Swift

class LoginViewController: UIViewController {
//Class 'LoginViewController' has no initializers
    
    private var loginButton: UIButton
    
    override func viewDidLoad() {
        super.viewDidLoad()
        loginButton = UIButton(frame: CGRect(x: 0, y: 0, width: 100, height: 36))
        view.addSubview(loginButton)
    }
}

Kotlin

class LoginFragment : Fragment() {
 
    private lateinit var loginButton: Button
 
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        loginButton = view.findViewById(R.id.login_button)
    }
}
 

Swift

class LoginViewController: UIViewController {
 
    @Lateinit private var loginButton: UIButton
 
    override func viewDidLoad() {
        super.viewDidLoad()
        loginButton = UIButton(frame: CGRect(x: 0, y: 0, width: 100, height: 36))
        view.addSubview(loginButton)
    }
}

Implemente lateinit in Swift

@propertyWrapper
struct Lateinit<T> {
    private var _value: T?
    var wrappedValue: T {
        get {
            guard let value = _value else {
                fatalError("Lateinit property has not been initialized")
            }
            return value
        }
        set { _value = newValue }
    }
}

Duplicate coding

acceptButton.setBackgroundColor(SplashGDPRColors.acceptButton.value, for: .normal)
acceptButton.setTitleColor(.white, for: .normal)
acceptButton.setTitle(String(PG_gdprContinue), for: .normal)
acceptButton.clipsToBounds = true
acceptButton.layer.cornerRadius = 3
acceptButton.isEnabled = true

withObject(acceptButton) {
    $0.setBackgroundColor(SplashGDPRColors.acceptButton.value, for: .normal)
    $0.setTitleColor(.white, for: .normal)
    $0.setTitle(String(PG_gdprContinue), for: .normal)
    $0.clipsToBounds = true
    $0.layer.cornerRadius = 3
    $0.isEnabled = true
}

Redundant variable and statement

let row = itemArray.firstIndex {
    $0.type == .tool 
}
 
if let row = row {
    let indexPath = IndexPath(row: row, section: 0)
    if let toolCell = tableView.cellForRow(at: indexPath) as? MainPageToolCell {
        toolCell.refreshDraftsEntrance()
    }
}

itemArray.firstIndex {
    $0.type == .tool
}?.let { //$0: Int
    IndexPath(row: $0, section: 0)
}.let { //$0: IndexPath
    tableView.cellForRow(at: $0) as? MainPageToolCell
}?.also { //$0: MainPageToolCell
    $0.refreshDraftsEntrance()
}

Functional programming!

Kotlin

The Kotlin standard library contains several functions:

let, run, with, apply, and also

Kotlin

Kotlin

Context object: this or it

val str = "Hello"
// this
str.run {
    println("The string's length: $length")
    //println("The string's length: ${this.length}") // does the same
}
 
// it
str.let {
    println("The string's length is ${it.length}")
}

Kotlin

with

//with
val book = Book()
val privce = with(book) {
    name = "Scope Functions"
    price = 400
    price
}

Kotlin

also & apply

//apply
val book = Book().apply {
    name = "Scope Functions"
    price = 400
}
 
//also
val book = Book().also {
    it.name = "Scope Functions"
    it.price = 400
}

Swift

Can the context be changed in Swift?

Swift

let & also

//let
let price: Int = Book().let {
    $0.name = "Scope Functions"
    $0.price = 400
    $0.price
}

//also
let bool = Book().also {
    $0.name = "Scope Functions"
    $0.price = 400
}

Swift

with

//withStruct
let book: Book = ...
let price: Int = with(book) {
    book.checked = true
    return book.price
}

Implement scope functions in Swift

@inlinable
public func withStruct<T: Any, V>(_ value: T, _ block: (inout T) throws -> V) rethrows -> V {
    var copy = value
    return try block(&copy)
}

@inlinable
@discardableResult public func withObject<T: AnyObject, V>(_ value: T, _ block: (T) throws -> V) rethrows -> V {
    return try block(value)
}

extension ScopeFunction where Self: Any {
    @inlinable
    @discardableResult public func `let`<T>(_ block: (inout Self) throws -> T) rethrows -> T {
        var copy = self
        return try block(&copy)
    }
 
    @inlinable
    public func also(_ block: (inout Self) throws -> Void) rethrows -> Self {
        var copy = self
        try block(&copy)
        return copy
    }  
}

let dic = [String: String]()
//dic.let { it -> [String: String] in
//dic.also { it -> [String: String] in
withStruct(dic) { it -> [String: String] in
    it["Name"] = "Allen"
    return it
}.also {
    print($0)
}
print("\(dic)")

var dic = [String: String]()
//assign the return value!
dic = withStruct(dic) { it -> [String: String] in
    it["Name"] = "Allen"
    return it
}.also {
    print($0)
}
print("\(dic)")