A Flock of Swifts
We are a group of people excited by the Swift language. We meet each Saturday morning to share and discuss Swift-related topics.
All people and all skill levels are welcome to join.
Archives
2023.06.03
2023.05.27
Primary associatedtypes, existentials and opaque types: why you should care
With a type that has primary associatedtypes we can use the existential any to erase the type at the contract level:
struct Item { }
protocol Repository {
func getItems() -> any Publisher<[Item], Never>
}
final class EmptyRepository: Repository {
func getItems() -> any Publisher<[Item], Never> {
Just([])
}
}
final class NeverRepository: Repository {
func getItems() -> any Publisher<[Item], Never> {
Empty(completeImmediately: false)
}
}
But if we try the same thing with the opaque type it doesn't work because the compiler cannot infer a single concrete type for some Publisher<Item, Never>
protocol Repository {
// This doesn't compile
func getItems() -> some Publisher<[Item], Never>
}
final class EmptyRepository: Repository {
func getItems() -> some Publisher<[Item], Never> {
Just([])
}
}The solution is to use a generic:
protocol Repository {
associatedtype GetItemPublisher: Publisher<[Item], Never>
func getItems() -> GetItemPublisher
}
final class EmptyRepository: Repository {
func getItems() -> some Publisher<[Item], Never> {
Just([])
}
}
final class NeverRepository: Repository {
func getItems() -> some Publisher<[Item], Never> {
Empty(completeImmediately: false)
}
}While either the existential or the associatedtype + opaque type work for types with primary associatedtypes like Publisher, only the associatedtype + opaque type works for types without primary associatedtypes like AsyncSequence:
protocol AsyncRepository<Element> {
associatedtype Element
associatedtype GetItemAsyncSequence: AsyncSequence where GetItemAsyncSequence.Element == Element
func getItems() -> GetItemAsyncSequence
}
struct AsyncEmptyRepository: AsyncRepository {
typealias Element = [Item]
func getItems() -> AsyncPrefixSequence<AsyncStream<[Item]>> {
AsyncStream { [] }.prefix(1)
}
}
struct AsyncNeverRepository: AsyncRepository {
typealias Element = [Item]
func getItems() -> AsyncStream<[Item]> {
AsyncStream { nil }
}
}Stagemanger on the simulator
- simctl: https://nshipster.com/simctl/
- using simclt to enable stage manager
xcrun simctl spawn booted defaults write -g SBChamoisWindowingEnabled -bool true:https://developer.apple.com/forums/thread/708567 - open the HIG in Xcode: shift + cmd + H
demo project: switching between SplitView and TabView based on iPadOS window size:
import SwiftUI
struct ViewSizeEnvironmentKey: EnvironmentKey {
static var defaultValue: CGSize = .zero
}
extension EnvironmentValues {
var viewSize: CGSize {
get { self[ViewSizeEnvironmentKey.self] }
set { self[ViewSizeEnvironmentKey.self] = newValue }
}
}
struct MeasureModifier: ViewModifier {
let alignment: Alignment
func body(content: Content) -> some View {
GeometryReader { proxy in
content
.environment(\.viewSize, proxy.size)
.frame(width: proxy.size.width, height: proxy.size.height, alignment: alignment)
}
}
}
extension View {
func measure(alignment: Alignment = .center) -> some View {
modifier(MeasureModifier(alignment: alignment))
}
}
@MainActor
final class ViewModel: ObservableObject {
@Published var selectedTab: String
@Published var selectedItem: String?
let items = ["star", "circle", "checkmark"]
init() {
selectedTab = items[0]
selectedItem = items[0]
$selectedTab.removeDuplicates().map { $0 as String? }.assign(to: &$selectedItem)
$selectedItem.removeDuplicates().compactMap { $0 }.assign(to: &$selectedTab)
}
}
enum Platform {
#if os(macOS)
static let isMac = true
#else
static let isMac = false
#endif
}
struct RootView: View {
@StateObject private var viewModel = ViewModel()
@Environment(\.viewSize) private var viewSize
@Environment(\.horizontalSizeClass) private var horizontalSizeClass
@Environment(\.verticalSizeClass) private var verticalSizeClass
var body: some View {
if viewSize.width > 750 || Platform.isMac {
NavigationSplitView {
List(viewModel.items, id: \.self, selection: $viewModel.selectedItem) { item in
Image(systemName: item)
}
.listStyle(.sidebar)
} detail: {
content(for: viewModel.selectedItem)
}
} else {
TabView(selection: $viewModel.selectedTab) {
ForEach(viewModel.items, id: \.self) { item in
content(for: item)
.tabItem { Image(systemName: item) }
.tag(item)
}
}
}
}
func content(for item: String?) -> some View {
VStack {
Label(item ?? "no selection", systemImage: item ?? "").font(.largeTitle)
Text(String(describing: horizontalSizeClass))
Text(String(describing: verticalSizeClass))
}
}
}
struct ContentView: View {
var body: some View {
RootView().measure()
}
}
2023.05.20
Followups from Rainer
- Two line buttons don't work well. Instead he needed to use a view with a tap gesture and was able to put it in nested scroll views.
