What‘s new in Swift

import Collections

var colors: Deque = ["red", "yellow", "blue"]

colors.prepend("green")
colors.append("orange")
// `colors` is now ["green", "red", "yellow", "blue", “orange"]

colors.popFirst() // "green"
colors.popLast() // "orange"
// `colors` is back to ["red", "yellow", "blue"]

import Collections

var buildingMaterials: OrderedSet = ["straw", "sticks", "bricks"]

for i in 0 ..< buildingMaterials.count {
    print("Little piggie #\(i) built a house of \(buildingMaterials[i])")
}
// Little piggie #0 built a house of straw
// Little piggie #1 built a house of sticks
// Little piggie #2 built a house of bricks

buildingMaterials.append("straw") // (inserted: false, index: 0)

import Collections

var responses: OrderedDictionary = [200: "OK", 403: "Forbidden", 404: "Not Found"]

for (code, phrase) in responses {
    print("\(code) (\(phrase))")
}
// 200 (OK)
// 403 (Forbidden)
// 404 (Not Found)

import Algorithms

let testAccounts = [ ... ]

for testGroup in testAccounts.uniquePermutations(ofCount: 0...) {
    try validate(testGroup)
}

let randomGroup = testAccounts.randomSample(count: 5)

import System

let fd: FileDescriptor = try .open(
    "/tmp/a.txt", .writeOnly,
    options: [.create, .truncate], permissions: .ownerReadWrite)
try fd.closeAfter {
    try fd.writeAll("Hello, WWDC!\n".utf8)
}

import System

var path: FilePath = "/tmp/WWDC2021.txt"
print(path.lastComponent)         // "WWDC2021.txt"

print(path.extension)             // "txt"
path.extension = "pdf"            // path == "/tmp/WWDC2021.pdf"
path.extension = nil              // path == "/tmp/WWDC2021"
print(path.extension)             // nil

path.push("../foo/bar/./")        // path == "/tmp/wwdc2021/../foo/bar/."
path.lexicallyNormalize()         // path == "/tmp/foo/bar"
print(path.ends(with: "foo/bar")) // true!

import Numerics

let x: Float16 = 1.5
let y = Float16.exp(x)

import Numerics

let z = Complex(0, Float16.pi) // πi
let w = Complex.exp(z)         // exp(πi) ≅ -1

import AWSLambdaRuntime
import AWSLambdaEvents

@main
struct HelloWorld: LambdaHandler {
    typealias In = APIGatewayV2Request
    typealias Out = APIGatewayV2Response
    func handle(event: In, context: Lambda.Context) async throws -> Out {
        .init(statusCode: .ok, body: "Hello World")
    }
}

class Traveler {
    var destination: String
}

func test() {
    let traveler1 = Traveler(destination: "Unknown")
    // retain
    let traveler2 = traveler1
    // release
    traveler2.destination = "Big Sur"
    // release
    print("Done traveling")
}

enum Command {
    case load(key: String)
    case store(key: String, value: Int)
}

// You used to have to manually implement all of this boilerplate.

enum Command: Codable {
    case load(key: String)
    case store(key: String, value: Int)

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        if container.allKeys.count != 1 {
            let context = DecodingError.Context(
                codingPath: container.codingPath,
                debugDescription: "Invalid number of keys found, expected one.")
            throw DecodingError.typeMismatch(Command.self, context)
        }

        switch container.allKeys.first.unsafelyUnwrapped {
        case .load:
            let nested = try container.nestedContainer(
                keyedBy: LoadCodingKeys.self,
                forKey: .load)
            self = .load(
                key: try nested.decode(String.self, forKey: .key))
        case .store:
            let nested = try container.nestedContainer(
                keyedBy: StoreCodingKeys.self,
                forKey: .store)
            self = .store(
                key: try nested.decode(String.self, forKey: .key),
                value: try nested.decode(Int.self, forKey: .value))
        }
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        switch self {
        case let .load(key):
            var nested = container.nestedContainer(keyedBy: LoadCodingKeys.self, 
                                                   forKey: .load)
            try nested.encode(key, forKey: .key)
        case let .store(key, value):
            var nested = container.nestedContainer(keyedBy: StoreCodingKeys.self, 
                                                   forKey: .store)
            try nested.encode(key, forKey: .key)
            try nested.encode(value, forKey: .value)
        }
    }

