| language | contributors | filename | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
swift |
|
learnswift.swift |
Swift is a programming language for iOS and OS X development created by Apple. Designed to coexist with Objective-C and to be more resilient against erroneous code, Swift was introduced in 2014 at Apple's developer conference WWDC. It is built with the LLVM compiler included in Xcode 6+.
The official Swift Programming Language book from Apple is now available via iBooks.
See also Apple's getting started guide, which has a complete tutorial on Swift.
// import a module
import UIKit
//
// MARK: Basics
//
// Xcode supports landmarks to annotate your code and lists them in the jump bar
// MARK: Section mark
// TODO: Do something soon
// FIXME: Fix this code
// In Swift 2, println and print were combined into one print method. Print automatically appends a new line.
print("Hello, world") // println is now print
print("Hello, world", appendNewLine: false) // printing without appending a newline
// variables (var) value can change after being set
// constants (let) value can NOT be changed after being set
var myVariable = 42
let øπΩ = "value" // unicode variable names
let π = 3.1415926
let convenience = "keyword" // contextual variable name
let weak = "keyword"; let override = "another keyword" // statements can be separated by a semi-colon
let `class` = "keyword" // backticks allow keywords to be used as variable names
let explicitDouble: Double = 70
let intValue = 0007 // 7
let largeIntValue = 77_000 // 77000
let label = "some text " + String(myVariable) // Casting
let piText = "Pi = \(π), Pi 2 = \(π * 2)" // String interpolation
// Build Specific values
// uses -D build configuration
#if false
print("Not printed")
let buildValue = 3
#else
let buildValue = 7
#endif
print("Build value: \(buildValue)") // Build value: 7
/*
Optionals are a Swift language feature that either contains a value,
or contains nil (no value) to indicate that a value is missing.
A question mark (?) after the type marks the value as optional.
Because Swift requires every property to have a value, even nil must be
explicitly stored as an Optional value.
Optional<T> is an enum.
*/
var someOptionalString: String? = "optional" // Can be nil
// same as above, but ? is a postfix operator (syntax candy)
var someOptionalString2: Optional<String> = "optional"
if someOptionalString != nil {
// I am not nil
if someOptionalString!.hasPrefix("opt") {
print("has the prefix")
}
let empty = someOptionalString?.isEmpty
}
someOptionalString = nil
/*
Trying to use ! to access a non-existent optional value triggers a runtime
error. Always make sure that an optional contains a non-nil value before
using ! to force-unwrap its value.
*/
// implicitly unwrapped optional
var unwrappedString: String! = "Value is expected."
// same as above, but ! is a postfix operator (more syntax candy)
var unwrappedString2: ImplicitlyUnwrappedOptional<String> = "Value is expected."
if let someOptionalStringConstant = someOptionalString {
// has `Some` value, non-nil
if !someOptionalStringConstant.hasPrefix("ok") {
// does not have the prefix
}
}
// Swift has support for storing a value of any type.
// AnyObject == id
// Unlike Objective-C `id`, AnyObject works with any value (Class, Int, struct, etc.)
var anyObjectVar: AnyObject = 7
anyObjectVar = "Changed value to a string, not good practice, but possible."
/*
Comment here
/*
Nested comments are also supported
*/
*/
//
// MARK: Collections
//
/*
Array and Dictionary types are structs. So `let` and `var` also indicate
that they are mutable (var) or immutable (let) when declaring these types.
*/
// Array
var shoppingList = ["catfish", "water", "lemons"]
shoppingList[1] = "bottle of water"
let emptyArray = [String]() // let == immutable
let emptyArray2 = Array<String>() // same as above
var emptyMutableArray = [String]() // var == mutable
// Dictionary
var occupations = [
"Malcolm": "Captain",
"kaylee": "Mechanic"
]
occupations["Jayne"] = "Public Relations"
let emptyDictionary = [String: Float]() // let == immutable
let emptyDictionary2 = Dictionary<String, Float>() // same as above
var emptyMutableDictionary = [String: Float]() // var == mutable
//
// MARK: Control Flow
//
// for loop (array)
let myArray = [1, 1, 2, 3, 5]
for value in myArray {
if value == 1 {
print("One!")
} else {
print("Not one!")