- Looking at using a base class and derived class instead of a protocol with associated types. Josh warned him it might not be as good as sticking with a protocol.
- Using transform compositions to translate and rotate points.
Transitions From Ed
Rather than using transitions mentioned last week, Ed pursued another solution. We worked on it together to simplify how it ran.
Some notes:
import SwiftUI
struct BackImage: View {
let index: Int
let size: CGSize
@State var opacity = 0.0
var x: Double {
Double.random(in: 0..<1) * size.width - 60.0
}
var y: Double {
Double.random(in: 0..<1) * size.height - 60.0
}
var delay: TimeInterval {
0.001 * Double(index)
}
var body: some View {
Image(systemName: "star.fill")
.resizable()
.foregroundColor(index.isMultiple(of: 2) ? .blue : .yellow)
.frame(width: 120, height: 120)
.offset(x: x, y: y)
.opacity(opacity)
.animation(.easeIn.delay(delay).speed(0.25),
value: opacity)
.task {
opacity = 1
}
}
}
struct BackView: View {
var body: some View {
GeometryReader { proxy in
ForEach(0..<250, id: \.self) { index in
BackImage(index: index, size: proxy.size)
}
}
}
}Discussion about Tasks
- https://developer.apple.com/videos/play/wwdc2021/10254/
- https://github.com/apple/swift-evolution/blob/main/proposals/0392-custom-actor-executors.md
New Swift Project Structure
Core team is still at the top with new Steering Groups and Workgroups.
A Great Tutorial for The Composable Architecture
Uses the Xcode tutorial format and explains The Composable Architecture.
The tutorial technology is also interesting:
- https://developer.apple.com/wwdc21/10235
- https://developer.apple.com/documentation/xcode/slothcreator_building_docc_documentation_in_xcode
Macros are coming in Swift 5.9
Kawasumi build an macro expression library called PowerAssert.
Type Erasure
We taked about Type Erasure and opening existentials.
2023.05.13
Bard and Pong
Josh tested out Google's AI Bard to make the game Pong. The result kind of worked but was a little bit dicey in how it tried to render the view.
ChatGPT seems to be better at writing Swift code at the moment but be sure to use 4, otherwise you get older, less idiomatic Swift.
Representing an optional as an array
import Foundation
let a: Int? = nil
extension Optional {
var asArray: [Wrapped] {
map { [$0] } ?? []
}
}
print(a.asArray)Another alternative (TMTOWTDI):
[b].compactMap { $0 }This approach is more "compact" (haha) but can require two allocations where the first way is always a single allocation.
Identifiable
Watch out that you don't have duplicate IDs or you will confuse the pants off of SwiftUI.
Wheel of Fortune Demo
Josh created a Wheel of Fortune using SwiftUI drawing groups for performance. Rotations effect applied do the magic of creating wedges in the proper place and spinning the wheel.
final class WheelViewModel: ObservableObject {
@Published private(set) var items: [Item] = []
@Published private(set) var angle: Angle = .zero
@Published private(set) var winner = ""
private let names: [String]
private var winningIndex = 0
let arcLength: Double
init() {
let colors: [UIColor] = [#colorLiteral(red: 0.8039215803, green: 0.8039215803, blue: 0.8039215803, alpha: 1), #colorLiteral(red: 0.9058823529, green: 0.9058823529, blue: 0.9058823529, alpha: 1), #colorLiteral(red: 0.6434109211, green: 0.625438869, blue: 0.6250535846, alpha: 1),]
let url = Bundle.main.url(forResource: "list", withExtension: "csv")
let data = try! Data(contentsOf: url!)
