else {
  print("Invalid weather")
}
// print: take an umbrella

5 > 1      // true
6 < 10     // true
2 >= 3     // false
3 <= 5     // true
"A" == "a" // false
"B" != "b" // true

-< less than -> greater than -<= less than or equal to ->= greater than or equal to -== is equal to -!= is not equal to

var driverLicense = true

driverLicense
    ? print("driver seat") : print("passenger seat")
// print: driver's seat

var secondaryColor = "green"

switch secondaryColor {
  case "orange":
    print("A mixture of red and yellow")
  case "purple":
    print("A mix of red and blue")
  default:
    print("This may not be a secondary color")
}
// print: mix of blue and yellow

let year = 1905
var artPeriod: String

switch year {
  case 1860...1885:
    artPeriod = "Impressionism"
  case 1886...1910:
    artPeriod = "Post-Impressionism"
  default:
    artPeriod = "Unknown"
}
// print: post-impressionism

let service = "Seamless"

switch service {
case "Uber", "Lyft":
    print("travel")
  case "DoorDash", "Seamless", "GrubHub":
    print("Restaurant delivery")
  case "Instacart", "FreshDirect":
    print("Grocery Delivery")
  default:
    print("Unknown service")
}
// print: restaurant takeaway

let num = 7

switch num {
  case let x where x % 2 == 0:
    print("\(num) is even")
  case let x where x % 2 == 1:
    print("\(num) odd number")
  default:
    print("\(num) is invalid")
}

// print: 7 odd

!true  // false
!false //true

true && true   // true
true && false  // false
false && true  // false
false && false // false

true || true   // true
true || false  // true
false || true  // true
false || false // false

!false && true || false // true

!false && true first evaluates and returns true Then, the expression, true || false evaluates and returns the final result true

false || true && false // false

true && false first evaluates to return false Then, the expression, false || false evaluates and returns the final result false

// without parentheses:
true || true && false || false
//----> true

// with brackets:
(true || true) && (false || false)
//----> false

func greet(name: String?) {
  guard let unwrapped = name else {
    print("Hello guest!")
    return
  }
  print("Hello \(unwrapped)!")
}
greet(name: "Asma") // output: Hello Asma!
greet(name: nil)    // output: Hello guest!

let zeroToThree = 0...3
//zeroToThree: 0, 1, 2, 3

for oddNum in stride(from: 1, to: 5, by: 2) {
  print(oddNum)
}
// print: 1
// print: 3

for char in "hehe" {
  print(char)
}
// print: h
// print: e
// print: h
// print: e

for num in 0...5 {
  if num % 2 == 0 {
    continue
  }
  print(num)
}
// print: 1
// print: 3
// print: 5

The continue keyword will force the loop to continue for the next iteration

for char in "supercalifragilistic" {
if char == "c" {
    break
  }
  print(char)
}
// print: s
// print: u
// print: p
// print: e
// print: r

for _ in 1...3 {
  print("Ole")
}
// print: Ole
// print: Ole
// print: Ole

var counter = 1
var stopNum = Int. random(in: 1...10)

while counter < stopNum {
  print(counter)
  counter += 1
}
// loop to print until the stop condition is met

A while loop accepts a condition and keeps executing its body code while the provided condition is true. If the condition is never false, the loop will keep running and the program will get stuck in an infinite loop

var scores = [Int]()
// array is empty: []

var grocery = ["🥓", "🥞", "🍪", "🥛", "🍊"]
print(grocery.count)
// print: 5

// use type inference:
var snowfall = [2.4, 3.6, 3.4, 1.8, 0.0]
// explicit type:
var temp: [Int] = [33, 31, 30, 38, 44]

var gymBadges = ["Boulder", "Cascade"]
gymBadges.append("Thunder")
gymBadges += ["Rainbow", "Soul"]
// ["Boulder", "Cascade", "Thunder",
// "Rainbow", "Soul"]

var moon = ["🌖", "🌗", "🌘", "🌑"]
moon.insert("🌕", at: 0)
// ["🌕", "🌖", "🌗", "🌘", "🌑"]

moon. remove(at: 4)
// ["🌕", "🌖", "🌗", "🌘"]

var employees = ["Peter", "Denial", "Jame"]
for person in employees {
  print(person)
}
// print: Peter
// print: Denial
// print: Jam

var paintingsInMOMA: Set = [
  "The Dream",
  "The Starry Night",
  "The False Mirror"
]