}
}
// for loop (dictionary)
var dict = ["one": 1, "two": 2]
for (key, value) in dict {
print("\(key): \(value)")
}
// for loop (range)
for i in -1...shoppingList.count {
print(i)
}
shoppingList[1...2] = ["steak", "peacons"]
// use ..< to exclude the last number
// while loop
var i = 1
while i < 1000 {
i *= 2
}
// do-while loop
do {
print("hello")
} while 1 == 2
// Switch
// Very powerful, think `if` statements with syntax candy
// They support String, object instances, and primitives (Int, Double, etc)
let vegetable = "red pepper"
switch vegetable {
case "celery":
let vegetableComment = "Add some raisins and make ants on a log."
case "cucumber", "watercress":
let vegetableComment = "That would make a good tea sandwich."
case let localScopeValue where localScopeValue.hasSuffix("pepper"):
let vegetableComment = "Is it a spicy \(localScopeValue)?"
default: // required (in order to cover all possible input)
let vegetableComment = "Everything tastes good in soup."
}
//
// MARK: Functions
//
// Functions are a first-class type, meaning they can be nested
// in functions and can be passed around
// Function with Swift header docs (format as reStructedText)
/**
A greet operation
- A bullet in docs
- Another bullet in the docs
:param: name A name
:param: day A day
:returns: A string containing the name and day value.
*/
func greet(name: String, day: String) -> String {
return "Hello \(name), today is \(day)."
}
greet("Bob", "Tuesday")
// similar to above except for the function parameter behaviors
func greet2(#requiredName: String, externalParamName localParamName: String) -> String {
return "Hello \(requiredName), the day is \(localParamName)"
}
greet2(requiredName:"John", externalParamName: "Sunday")
// Function that returns multiple items in a tuple
func getGasPrices() -> (Double, Double, Double) {
return (3.59, 3.69, 3.79)
}
let pricesTuple = getGasPrices()
let price = pricesTuple.2 // 3.79
// Ignore Tuple (or other) values by using _ (underscore)
let (_, price1, _) = pricesTuple // price1 == 3.69
print(price1 == pricesTuple.1) // true
print("Gas price: \(price)")
// Variadic Args
func setup(numbers: Int...) {
// its an array
let number = numbers[0]
let argCount = numbers.count
}
// Passing and returning functions
func makeIncrementer() -> (Int -> Int) {
func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)
// pass by ref
func swapTwoInts(inout a: Int, inout b: Int) {
let tempA = a
a = b
b = tempA
}
var someIntA = 7
var someIntB = 3
swapTwoInts(&someIntA, &someIntB)
print(someIntB) // 7
//
// MARK: Closures
//
var numbers = [1, 2, 6]
// Functions are special case closures ({})
// Closure example.
// `->` separates the arguments and return type
// `in` separates the closure header from the closure body
numbers.map({
(number: Int) -> Int in
let result = 3 * number
return result
})
// When the type is known, like above, we can do this
numbers = numbers.map({ number in 3 * number })
// Or even this
//numbers = numbers.map({ $0 * 3 })
print(numbers) // [3, 6, 18]
// Trailing closure
numbers = sorted(numbers) { $0 > $1 }
print(numbers) // [18, 6, 3]
// Super shorthand, since the < operator infers the types
numbers = sorted(numbers, < )
print(numbers) // [3, 6, 18]
//
// MARK: Structures
//
// Structures and classes have very similar capabilities
struct NamesTable {
let names = [String]()
// Custom subscript
subscript(index: Int) -> String {
return names[index]
}
}
// Structures have an auto-generated (implicit) designated initializer
let namesTable = NamesTable(names: ["Me", "Them"])
let name = namesTable[1]
print("Name is \(name)") // Name is Them
//
// MARK: Classes
//
// Classes, structures and its members have three levels of access control
// They are: internal (default), public, private
public class Shape {
public func getArea() -> Int {
return 0;
}
}
// All methods and properties of a class are public.
// If you just need to store data in a
// structured object, you should use a `struct`
internal class Rect: Shape {
var sideLength: Int = 1
// Custom getter and setter property
private var perimeter: Int {
get {
return 4 * sideLength
}
set {
// `newValue` is an implicit variable available to setters
sideLength = newValue / 4
}
}
// Lazily load a property
// subShape remains nil (uninitialized) until getter called
lazy var subShape = Rect(sideLength: 4)
// If you don't need a custom getter and setter,
// but still want to run code before and after getting or setting
// a property, you can use `willSet` and `didSet`
var identifier: String = "defaultID" {
// the `willSet` arg will be the variable name for the new value
willSet(someIdentifier) {
print(someIdentifier)
}
}
init(sideLength: Int) {
self.sideLength = sideLength
// always super.init last when init custom properties
super.init()
}
func shrink() {
if sideLength > 0 {
--sideLength
}
}
override func getArea() -> Int {
return sideLength * sideLength
}
}
// A simple class `Square` extends `Rect`
class Square: Rect {
convenience init() {
self.init(sideLength: 5)
}
}
var mySquare = Square()
print(mySquare.getArea()) // 25
mySquare.shrink()
print(mySquare.sideLength) // 4
// cast instance
let aShape = mySquare as Shape
// compare instances, not the same as == which compares objects (equal to)
if mySquare === mySquare {
print("Yep, it's mySquare")
}
// Optional init
class Circle: Shape {
var radius: Int
override func getArea() -> Int {
return 3 * radius * radius
}
// Place a question mark postfix after `init` is an optional init
// which can return nil
init?(radius: Int) {
self.radius = radius
super.init()
if radius <= 0 {
return nil
}
}
}
var myCircle = Circle(radius: 1)
print(myCircle?.getArea()) // Optional(3)
print(myCircle!.getArea()) // 3
var myEmptyCircle = Circle(radius: -1)
print(myEmptyCircle?.getArea()) // "nil"
if let circle = myEmptyCircle {
// will not execute since myEmptyCircle is nil
print("circle is not nil")
}
//
// MARK: Enums
//
// Enums can optionally be of a specific type or on their own.