let text = String(data: data, encoding: .utf8)!
names = text
.components(separatedBy: .newlines)
.filter { !$0.isEmpty }
.lazy
.map { $0.localizedCapitalized }
.reduce(into: Set<String>()) { $0.insert($1) }
.sorted(by: <)
let count = Double(names.count)
arcLength = (2 * .pi) / count
items = names
.enumerated()
.map { offset, name in
.init(
name: name.description,
color: Color(uiColor: colors[offset % colors.count]),
rotation: .radians(Double(offset) * arcLength - 0.5 * .pi)
)
}
}
func tap() {
winningIndex = names.indices.randomElement() ?? 0
let remainder = fmod(angle.radians, 2.0 * .pi)
let revolutions = 2 * 2.0 * .pi + angle.radians
angle = .radians(revolutions - remainder - Double(winningIndex) * arcLength)
print("Winner: \(names[winningIndex])")
}
func showWinner() {
winner = names[winningIndex]
}
struct Item: Identifiable {
var id: String { name }
var name: String
var color: Color
var rotation: Angle
}
}
struct Wedge: View {
var title: String
var color: Color
var arcLength: Angle
var bounds: CGRect
var body: some View {
ZStack(alignment: .center) {
let center = CGPoint(x: bounds.midX, y: bounds.midY)
let radius = bounds.width / 2
let halfArcLength = Angle.radians(arcLength.radians * 0.5)
Path { path in
path.move(to: center)
path.addArc(
center: center,
radius: radius,
startAngle: -halfArcLength,
endAngle: halfArcLength,
clockwise: false
)
path.closeSubpath()
}
.foregroundColor(color)
Text(title)
.offset(x: bounds.width / 3)
.position(x: bounds.midX, y: bounds.midY)
}
}
}
struct Wheel: View {
@StateObject private var viewModel: WheelViewModel = .init()
var body: some View {
ZStack {
GeometryReader { proxy in
let bounds = proxy.frame(in: .local)
ZStack(alignment: .center) {
ForEach(viewModel.items) { item in
Wedge(title: item.name, color: item.color, arcLength: .radians(viewModel.arcLength), bounds: bounds)
.rotationEffect(item.rotation)
}
}
}
.drawingGroup()
.padding()
.rotationEffect(viewModel.angle)
GeometryReader { proxy in
let bounds = proxy.frame(in: .local)
Wedge(
title: "",
color: .cyan.opacity(0.5),
arcLength: .radians(viewModel.arcLength),
bounds: bounds
)
.rotationEffect(-.radians(0.5 * .pi))
.blendMode(.sourceAtop)
}
}
.aspectRatio(1, contentMode: .fit)
.onTapGesture {
withAnimation(.easeInOut(duration: 8)) {
viewModel.tap()
}
}
}
}
PlaygroundPage.current.setLiveView(Wheel().frame(width: 800, height: 800))2023.05.06
Mojo from Chris Lattner
It is like Python++
Upcoming Conferences
Spiral Example
Josh created a epic spiral example and blew our minds with maximum irrationality. (ϕ)
Repo: TBD
2023.04.29
Frank showed how to use NSViewRepresentable to control window zooming on macOS with SwiftUI
//
// NSWindowDemoApp.swift
// NSWindowDemo
//
// Created by Frank Lefebvre on 15/04/2023.
//
import SwiftUI
import AppKit
@main
struct NSWindowDemoApp: App {
let imageWidth = 800.0
let imageHeight = 600.0
var body: some Scene {
Window("Image", id: "main") {
ContentView()
.windowSize(idealWidth: imageWidth, idealHeight: imageHeight)
}
}
}
struct WindowAccessor: NSViewRepresentable {
let callback: (NSWindow) -> Void
private class WindowDetectingView: NSView {
private let callback: (NSWindow) -> Void
init(_ callback: @escaping (NSWindow) -> Void) {
self.callback = callback
super.init(frame: .zero)
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func viewDidMoveToWindow() {
if let window {
DispatchQueue.main.async {
self.callback(window)
}
}
}
}
func makeNSView(context: Context) -> some NSView {
WindowDetectingView(callback)
}
func updateNSView(_ nsView: NSViewType, context: Context) {
}
}
extension View {
func windowSize(idealWidth: CGFloat, idealHeight: CGFloat) -> some View {
modifier(WindowSizeModifier(idealWidth: idealWidth, idealHeight: idealHeight))
}
}
struct WindowSizeModifier: ViewModifier {
let idealWidth: CGFloat
let idealHeight: CGFloat
@State private var zoomDelegate: WindowZoomDelegate?