We can use a collection (Set) to store unique elements of the same data type

var team = Set<String>()

print(team)
// print: [] 

var vowels: Set = ["a", "e", "i", "o","u"]

To create a set filled with values, use the Set keyword before the assignment operator.

var cookieJar: Set = [
  "Chocolate Chip",
  "Oatmeal Raisin"
]
// add a new element
cookieJar.insert("Peanut Butter Chip")

var oddNumbers: Set = [1, 2, 3, 5]

// remove existing element
oddNumbers.remove(2)
// remove all elements
oddNumbers.removeAll()

var names: Set = ["Rosa", "Doug", "Waldo"]
print(names.contains("Lola")) // print: false

if names.contains("Waldo"){
  print("There's Waldo!")
} else {
  print("Where's Waldo?")
}
// print: There's Waldo!

var recipe: Set = ["Egg", "Flour", "Sugar"]

for ingredient in recipe {
  print ("Include \(ingredient) in the recipe")
}

var emptySet = Set<String>()
print(emptySet.isEmpty)     // print: true

var populatedSet: Set = [1, 2, 3]
print(populatedSet.isEmpty) // print: false

var band: Set = ["Peter", "Denial", "Jame"]

print("The band has \(band.count) players.")
// print: Band has 4 players.

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]

var setC = setA.intersection(setB)
print(setC) // print: ["D", "C"]

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]

var setC = setA.union(setB)
print(setC) 
// print: ["B", "A", "D", "F", "C", "E"]

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]

var setC = setA.symmetricDifference(setB)
print(setC)
// print: ["B", "E", "F", "A"]

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D"]

var setC = setA.subtracting(setB)
print(setC) 
// print: ["B", "A"]

var dictionaryName = [
  "Key1": "Value1",
  "Key2": "Value2",
  "Key3": "Value3"
]

An unordered collection of pairs of data or key-value pairs

var fruitStand = [
  "Coconuts": 12,
  "Pineapples": 12,
  "Papaya": 12
]

Each key is unique even if they all contain the same value

var numberOfSides = [
  "triangle": 3,
  "square": 4,
  "rectangle": 4
]

Contains only String keys and Int values

var employeeID = [
  "Hamlet": 1367,
  "Horatio": 8261,
  "Ophelia": 9318
]

// initializer syntax:
var yearlyFishPopulation = [Int: Int]()

// Empty dictionary literal syntax:
var yearlyBirdPopulation: [Int: Int] = [:]

var pronunciation = [
  "library": "lai·breh·ree",
  "apple": "a·pl"
]
// new key: "programming", new value: "prow gra"
pronunciation["programming"] = "prow·gra"

var bakery = [String:Int]()

// check if the dictionary is empty
print(bakery.isEmpty) // prints true
bakery["Cupcakes"] = 12
// check if the dictionary is empty
print(bakery.isEmpty) // print false

var fruitStand = [
  "Apples": 12,
  "Oranges", 17
]
print(fruitStand.count) // print: 2

var hex = [
  "red": "#ff0000",
  "yellow": "#ffff00",
  "blue": "#0000ff",
]

print("Blue hexadecimal code \(hex["blue"])")
// print: blue hex code Optional("#0000ff")

if let redHex = hex["red"] {
  print("red hexadecimal code \(redHex)")
}
// print: red hex code #ff0000

Assigning the value of a key-value pair to a variable will return an optional value. To extract values, use the optional expansion

var emojiMeaning = [
  "🤔": "Thinking Face",
  "😪": "Sleepy Face",
  "😵": "Dizzy Face"
]
// loop through keys and values
for (emoji, meaning) in emojiMeaning {
  print("\(emoji) is called '\(meaning)Emoji'")
}
// iterate through keys only
for emoji in emojiMeaning. keys {
  print(emoji)
}
// iterate through values only
for meaning in emojiMeaning. values {
  print(meaning)
}

func washCar() -> Void {
  print("Soap")
  print("Scrub")
  print("Rinse")
  print("Dry")
}

func greetLearner() {
 print("Welcome to QuickRef.ME!")
}
// function call:
greetLearner()
// print: Welcome to QuickRef.ME!