// They can contain methods like classes.
enum Suit {
case Spades, Hearts, Diamonds, Clubs
func getIcon() -> String {
switch self {
case .Spades: return "♤"
case .Hearts: return "♡"
case .Diamonds: return "♢"
case .Clubs: return "♧"
}
}
}
// Enum values allow short hand syntax, no need to type the enum type
// when the variable is explicitly declared
var suitValue: Suit = .Hearts
// Non-Integer enums require direct raw value assignments
enum BookName: String {
case John = "John"
case Luke = "Luke"
}
print("Name: \(BookName.John.rawValue)")
// Enum with associated Values
enum Furniture {
// Associate with Int
case Desk(height: Int)
// Associate with String and Int
case Chair(String, Int)
func description() -> String {
switch self {
case .Desk(let height):
return "Desk with \(height) cm"
case .Chair(let brand, let height):
return "Chair of \(brand) with \(height) cm"
}
}
}
var desk: Furniture = .Desk(height: 80)
print(desk.description()) // "Desk with 80 cm"
var chair = Furniture.Chair("Foo", 40)
print(chair.description()) // "Chair of Foo with 40 cm"
//
// MARK: Protocols
//
// `protocol`s can require that conforming types have specific
// instance properties, instance methods, type methods,
// operators, and subscripts.
protocol ShapeGenerator {
var enabled: Bool { get set }
func buildShape() -> Shape
}
// Protocols declared with @objc allow optional functions,
// which allow you to check for conformance
@objc protocol TransformShape {
optional func reshaped()
optional func canReshape() -> Bool
}
class MyShape: Rect {
var delegate: TransformShape?
func grow() {
sideLength += 2
// Place a question mark after an optional property, method, or
// subscript to gracefully ignore a nil value and return nil
// instead of throwing a runtime error ("optional chaining").
if let allow = self.delegate?.canReshape?() {
// test for delegate then for method
self.delegate?.reshaped?()
}
}
}
//
// MARK: Other
//
// `extension`s: Add extra functionality to an already existing type
// Square now "conforms" to the `Printable` protocol
extension Square: Printable {
var description: String {
return "Area: \(self.getArea()) - ID: \(self.identifier)"
}
}
print("Square: \(mySquare)")
// You can also extend built-in types
extension Int {
var customProperty: String {
return "This is \(self)"
}
func multiplyBy(num: Int) -> Int {
return num * self
}
}
print(7.customProperty) // "This is 7"
print(14.multiplyBy(3)) // 42
// Generics: Similar to Java and C#. Use the `where` keyword to specify the
// requirements of the generics.
func findIndex<T: Equatable>(array: [T], valueToFind: T) -> Int? {
for (index, value) in enumerate(array) {
if value == valueToFind {
return index
}
}
return nil
}
let foundAtIndex = findIndex([1, 2, 3, 4], 3)
print(foundAtIndex == 2) // true
// Operators:
// Custom operators can start with the characters:
// / = - + * % < > ! & | ^ . ~
// or
// Unicode math, symbol, arrow, dingbat, and line/box drawing characters.
prefix operator !!! {}
// A prefix operator that triples the side length when used
prefix func !!! (inout shape: Square) -> Square {
shape.sideLength *= 3
return shape
}
// current value
print(mySquare.sideLength) // 4
// change side length using custom !!! operator, increases size by 3
!!!mySquare
print(mySquare.sideLength) // 12
// Operators can also be generics
infix operator <-> {}
func <-><T: Equatable> (inout a: T, inout b: T) {
let c = a
a = b
b = c
}
var foo: Float = 10
var bar: Float = 20
foo <-> bar
print("foo is \(foo), bar is \(bar)") // "foo is 20.0, bar is 10.0"