func body(content: Content) -> some View {
content
.background(WindowAccessor(callback: { window in
if window.styleMask.contains(.fullSizeContentView) {
let savedFrame = window.frame
window.styleMask.remove(.fullSizeContentView)
window.setFrame(savedFrame, display: false)
}
update(window: window, idealWidth: idealWidth, idealHeight: idealHeight)
zoomDelegate = WindowZoomDelegate(idealWidth: idealWidth, idealHeight: idealHeight, window: window)
window.delegate = zoomDelegate
}))
}
private func update(window: NSWindow, idealWidth: CGFloat, idealHeight: CGFloat) {
window.contentAspectRatio = .init(width: idealWidth, height: idealHeight)
}
}
final class WindowZoomDelegate: NSObject, NSWindowDelegate {
let idealWidth: CGFloat
let idealHeight: CGFloat
private weak var window: NSWindow?
private weak var target: NSWindowDelegate?
init(idealWidth: CGFloat, idealHeight: CGFloat, window: NSWindow) {
self.idealWidth = idealWidth
self.idealHeight = idealHeight
self.window = window
self.target = window.delegate
super.init()
}
func windowWillUseStandardFrame(_ window: NSWindow, defaultFrame newFrame: NSRect) -> NSRect {
guard let screenFrame = window.screen?.visibleFrame, let contentFrame = window.contentView?.frame else { return newFrame }
let proposedContentRect = window.contentRect(forFrameRect: newFrame)
let newWidth = min(idealWidth, proposedContentRect.width)
let newHeight = min(idealHeight, proposedContentRect.height)
var newOrigin = window.frame.origin
let offset = contentFrame.height - newHeight
newOrigin.y += offset
newOrigin.y = max(newOrigin.y, screenFrame.minY)
return window.frameRect(forContentRect: NSRect(x: newOrigin.x, y: newOrigin.y, width: newWidth, height: newHeight))
}
override func responds(to aSelector: Selector!) -> Bool {
Self.instancesRespond(to: aSelector) || (target?.responds(to: aSelector) ?? false)
}
override func forwardingTarget(for aSelector: Selector!) -> Any? {
target
}
}
}Josh showed a similar playground using UIViewRepresentable and the UIResponder chain to walk up the chain and mutate a UIKit type from within SwiftUI:
import UIKit
import SwiftUI
import PlaygroundSupport
struct ProxyView: UIViewRepresentable {
var onMoveToWindow: (UIView) -> Void
func makeUIView(context: Context) -> Proxy { .init() }
func updateUIView(_ proxy: Proxy, context: Context) {
proxy.onMoveToWindow = onMoveToWindow
}
final class Proxy: UIView {
var onMoveToWindow: ((UIView) -> Void)?
override func didMoveToWindow() {
super.didMoveToWindow()
guard window != nil else { return }
backgroundColor = .clear
onMoveToWindow?(self)
}
}
}
extension View {
func modifyNavigationBar(perform: @escaping (UINavigationBar) -> Void) -> some View {
background(ProxyView {
sequence(first: $0) { $0.next }
.lazy
.compactMap { $0 as? UINavigationController }
.first { _ in true }
.map(\.navigationBar)
.map(perform)
})
}
}
struct V: View {
@ViewBuilder
var body: some View {
NavigationStack {
NavigationLink("Push me") {
Text("Color changed")
.navigationTitle("I have a red bar")
.modifyNavigationBar { bar in
bar.titleTextAttributes = [.foregroundColor : UIColor.white]
bar.backgroundColor = .red
}
}
.navigationTitle("I have a blue bar")
.modifyNavigationBar { bar in
bar.prefersLargeTitles = false
bar.titleTextAttributes = [.foregroundColor : UIColor.systemYellow]
bar.backgroundColor = .blue
}
}
.navigationViewStyle(.stack)
}
}
PlaygroundPage.current.setLiveView(V())2023.04.22
Switching Between Different Xcodes
John had some questions about Xcode versions. Alex said he used this app to help with the command line
xcode-select -s stuff. It is called https://www.xcodes.app
Architecture
Some questions about architecture. There is some overhead to this solution but it puts you in a position to swap out the database implementation later.
