SwiftLearning

New things i learn about swift programming language

Table Of Contents

1. Toupls
   
2. Higher Order Function
   
3. New way of handling getter setter
   
4. Closed Range Operator
   
5. init, failable init, convenience init
   
6. Computed Property
   
7. Property Wrapper
   
8. Associatedtype
   
9. Protocol Extention
   
10. Closure
    
11. Mutating Function
    
12. Lazy
    
13. where keyword
    
14. Error Handaling
    
15. Type Casting
    

Toupls

Tuples group multiple values into a single compound value. The values within a tuple can be of any type and don’t have to be of the same type as each other.

var httpError = (404, "Not Found")

print(httpError.0) // prints 404
print(httpError.1) // prints "Not Found"

var httpError2 = (statusCode: 404, message: "Not Found")

print(httpError2.statusCode) // prints 404
print(httpError2.message) // prints "Not Found"

let (statusCode, message) = httpError

print(statusCode) // prints 404
print(message) // prints "Not Found"

New way of handling getter setter

class Person {
    private var name: String
    private var age: Int
    
    init(name: String, age: Int){
        self.name = name
        self.age = age
    }
    
    func getName() -> String {
        return self.name
    }
}


let person = Person(name: "Person 1", age: 23)
print(person.getName())

class Person2 {
    private(set) var name: String
    private(set) var age: Int
    var salary: Int {
        get { return 2000}
    }
    
    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}


let person2 = Person2(name: "Person 2", age: 24)
//person2.name = "New Name"  // this will throw error
//person2.salary = 1000 // this will throw error coz salary is only getable 
print(person2.name)

Closed Range Operator

The closed range operator (a...b) defines a range that runs from a to b, and includes the values a and b. The value of a must not be greater than b.

for index in 1...5 {
  print("\(index) times 5 is \(index * 5)")
}

// this prints 
//1 times 5 is 5
//2 times 5 is 10
//3 times 5 is 15
//4 times 5 is 20
//5 times 5 is 25

Half Open Range Operator

The half-open range operator (a..<b) defines a range that runs from a to b, but doesn’t include b

for index in 1..<5 {
    print("At \(index)") // prints 1,2,3,4
}

One-Sided Range

let myArray = ["1", "2", "3", "4", "5"]

for item in  myArray[2...]{
    print(item)  // prints 3,4,5
}


for item in myArray[...2] {
    print(item) // prints 1,2,3
}

init , failable init, convenience init.

// Init 

struct Person {
    let name: String
    let age: Int
    let designation: String
}

let person = Person(name: "Perosn", age: 30, designation: "iOS Engineer")

struct Person2 {
    let name: String
    let age: Int
    let designation: String
    
    init(name: String, age: Int) {
        self.name = name
        self.age = age
        designation = ""
    }
}

let person2 = Person2(name: "Perosn 2", age: 30)

// failable init

struct Item {
    let name: String
    let price: Int
    let quantity: Int
    
    init?(name: String, price: Int, quantity: Int) {
        
        guard quantity < 0 else {
            return nil
        }
        
        self.name = name
        self.price = price
        self.quantity = quantity
    }
}

// convenience init

class Item2 {
    var name: String
    var price: Int
    var quantity: Int
    
    init(name: String, price: Int, quantity: Int) {
        self.name = name
        self.price = price
        self.quantity = quantity
    }
//
    init(name : String, price: Int) {
        self.name = name
        self.price = price
        self.quantity = 1
    }
    
    convenience init(name: String) {
        self.init(name: name, price : 1, quantity : 1)
    }
}

let item2 = Item2(name: "", price: 2)

Lazy

// lazy

struct Calculate {
    static func havyCalculation() -> Int{
        var mArray = [Int]()
        
        for item in 1...4000 {
            mArray.append(item)
        }
        
        return mArray.last!
    }
}

struct Person{
    let name: String
    let age: Int
    lazy var calculation = {
       return Calculate.havyCalculation()
    }()
    
    lazy var showPerson = {
        return "Name is \(name) , Age is \(age)"
    }()
}

var person = Person(name: "EA Rashel", age: 100)
print(person.showPerson) // Name is EA Rashel , Age is 100
print(person.calculation) // it will calculate first time and store it
print(person.calculation) // this time is will return the stored value

Computed property

Computed property are those which value are not set directly. We set the value by some calculation

struct Person{
    var monthlySalary: Int
    var yearlySalary : Int {
        get {
            return monthlySalary * 12
        }
    }
}

let person = Person(monthlySalary: 1000)
person.yearlySalary // this will return 120000

*** Computed property will calculate every time it is called. where as lazy property will calculate first time and store the value and return the value if called 2nd time.