    /// Contains keys for all cases of the enum.
    enum CodingKeys: CodingKey {
        case load
        case store
    }

    /// Contains keys for all associated values of `case load`.
    enum LoadCodingKeys: CodingKey {
        case key
    }

    /// Contains keys for all associated values of `case store`.
    enum StoreCodingKeys: CodingKey {
        case key
        case value
    }
}

enum Command: Codable {
    case load(key: String)
    case store(key: String, value: Int)
}

enum Coffee {
    case regular
    case decaf
}

func brew(_ coffee: Coffee) { ... }

brew(.regular)

protocol Coffee { ... }
struct RegularCoffee: Coffee { }
struct Cappuccino: Coffee { }
extension Coffee where Self == Cappucino {
    static var cappucino: Cappucino { Cappucino() }
}

func brew<CoffeeType: Coffee>(_ coffee: CoffeeType) { ... }

brew(.cappucino.large)

@propertyWrapper
struct NonEmpty<Value: Collection> {
    init(wrappedValue: Value) {
        precondition(!wrappedValue.isEmpty)
        self.wrappedValue = wrappedValue
    }

    var wrappedValue: Value {
        willSet { precondition(!newValue.isEmpty) }
    }
}

func logIn(@NonEmpty _ username: String) {
    print("Logging in: \(username)")
}

// Instead of writing this...

import SwiftUI

struct SettingsView: View {
    @State var settings: [Setting]

    private let padding = 10.0

    var body: some View {
        List(0 ..< settings.count) { index in
            #if os(macOS)
            Toggle(settings[index].displayName, isOn: $settings[index].isOn)
                .toggleStyle(CheckboxToggleStyle())
            #else
            Toggle(settings[index].displayName, isOn: $settings[index].isOn)
                .toggleStyle(SwitchToggleStyle())
            #endif
        }
        .padding(CGFloat(padding))
    }
}

// You can now write this.

import SwiftUI

struct SettingsView: View {
    @State var settings: [Setting]

    private let padding = 10.0

    var body: some View {
        List($settings) { $setting in
            Toggle(setting.displayName, isOn: $setting.isOn)
              #if os(macOS)
              .toggleStyle(.checkbox)
              #else
              .toggleStyle(.switch)
              #endif
        }
        .padding(padding)
    }
}

// Instead of writing this...

func fetchImage(id: String, completion: (UIImage?, Error?) -> Void) {
    let request = self.imageURLRequest(for: id)
    let task = URLSession.shared.dataTask(with: request) {
        data, urlResponse, error in
        if let error = error {
            completion(nil, error)
        } else if let httpResponse = urlResponse as? HTTPURLResponse,
                httpResponse.statusCode != 200 {
            completion(nil, MyTransferError())
        } else if let data = data, let image = UIImage(data: data) {
            completion(image, nil)
        } else {
            completion(nil, MyOtherError())
        }
    }
   task.resume()
}

let (data, response) = try await URLSession.shared.data(for: request)

// You can now write this.

func fetchImage(id: String) async throws -> UIImage {
    let request = self.imageURLRequest(for: id)
    let (data, response) = try await URLSession.shared.data(for: request)
    if let httpResponse = response as? HTTPURLResponse,
       httpResponse.statusCode != 200 {
        throw TransferFailure()
    }
    guard let image = UIImage(data: data) else {
        throw ImageDecodingFailure()
    }
    return image
}

func titleImage() async throws -> Image {
    async let background = renderBackground()
    async let foreground = renderForeground()
    let title = try renderTitle()
    return try await merge(background,
                           foreground,
                           title)
}

actor Statistics {
    private var counter: Int = 0
    func increment() {
        counter += 1
    }
    func publish() async {
        await sendResults(counter)
    }
}

var statistics = Statistics()
await statistics.increment()