Git Ignore
- Xcode puts stuff in .git/info/exlude
- John B. says https://github.com/github/gitignore/blob/main/Swift.gitignore
Converting Objective-C code to Swift
Josh mentions:
Wrapping PNG
Carlyn came up with a way to wrap LibPNG and all of its setjump/longjump error handling.
https://github.com/carlynorama/SwiftLIBPNG/blob/main/META.md
The source will run (eventually) on Linux. She demo'ed it this week.
TimeKeep: Testing with @Dependency
Last week we created a project timer. This week we wrote tests for it.
See https://github.com/rayfix/TimeKeep/tree/main/TimeKeep
import Dependencies
import XCTest
@testable import TimeKeep
final class TimeKeepTests: XCTestCase, @unchecked Sendable {
var dateValue: Date = .now
func testProjectTimer() {
var generator = DateGenerator { self.dateValue }
let timer = withDependencies {
$0.date = generator
} operation: {
return ProjectTimer()
}
XCTAssertFalse(timer.isRunning)
timer.start()
XCTAssert(timer.isRunning)
timer.stop()
XCTAssertFalse(timer.isRunning)
dateValue += 1
XCTAssertEqual(timer.elapsed, .zero)
timer.start()
dateValue += 1
XCTAssertEqual(timer.elapsed, .seconds(1))
dateValue += 3
XCTAssertEqual(timer.elapsed, .seconds(4))
// A stopped timer should not record elapsed time.
timer.stop()
dateValue += 400
XCTAssertEqual(timer.elapsed, .seconds(4))
}
}Golden Ratio
Josh started with his project. He showed how you can overload operators in Swift to make beautiful syntax for defining golden ratio constants 1 ± √5
2023.04.15
Recording iOS Demo Video
- Assistive touch (but it leave some extra chrome that gets recorded)
- Use "defaults write com.apple.iphonesimulator ShowSingleTouches 1" (josh)
- https://support.screenpal.com/portal/en/kb/articles/show-finger-taps-when-recording-your-screen-on-ios (via Franklin)
- https://youtu.be/DAXxgBo-Mr4 (via Franklin)
Evolution
Josh took us through some recent proposals.
is caseapple/swift-evolution#2007- Observability https://github.com/apple/swift-evolution/blob/main/proposals/0395-observability.md
TimeKeep
We created a ProjectTimer and introduced the dependency for .now
https://github.com/rayfix/TimeKeep/tree/main/TimeKeep
Mixing SwiftUI and UIKit (Part II)
import Combine
import SwiftUI
import UIKit
import PlaygroundSupport
final class VM: ObservableObject {
@Published var value = 0.0
}
final class VC: UIViewController {
@ObservedObject var viewModel = VM()
private var subscription: AnyCancellable?
init() {
super.init(nibName: nil, bundle: nil)
let label = UILabel()
let vm = viewModel
let button = UIButton(primaryAction: .init(image: .init(systemName: "arrow.counterclockwise"), handler: { _ n vm.value = 0.0 }))
let slider = ViewBinding(\.value, on: vm) { $value in
Slider(value: $value).frame(idealWidth: 300)
}
let stack = UIStackView(arrangedSubviews: [
label,
button,
UIHostingController(rootView: slider).view
])
stack.translatesAutoresizingMaskIntoConstraints = false
stack.axis = .vertical
view?.addSubview(stack)
NSLayoutConstraint.activate([
view.centerXAnchor.constraint(equalTo: stack.centerXAnchor),
view.centerYAnchor.constraint(equalTo: stack.centerYAnchor)
])
subscription = viewModel.$value
.map(String.init(describing:)).map { $0 as String? }
.assign(to: \.text, on: label)
}
@available(*, unavailable)
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
PlaygroundPage.current.setLiveView(VC())
struct ViewBinding<Target: ObservableObject, Value, Content: View>: View {
private let keypath: ReferenceWritableKeyPath<Target, Value>
@ObservedObject private var target: Target
private let content: (Binding<Value>) -> Content
init(_ keypath: ReferenceWritableKeyPath<Target, Value>,
on target: Target,
@ViewBuilder content: @escaping (Binding<Value>) -> Content) {
self.keypath = keypath
_target = .init(wrappedValue: target)
self.content = content
}
var body: some View {
content($target[dynamicMember: keypath])
}
}This lets SwiftUI respond to changes from UIKit. The key difference is
let binding = Binding<Double>(get: { vm.value },
set: { vm.value = $0 })
let slider = Slider(value: binding).frame(idealWidth: 300)versus:
let slider = ViewBinding(\.value, on: vm) { $value in
Slider(value: $value).frame(idealWidth: 300)
}2023.04.08
Discussions
- Ed was lamenting the state of HealthKit documentation. In particular, using workouts is not well documented at all.
