Concepts of programming languages Swift Lukas, Anvar, Roald, Bart, - - PowerPoint PPT Presentation

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Concepts of programming languages Swift Lukas, Anvar, Roald, Bart, - - PowerPoint PPT Presentation

Feb 22, 2023 453 likes •1.11k views

Concepts of programming languages Swift Lukas, Anvar, Roald, Bart, Lars [Faculty of Science Information and Computing Sciences] 1 Birth of a new language Swift isnt it beautiful? Developed in secret [Faculty of Science Information

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Concepts of programming languages

Swift

Lukas, Anvar, Roald, Bart, Lars

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Birth of a new language

Swift… isn’t it beautiful?

◮ Developed in secret

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Birth of a new language

Swift… isn’t it beautiful?

◮ Developed in secret ◮ Successor of Objective-C

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Objective C

◮ Introduced by NeXT

Figure 1: Steve Jobs

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Objective C

◮ Introduced by NeXT

Figure 2: Steve Jobs

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Objective C

◮ Introduced by NeXT ◮ Widely used after fjrst iPhone

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Objective C

◮ Introduced by NeXT ◮ Widely used after fjrst iPhone ◮ Steep learning curve

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Objective C

Objective-C: NSString *myString = @"Goodmorning"; NSString *test = [myString stringByAppendingString:@" Wouter"]; Python: myString = "Goodmorning"; test = myString + " Wouter";

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Swift

Apple came to the rescue and developed Swift!

◮ Inferred typing

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Swift - Inferred typing

Normal: var Str : String = "hallo" var Dbl : Double = 3.14 Inferred: var Str = "hallo" //string var Dbl = 3.14 //double

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Swift - Inferred typing

Though Swift allows inferred typing it is still static typed

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Swift

Apple came to the rescue and developed Swift!

◮ Inferred typing ◮ Neat Closures

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Swift - Closures

Without closures: func sorting(_ s1: String, _ s2: String) -> Bool { return s1 < s2 } var reversedNames = names.sorted(by: sorting) With closures: var reversedNames = names.sorted { return s1 < s2 }

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Swift

Apple came to the rescue and developed Swift!

◮ Inferred typing ◮ Neat Closures ◮ Protocols

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Swift - Pass by value or reference

Protocols are passed by value. In Swift everything except for Classes is passed by value

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Swift

Apple came to the rescue and developed Swift!

◮ Inferred typing ◮ Neat Closures ◮ Protocols ◮ Generics

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Swift

Get length of generic type func <T: count>length(_ variable: T) -> Int { return variable.count }

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Swift

Comparison with OO languages

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Parameterless function

◮ Functions are the fjrst-class citizens in both C# and Swift; // Parameterless With Return Value - C# string sayHello() { return "Hello!"; } // Parameterless With Return Value - Swift func sayHello() -> String { return "Hello!" }

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Function with Parameters

// C# string sayHello(string name) { // do something } // Swift func sayHello(name: String) -> String { // do something }

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Multiple Return Values

// C# - using a Struct struct Person { public string firstName; public string lastName; } Person getPerson() { return new Person { firstName = "Bill", lastName = "Gates" }; }

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Multiple Return Values

// Swift func getPerson() -> (firstName: String, lastName: String) { return ("Steve", "Jobs") }

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Function Parameter Name Alias

// External Parameter Names // C# // no equivalent exists // Swift func combineName(firstName first: String, lastName last: String) { // accessing the parameters can be done by referencing // "first" and "last" respectively return first + " " + last; }

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Function Types

// C# int add (int a, int b) { return a + b; } Func<int, int, int> doMath = add; var total = doMath(19, 23);

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Function Types

// Swift func add(a: Int, b: Int) -> Int { return a + b } var doMath: (Int, Int) -> Int = add var total = doMath(19, 23)

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Nested Functions

// C# int doSomething(int a, int b) { var add = new Func<int, int, int>( (first, second) => { return first + second; } ); return add(a,b); }

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Nested Functions

// Swift func doSomething(a: Int, b: Int) -> Int { func add(first: Int, second: Int) -> Int { return first + second } return add(a, b) }

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Swift

Optionals

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Optionals

What are Optionals? * Contains a value of some type or nil * Similar to Maybe in Haskell

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Optionals

How do we use Optionals? let shortForm: Int? = Int("42") let longForm: Optional<Int> = Int("42")

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Optionals

So why are they awesome?

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Optional Binding

if let myLifesPurpose: String = Optional.none { print("its something: \(myLifesPurpose)") } else { print("guess ill die") }

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Optional Chaining

class SteamId { var id = "xXx_360n0Sc0P3_xXx"} class MacUser { var steamacc:SteamId?} let wouterSwierstra = MacUser() let id = wouterSwierstra.steamacc?.id print(id) // prints nil let id2 = wouterSwierstra.steamacc?.id ?? "Y U HAVE NO STEAM?" print(id2) // prints Y U HAVE NO STEAM?

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Laziness

◮ Not standard in Swift ◮ keyword lazy ◮ more cumbersome to do than in Haskell

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Laziness

class Probe { init() { print("YOU MUST CONSTRUCT ADDITIONAL PYLONS.") } } class Protoss { lazy var builder = Probe() } var Tassadar = Protoss() //will not print "YOU MUST CONSTRUCT ADDITIONAL PYLONS."

