HIDDEN GEMS IN SWIFT ! @JASDEV

IN OCTOBER 2015, I STARTED A TWITTER ACCOUNT CALLED @PUBLICEXTENSION

55 extensions so far 29 Playground pages GitHub

WHAT WE'LL COVER

> Literal convertible protocols > Experimental Operators > Apply mutating functions to immutable values > Attributes > Higher-level types for enum raw values > Metatypes > Custom pattern matching

LITERAL CONVERTIBLES > ArrayLiteralConvertible > BooleanLiteralConvertible > DictionaryLiteralConvertible > FloatLiteralConvertible > IntegerLiteralConvertible > StringLiteralConvertible

extension UIEdgeInsets: ArrayLiteralConvertible { public init(arrayLiteral elements: CGFloat...) { guard elements.count == 4 else { fatalError("4 CGFloats required!") } top = elements[0] left = elements[1] bottom = elements[2] right = elements[3] } } let insets: UIEdgeInsets = [10, 20, 10, 20] Swift Evolution: Tuple Convertible

HIGHER-LEVEL TYPES AS ENUMERATION RAW VALUES

"Raw values can be strings, characters, or any of the integer or floating-point number types. Each raw value must be unique within its enumeration declaration."

extension CGSize: StringLiteralConvertible { // Inspired by @terhechte public init(stringLiteral value: String) { let size = CGSizeFromString(value) self.init(width: size.width, height: size.height) } public init(extendedGraphemeClusterLiteral value: String) { let size = CGSizeFromString(value) self.init(width: size.width, height: size.height) } public init(unicodeScalarLiteral value: String) { let size = CGSizeFromString(value) self.init(width: size.width, height: size.height) } }

enum DevicesClass: CGSize { case iPhone4 = "{320, 480}" case iPhone5 = "{320, 568}" case iPhone6 = "{375, 667}" case iPhone6Plus = "{414, 736}" } let jasdevPhone = DevicesClass.iPhone6.rawValue // `CGSize`

APPLY MUTATING FUNCTIONS TO IMMUTABLE VALUES

// Credit to @jckarter func apply(transform: inout T -> U -> Void) -> T -> U -> T { return { a in { b in var c = a transform(&c)(b) return c } } } let first = [1, 2, 3] let second = [4, 5, 6] let third = apply(Array.appendContentsOf)(first)(second)

EXPERIMENTAL OPERATORS !

infix operator ∘ { associativity left precedence 100 } public func ∘(g: U -> V, f: T -> U) -> (T -> V) { return { g(f($0)) } } infix operator ∖ { associativity left precedence 140 } infix operator ∖= { associativity right precedence 90 assignment } infix operator ∪ { associativity left precedence 140 } infix operator ∪= { associativity right precedence 90 assignment } infix operator ∩ { associativity left precedence 150 } infix operator ∩= { associativity right precedence 90 assignment } infix operator ⨁ { associativity left precedence 140 } infix operator ⨁= { associativity right precedence 90 assignment } infix operator ∈ { associativity left precedence 130 } infix operator ∉ { associativity left precedence 130 } infix operator ⊂ { associativity left precedence 130 } infix operator ⊄ { associativity left precedence 130 } infix operator ⊆ { associativity left precedence 130 } infix operator ⊈ { associativity left precedence 130 } infix operator ⊃ { associativity left precedence 130 } infix operator ⊅ { associativity left precedence 130 } infix operator ⊇ { associativity left precedence 130 } infix operator ⊉ { associativity left precedence 130 }

ATTRIBUTES

@nonobjc @available @noreturn @noescape @autoclosure

@NONOBJC "Apply this attribute to a method, property, subscript, or initializer declaration to suppress an implicit objc attribute."

CUSTOM SUBSCRIPTS ON NSUserDefaults

extension NSUserDefaults { subscript(key: String) -> AnyObject? { get { return objectForKey(key) } set { setObject(newValue, forKey: key) } } subscript(key: String) -> Bool { // X - Subscript getter with Objective-C selector `objectForKeyedSubscript:` conflicts with previous declaration get { return boolForKey(key) } // X - Subscript setter with Objective-C selector `setObject:forKeyedSubscript:` conflicts with previous declaration set { setBool(newValue, forKey: key) } } // etc. }

SWIFT SUPPORTS RETURN TYPE POLYMORPHISM, OBJECTIVE-C DOESN'T. @NONOBJC TO THE RESCUE! !

extension NSUserDefaults { @nonobjc subscript(key: String) -> AnyObject? { get { return objectForKey(key) } set { setObject(newValue, forKey: key) } } @nonobjc subscript(key: String) -> Bool { get { return boolForKey(key) } set { setBool(newValue, forKey: key) } } // etc. }

@available "Apply this attribute to any declaration to indicate the declaration’s lifecycle relative to certain platforms and operating system versions."

* iOS OSX watchOS tvOS iOSApplicationExtension OSXApplicationExtension watchOSApplicationExtension tvOSApplicationExtension

class SampleViewController: UIViewController { init() { super.init(nibName: nil, bundle: nil) } @available(*, unavailable) required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") } }

@noreturn @autoclosure

@noreturn public func fatalError(@autoclosure message: () -> String = default, file: StaticString = #file, line: UInt = #line) fatalError("ayy lmao")

@noescape

// Credit to @pearapps extension Optional { func iff(@noescape f: Wrapped -> Void) { switch self { case let .Some(value): f(value) default: return } } } let foo: String? = nil func bar(a: String) { print(a) } if let foo = foo { bar(foo) } foo.iff(bar)

METATYPES

"A metatype type refers to the type of any type, including class types, structure types, enumeration types, and protocol types."

protocol Reusable: class { static var reuseIdentifier: String { get } } extension UITableView { func registerReusable(cellClass: T.Type) { registerClass(cellClass, forCellReuseIdentifier: cellClass.reuseIdentifier) } func dequeueReusable(cellClass: T.Type) -> T { guard let cell = dequeueReusableCellWithIdentifier(cellClass.reuseIdentifier) as? T else { fatalError("Misconfigured cell type, \(cellClass)!") } return cell } // ... }

class CustomCell: UITableViewCell, Reusable { static let reuseIdentifier = "customCell" } class SomeTableViewController: UITableViewController { override func viewDidLoad() { super.viewDidLoad() tableView.registerReusable(CustomCell.self) } override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell { return tableView.dequeueReusable(CustomCell.self) } // ... }

Custom Pattern Matching

infix operator ~= { associativity none precedence 130 } Standard Library implementations

func ~=(pattern: T -> Bool, value: T) -> Bool { return pattern(value) } func isEven(a: T) -> Bool { return a % 2 == 0 } let x = 3 switch x { case isEven: print("even") default: print("odd") } @olebegemann's post on pattern matching

SWIFT PRANK 1 func ~=(_: T, _: U) -> Bool { return true } 1 Don't do this

fin @jasdev @PublicExtension