*** Lazy is not thread safe

Property Wrapper

extension String {
    
    func isValidEmail()-> Bool {
        let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}"

         let emailPred = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
         return emailPred.evaluate(with: self)
    }
}


@propertyWrapper
struct EmailValidationWrapper {
    
    var value: String
    var wrappedValue: String {
       
        get{
            return isValidEmail(email: value) ? value : String()
        }
        
        set{
            value = newValue
        }
    }
    
    
    init(emailValue: String) {
        value = emailValue
    }
    
    
    private func isValidEmail(email: String) -> Bool {
        let emailRegEx = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}"

         let emailPred = NSPredicate(format:"SELF MATCHES %@", emailRegEx)
         return emailPred.evaluate(with: email)
    }
}


struct User {
    
    var name: String
    @EmailValidationWrapper var email: String
    
    
   private func validate() -> Bool {
        if name.isEmpty || email.isEmpty {
            return false
        }
        
        return true
    }
    
    
    func register() {
        
        if validate() {
            print("done register")
        }else {
            print("Error")
        }
    }
}


let user = User(name: "test", email: EmailValidationWrapper(emailValue: "test@gmail.com"))


// another example
@propertyWrapper
class Prefixer{
    
    var wrappedValue: Int
    var prefixer: String?
    var projectedValue: String {
        guard let prefixer = prefixer else {
            return"\(wrappedValue)"
        }
        
        return "\(prefixer)\(wrappedValue)"
    }
    
    init(prefixer: String? = nil ,defaultValue: Int = 0) {
        self.wrappedValue = defaultValue
        self.prefixer = prefixer
    }
}

class Product{
    var name: String
    @Prefixer(prefixer: "$") var price: Int
    
    init(name: String, price: Int){
        self.name = name
        self.price = price
    }
}

let item = Product(name: "Book", price: 22)

print(item.$price) // $price will return the projectedValue && price will return the wrappedValue



// use in userdefaults

@propertyWrapper
class UserSettings<T>{
    
    var defaults = UserDefaults.standard
    
    var wrappedValue: T {
        set { defaults.set(newValue, forKey: key) }
        get { defaults.value(forKey: key) as? T ?? defaultValue }
    }
    var defaultValue: T
    var key: String
    init(_ key: String,_ defaultValue: T) {
        self.key = key
        self.defaultValue = defaultValue
    }
}

struct Settings {
    @UserSettings("language", "en") var language: String
}

let settings  = Settings()
print(settings.language)  // en
settings.language = "bn"
print(settings.language) // bn

Associatedtype

struct Movie{
    let name:String
}

struct User {
    let firstname:String
}


protocol WebService: class {
    
    associatedtype Model
    
    func getAll(url: URL, completion: (Result<Model, Error>) -> Void)
    
}


class MovieService: WebService {
    typealias Model = Movie
    
    func getAll(url: URL, completion: (Result<Movie, Error>) -> Void) {
        
    }
}


class UserService: WebService {
    
    func getAll(url: URL, completion: (Result<User, Error>) -> Void) {
        
    }
}

Protocol Extention

protocol Styling{
    func changeColor()
}

extension Styling {
    func changeColor() {
        print("Changed color to WHITE")
    }
}

class MyButton: Styling  {
    
}

class MyTextField: Styling {
    func changeColor() {
        print("Changed color to RED")
    }
}

let button = MyButton()
button.changeColor() // will print default value WHITE
let textField = MyTextField()
textField.changeColor() // will print overridien value RED

Generic Protocol with associatetype

protocol MyGenericProtocol{
    associatedtype InputType
    associatedtype ReturnType
    
    func multiply(value: InputType) -> ReturnType
}

class Test1: MyGenericProtocol {
    
    typealias InputType = Int
    typealias ReturnType = Int
    
    func multiply(value: Int) -> Int {
        return value * value
    }
}

class Test2: MyGenericProtocol {
    func multiply(value: Int) -> Int {
        return value * value
    }
}

Higher Order Function

Map & CompactMap

struct User{
    let name: String
    let age: Int
}

let users = [
    User(name: "User 1", age: 20),
    User(name: "User 2", age: 30),
    User(name: "User 3", age: 40)
]

//let userNames = users.map { (user) -> String in
//    return user.name
//}

let userNames = users.map { $0.name }


print(userNames)

let values = ["1", "two", "3", "four", "5"]

let intValues = values.map{ Int($0) } // accept nil value
print(intValues)
let intValuesWithoutNil = values.compactMap{ Int($0) } // dont accept nil value
print(intValuesWithoutNil)

Closure

// closure
func addition(num1: Int, num2: Int) -> Int{
    return num1 + num2
}

var addTwoNumber = addition


let add = addition(num1: 10, num2: 30)
print(add)

let add1 = addTwoNumber(10,30)
print(add1)


var addTwoNumber2: (Int, Int) -> Int = {
    (num1, num2) in
    return num1 + num2
}

let add2 = addTwoNumber2(20,20)
print(add2)

var addTwoNumber3: (Int, Int) -> Int = {
    return $0 + $1
}

let add3 = addTwoNumber3(20,20)
print(add3)

Function Call Sequence in closure

// function call sequence in closure

func printGoodMorningMessage(isMorning: Bool, name: String){
    
    if isMorning {
        print("Good Morning \(name)")
    }
}

//printGoodMorningMessage(isMorning: true, name: "EA Rashel") // this will print Good morning message
//printGoodMorningMessage(isMorning: false, name: "Mark Zugarburg") // this will print nothing

func assignName(name: String) -> String {
    print("assign name \(name)")
    return name
}