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Laziness: infjnite list

class List{ let cur: Int init(){ cur = 3} lazy var next: List = List() func sum(cnt: Int) -> Int{ if(cnt == 0){return 0} return self.cur + self.sum(cnt: (cnt-1))} } let Buzz = List() print(Buzz.sum(cnt:140))

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Swift

Garbage Collection

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Garbage Collection

Overview

◮ Memory deallocation ◮ Only objects that are passed by reference.

Mark and Sweep

◮ Pauses program ◮ Iterates over memory at least twice ◮ Runtime delay

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Garbage Collection

Reference Counting

◮ Stores amount of references to each memory chunk ◮ Memory deallocated when counter reaches 0

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Reference Counting

Example

class Person { let name: String ... } var john = Person(name : "John Appleseed")

Figure 3: Example of a reference to memory

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Reference Counting

Pros

◮ Garbage is immediately noticed ◮ Operates at runtime ◮ Guarantees memory deallocation

Cons

◮ Reference cycles ◮ Counters in memory (space overhead) ◮ Constant counting (speed overhead) ◮ Multi-node communication

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Reference Cycle

class Person { let name: String var apartement = Apartement? ... } class Apartement { let unit: String var tenant : Person? } var john = Person(name : "John Appleseed") var unit4A = Apartement(unit : "4A") john.apartement = unit4A unit4A.tenant = john

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Reference Counting

Reference Cycle

Figure 4: Example of a reference cycle

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Reference Counting

Preventing Cycles

◮ Additional info ◮ Strong, weak, unowned reference ◮ Link without a hold

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Reference Counting

Weak Reference

◮ Does not prevent deallocation ◮ Set to nil ◮ Models optional properties ◮ For shorter target lifetime

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Reference Counting

Weak Reference

class Apartement { weak var tenant : Person? ... }

Figure 5: Example of a weak reference

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Reference Counting

Unowned Reference

◮ Does not prevent deallocation ◮ Not set to nil! ◮ For larger target lifetime ◮ Models non-optional reference ◮ Must be used safe

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Reference Counting

Unowned Reference

class Creditcard { unowned let customer : Customer ... }

Figure 6: Example of an unowned reference

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Swift

Protocols

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Protocols

A small example protocol FullyNamed { var fullName: String { get } } struct Person: FullyNamed { var fullName: String } let kees = Person(fullName: "Kees Jansen")

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Protocols

Objects in 2D plane: ◮ Squares ◮ Circle ◮ Etc. We want to know the following: ◮ Posistion ◮ Area ◮ Function: Distance to point In Swift we can use protocols for this!

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Protocols

Objects in 2D plane: ◮ Squares ◮ Circle ◮ Etc. We want to know the following: ◮ Posistion ◮ Area ◮ Function: Distance to point In Swift we can use protocols for this!

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Protocols

Defjnition

A protocol is a blueprint for functions and properties. A protocol can be adapted by a: ◮ class ◮ structure ◮ enumeration A type can conform to a protocol. Similar to interfaces in C# or type classes in Haskell.

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Protocols

Example protocol

protocol Shape { var posistion: Point { get set } var area: Double { get } func distance(point: Point) -> Double static func random() -> Self init(originpoint: Point) }

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Protocols

Protocol adapted by class

class CircleR5: Shape { var radi = 5.0 var posistion init(originpoint: Point){ self.posistion = originpoint } var area : Double { return Double.pi * radi * radi ...

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Protocols

Protocol adapted by class

class CircleR5: Shape { ... func distance(point: Point) -> Double{ //Implementation of distance function } static func random() -> CircleR5 { //Implementation of random function } }

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Protocols

Protocols as a type

Protocols can be used as a full type. For example, we have a random number generator protocol: protocol RandomNumberGenerator { func random() -> Double } And now we can defjne a function that rolls a dice: func rollD6(rng: RandomNumberGenerator) -> Int{ return Int(rng.random() * 6) + 1 }

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Protocols

Other functionallities

◮ Extend existing types to a protocol extension CircleR5 : FullyNamed{ var fullName: String { return "Circle with radius \(radi)" } }

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Protocols

Other functionallities

◮ Inheritance protocol InheritingProt: SomeProt, AnotherProt { // protocol definition goes here }

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Protocols

Other functionallities

◮ Class only protocol ClassOnlyProt: AnyObject, SomeInheritedProt { // class-only protocol definition goes here }

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Protocols

Other functionallities

◮ Composisition protocol Named { var name: String { get } } protocol Aged { var age: Int { get } } func HappyBirthday(to celebrator: Named & Aged) { print("Happy birthday, \(celebrator.name), you're \(celebrator.age)!") }

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Protocols

Other functionallities

◮ Check for protocol conformence let objects: [AnyObject] = [ CircleR5(originpoint: (2.0,0,0)), Person(name: "John"), Animal(legs: 4) ] for object in objects { if let objectWithShape = object as? Shape { print("Found a shape!") } else { print("This isn't a shape") } }

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Protocols

Other functionallities

◮ Extending protocols and default implementations extension RandomNumberGenerator { func randomBool() -> Bool { return random() > 0.5 } }

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Protocols

Comparison with Haskell Type Classes

◮ No conditional conformance (yet) (Proposal: SE-0143) extension Array: Equatable where Element: Equatable { static func ==(lhs: Array<Element>, rhs: Array<Element>) -> Bool { ... } } ◮ Haskell is not objective oriented ◮ No deriving data Maybe a = Nothing | Just a deriving (Eq, Ord)