let birthYear = 1994
var currentYear = 2020

func findAge() -> Int {
  return currentYear-birthYear
}

print(findAge()) // prints: 26

func findDiff(_ a: Int, b: Int) -> Int {
  return a -b
}

print(findDiff(6, b: 4)) // prints: 2

func findSquarePerimet(side: Int) -> Int {
  return side *4
}

let perimeter = findSquarePerimet(side: 5)
print(perimeter) // print: 20

// Parameter: side
// Argument: 5

func nextTotalSolarEclipse() -> String {
  "April 8th, 2024 🌎"
}

print(nextTotalSolarEclipse())
// print: April 8th, 2024 🌎

func greet(person: String = "guest") {
  print("Hello \(person)")
}
greet() // Hello guest
greet(person: "Aliya") // Hello Aliya

func totalStudent(data: String...) -> Int {
  let numStudents = data.count
  return numStudents
}

print(totalStudent(data: "Denial", "Peter"))
// print: 2

func getFirstInitial(from name: String?) -> String? {
  return name?.first
}

Functions can accept optional types and return optional types. When a function cannot return a reasonable instance of the requested type, it should return nil

struct Building {
  var address: String
  var floors: Int
  init(address: String, floors: Int) {
    self.address = address
    self. floors = floors
  }
}

Structs or structs are used to programmatically represent real-life objects in code. A structure is created using the struct keyword, followed by its name, followed by a body containing its properties and methods

struct Car {
  var numOfWheels = 4
  var topSpeed = 80
}

var reliantRobin = Car(numOfWheels: 3)

print(reliantRobin.numOfWheels) // prints: 3
print(reliantRobin.topSpeed)    // print: 80

struct Person {
  var name: String
  var age: Int

  init(name: String, age: Int) {
    self.name = name
    self. age = age
  }
}

// Person instance:
var morty = Person(name: "Peter", age: 14)

print(type(of: "abc")) // print: String
print(type(of: 123))   // print: 123

struct Dog {
  func bark() {
    print("Woof")
  }
}
let fido = Dog()
fido.bark() // prints: Woof

class Person {
  var name = ""
  var age = 0
}

var sonny = Person()
// sonny is now an instance of Person

var ferris = Student()

ferris.name = "Ferris Bueller"
ferris.year = 12
ferris.gpa = 3.81
ferris.honors = false

use data type

class Student {
  var name: String
  var year: Int
  var gpa: Double
  var honors: Bool
}

Use default property values

class Student {
  var name = ""
  var gpa = 0.0
  var honors = false
}

struct Resolution {
  var width = 0
  var height = 0
}
class VideoMode {
  var resolution = Resolution()
  var interlaced = false
  var frameRate = 0.0
  var name: String?
}

The Resolution structure definition and the VideoMode class definition only describe the appearance of Resolution or VideoMode, create an instance of the structure or class:

let resolution = Resolution(width: 1920)
let someVideoMode = VideoMode()

enum Day {
  case monday
  case tuesday
  case wednesday
  case thursday
  case friday
  case saturday
  case sunday
}

let casualWorkday: Day = .friday

enum Dessert {
  case cake(flavor: String)
  case vanillaIceCream(scoops: Int)
  case brownie
}

let customerOrder: Dessert = .cake(flavor: "Red Velvet")
switch customerOrder {
  case let .cake(flavor):
    print("You ordered a \(flavor) cake")
  case .brownie:
    print("You ordered a chocolate cake")
}
// prints: "You ordered a red velvet cake"

enum Season: CaseIterable {
  case winter
  case spring
  case summer
  case falls
}

for season in Season.allCases {
  print(season)
}

Add conformance to the CaseIterable protocol to access the allCases property, which returns an array of all cases of the enumeration

enum Beatle: String {
  case john paul george ringo
}

print("The Beatles are \(Beatle.john.rawValue).")
// print: The Beatles are john.

enum Dessert {
  case cake(flavor: String)
  case vanillaIceCream(scoops: Int)
  case brownie
}

let order: Dessert = .cake(flavor: "Red Velvet")

enum Hello: String {
  case english = "Hello"
  case japanese = "Hello!"
  case emoji = "👋"
}
let hello1 = Hello(rawValue: "Hello!")
let hello2 = Hello(rawValue: "Привет")
print(hello1) // Optional(Hello.japanese)
print(hello2) // nil

enum ShirtSize: String {
  case small = "S"
  case medium = "M"
  case large = "L"
  case extraLarge = "XL"
  var description: String {
    return "The size of this shirt is \(self.rawValue)"
  }
}