//printGoodMorningMessage(isMorning: true, name: assignName(name: "EA Rashel 2"))
//printGoodMorningMessage(isMorning: false, name: assignName(name: "Mark Zugarburg 2"))

/**
 this is the output for above code
 
 assign name EA Rashel 2
 Good Morning EA Rashel 2
 assign name Mark Zugarburg 2
 */

func printGoodMorningMessage2(isMorning : Bool, name: () -> String ){
    
    if isMorning {
        print("Good Morning 2 \(name())")
    }
}


printGoodMorningMessage2(isMorning: true) { () -> String in
    return assignName(name: "EA Rashel 3")
}


printGoodMorningMessage2(isMorning: false) { () -> String in
    return assignName(name: "Mark Zugarburg 3")
}

/**
 this is the output for above code
 
 assign name EA Rashel 3
 Good Morning EA Rashel 3
 */

Mutating Function

class Test{
    
    var items = [Int]()
    
    func push(value: Int) {
        items.append(value)
    }
    
    func pop() -> Int? {
        if !items.isEmpty {
            return items.removeLast()
        }
        return nil
    }
}

// struct values are immutable by default
// to chnage its value we need to make it mutable first
struct TestMutating {
    
    var items = [Int]()
    
    mutating func push(value: Int) {
        items.append(value)
    }
    
    mutating func pop () -> Int? {
        
        if !items.isEmpty {
            return items.removeLast()
        }
        
        return nil
    }
}

var mutate = TestMutating(items: [1,2,3,4])
mutate.pop()
mutate.push(value: 5)

where keyword

// where
// where is a powerful keyword in swift to easily filter out value.
// usage of where

// in enums

enum Action{
    case createUser(age: Int)
    case createPost
}

func createAction(action: Action) {
    switch action {
    case .createUser(let age) where age < 30:
        print("User is young")
    case .createUser:
        print("User is aged")
    default:
        print("Default")

    }
}

createAction(action: .createUser(age: 20)) // User is young
createAction(action: .createUser(age: 40)) // User is aged

// in for-loop. printing even numbers

let items = [0,1,2,3,4,5,6,7,8,9,10]

for item in items where item % 2 == 0 {
    print(item) // 0 ,2, 4, 6, 8, 10
}


// in protocol extention

extension Array where Element == Int {
    func printAvgNumber() {
        let total = reduce(0, +)
        let avg  = total / count
        print("Avg is : \(avg)")
    }
}

items.printAvgNumber() // 5

// in first

let names = ["john", "adam", "jerry", "alan"]

let firstAName = names.first { (name) -> Bool in
    return name.first == "a"
}

print(firstAName) // adam

let cehckIfAdamExists = names.contains (where: { (name) -> Bool in
    return name == "adam"
})

print(cehckIfAdamExists) // true

Error handaling

enum CustomError: Error {
    case NameFieldEmpty(msg: String)
    case PhoneFieldEmpty(msg: String)
    case TestError
}

func createUser(name: String, phone: String) throws {
    if name.isEmpty {
        throw CustomError.NameFieldEmpty(msg: "Name field is empty")
    }
    
    if phone.isEmpty{
        throw CustomError.PhoneFieldEmpty(msg: "Phone Field is empty")
    }
    
    print("User Created. Name \(name)")
}

do {
    try createUser(name: "asda", phone: "asdasd")
}catch CustomError.NameFieldEmpty(let msg) {
    print(msg)
}catch CustomError.PhoneFieldEmpty(let msg) {
    print(msg)
} catch is CustomError{
    print("Other error")
} catch (_) {
    print("No Custom Error.")
}

Type Casting

Type casting in Swift is implemented with the is and as operators. These two operators provide a simple and expressive way to check the type of a value or cast a value to a different type.

class MediaItem{
    var name: String
    init(name: String) {
        self.name = name
    }
}

class MovieItem: MediaItem{
    var director: String
    
    init(name: String, director: String) {
        self.director = director
        super.init(name: name)
    }
}

class SongItem: MediaItem {
    var artist: String
    init(name: String, artist: String) {
        self.artist = artist
        super.init(name: name)
    }
}

let library = [
    MovieItem(name: "Movie 1", director: "Director 1"),
    SongItem(name: "Song 1", artist: "Artist 1"),
    MovieItem(name: "Movie 2", director: "Director 2")
]

var movieItemCount = 0
var songItemCount = 0

// type checking
for item  in library {
    if item is MovieItem {
        movieItemCount += 1
    }else if item is SongItem {
        songItemCount += 1
    }
}

print("Movie item count = \(movieItemCount) , Song item count = \(songItemCount)") // Movie item count = 2 , Song item count = 1

// downcasting

for item in library {
    if let movie = item as? MovieItem {
        print("Director: \(movie.director)")
    }else if let song = item as? SongItem {
        print("Artist : \(song.artist)")
    }
}

/**
    Director: Director 1
    Artist : Artist 1
    Director: Director 2
**/

Useful Links

1. Swift Documentation
2. Code Cat Swift tutorial
3. Best Resources for Advanced iOS developer
4. Avander lee (swiftlee)