- Activity tracking might be interesting.
- Property wrapper projected values $. It can be used to create a binding or get to a publisher depending on where you put it.
- Be careful that you don't make your EnvironmentObjects too broad. Any view listening to it will need to rebuild for any change (more precisely when objectWillChange fires).
The PNG Format
Carlyn is exploring the PNG format. She highly recommends the PNG book. Even though it is a little dated, it is extremely well written, informative, and funny.
Her repos:
Modern SwiftUI with sample app TimeKeep
Ray is starting a series to talk about modern SwiftUI heavily influenced by https://pointfree.co. Together we are building a small app TimeKeep that lets you track time for multiple projects.
- Track the time for multiple projects simultaneously
- Multiplatform (iOS, macOS, etc)
- Highly testable
- Use modern architection
We started this week by building the basic domain and some helper extensions for dealing with dates.
https://github.com/rayfix/TimeKeep/tree/main/TimeKeep
In the process we used point free library Tagged and IdentifiedArrayOf to model the domain as precisely as possible.
Meeting inspired changes
- Allen: Change the name of
TimetoTimeEvent. - Ed: Use
Calendarmethod to tell if two dates are the same day. - Josh: Use static member lookup instead of an enum for the filter predicate.
Next week
We will start putting up some UI.
Mixing SwiftUI and UIKit
Josh gave a great example of how to integrate Swift with UIKit and some of the pitfalls associated with that. The example demonstrates that using a Binding from UIKit to SwiftUI works but binding from SwiftUI to UIKit does not. We will explore how to fix this next week.
import Combine
import SwiftUI
import UIKit
import PlaygroundSupport
final class VM {
@Published var value = 0.0
}
final class VC: UIViewController {
private let viewModel = VM()
private var subscription: AnyCancellable?
init() {
super.init(nibName: nil, bundle: nil)
let label = UILabel()
let vm = viewModel
let button = UIButton(primaryAction: .init(image: .init(systemName: "arrow.counterclockwise"), handler: { _ in vm.value = 0.0 }))
let stack = UIStackView(arrangedSubviews: [
label,
button,
UIHostingController(rootView:
Slider(value: Binding<Double>(get: { vm.value }, set: { vm.value = $0 })).frame(idealWidth: 300)
).view
])
stack.translatesAutoresizingMaskIntoConstraints = false
stack.axis = .vertical
view?.addSubview(stack)
NSLayoutConstraint.activate([
view.centerXAnchor.constraint(equalTo: stack.centerXAnchor),
view.centerYAnchor.constraint(equalTo: stack.centerYAnchor)
])
subscription = viewModel.$value.map(String.init(describing:))
.map { $0 as String? }.assign(to: \.text, on: label)
}
@available(*, unavailable)
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
PlaygroundPage.current.setLiveView(VC())2023.04.01
Interfacing with C
Carlyn is documenting her explorations into using C libraries from Swift.
Swift One-liners
Franklin brought to our attention that Swift can now be invoked with -e on the command line.
What's New In Swift 5.8
Josh gave us a tour of what is available in Swift 5.8.
Morphology in Foundation
Ray reminded us that you can say, Text("\^[(count) items](inflect: true)") and
items will be pluralized properly. It works for other languages too.
Flocking Simulation (Boids)
Josh started a presentation on implementing flocking using Timeline/Canvas in SwiftUI. Some background material:
- http://www.red3d.com/cwr/papers/1987/SIGGRAPH87.pdf
- http://www.red3d.com/cwr/papers/1999/gdc99steer.html
- https://cs.stanford.edu/people/eroberts/courses/soco/projects/2008-09/modeling-natural-systems/boids.html
His implementation used an unsafe to hold the Boid type to prevent reference count traffic. You can learn about that here:
Final Project: TDB
2023.03.25
Swift Ecosystem
Apple is now sponsoring the Swift Package Index.
https://www.swift.org/blog/swift-package-index-developer-spotlight/
Github Changed Host Key
Using the Camera
Jake working through some issues with purple errors and UIRepresentable.
What's Coming in Swift
A pitch about type-safe predicates:
Elide some:
Parameter Packs
TikTok Logo Effect: Metal Shaders in CoreImage
The finished project: https://github.com/joshuajhomann/MetalCIFilter
2023.03.18
Swift Packages with C
Carlyn gave us a demo on wrapping a C package with Swift Package Manager:
Also,
Debugging Updates
TikTok Logo Effect: Metal Shaders in CoreImage
Josh began creating a sample App that lets you pick an image from your library and apply a color separating effect (think TikTok logo) on the image. This week he showed the main points:
- Create a metal file
- Add special flag -fcikernel to Other Metal Compiler Flags and Other Metal Linker Flags
- Make the function extern "C" so metal can see it.
#include <metal_stdlib>
#include <CoreImage/CoreImage.h>
using namespace metal;
extern "C" {
auto channelOffset(coreimage::sampler s, float2 redOffset, float2 greenOffset, float2 blueOffset) -> float4 {
auto index = s.coord();
return float4(
s.sample(index - redOffset).r,
s.sample(index - greenOffset).g,
s.sample(index - blueOffset).b,
s.sample(index).a
);
}
}Using the - to subract the offsets is arbitrary. (It could have been + too.)
Learning Shader Graphics:
- https://github.com/markusmoenig/ShaderMania
- https://hexler.net/kodelife
- https://thebookofshaders.com/
- https://gfxcourses.stanford.edu/cs248/winter22
2023.03.11
What's new in Swift
Swift 5.8 has been released to beta:
Also Swift 5.9 is on the way
New actor proposal
Frank's code for his talk about distributed actors: https://github.com/franklefebvre/DistributedActors-FrenchKit
Question from Allen: how to we sync state between SwiftUI and Scenekit
- Answer: have a single source of truth:
final class ViewModel: ObsevableObject {
@Published var truth
...
}- share with SwiftUI with binding via the projected value of the
StateObject:
childview($viewmodel.binding)
- share with SceneKit with a publisher projected fromt he
@Publishedproperty
scene(viewmodel.$truth)
Demo: ImageIO
Josh went over the ImageIO library and using it to read files, and image meta data. The full project is below:
2023.03.04
Conferences
- Deep Dish Swift https://deepdishswift.com
- Try Swift https://www.tryswift.co/events/2023/nyc/
Escaping Closures
@escaping means they can be stored in a property and used as a callback later.
Also recommended by Carlyn:
Generative AI for Game Assets
Metal
Josh created an Apple cross-platform app to show how to get Metal going in SwiftUI and created a MetalView. (Watch does not support metal yet.)
Roughly based on:
Also see:
You can see some amazing WebGL based demos at:
Project:
2023.02.25
WeightedStackView
Josh put together a new type of stack layout that lets each view communicate what weight it wants to the layout system. He wrote the logic for placing views in a functional style and utilized lazy sequences to avoid creation of temporary copies.
See https://developer.apple.com/documentation/swift/lazysequenceprotocol
import PlaygroundSupport
import SwiftUI
struct V: View {
var body: some View {
WeightedStackLayout(axis: .vertical, spacing: 0) {
Color.red.stack(weight: 7)
Color.green.stack(weight: 5)
Text("hi").background(Color.yellow)
Color.blue.stack(weight: 3)
Color.orange.stack(weight: 2)
Color.brown.stack(weight: 4)
Color.cyan.stack(weight: 3)
}
.frame(width: 400, height: 400)
}
}
PlaygroundPage.current.setLiveView(V())
struct WeightedStackLayoutKey: LayoutValueKey {
static var defaultValue = 1.0
}
extension View {
func stack(weight: Double) -> some View {
layoutValue(key: WeightedStackLayoutKey.self, value: weight)
}
}
extension Layout.Subviews.Element {
var stackWeight: Double {
max(self[WeightedStackLayoutKey.self], 1e-6)
}
}
struct WeightedStackLayout: Layout {
var axis: Axis = .vertical
var spacing: CGFloat = 10
func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
proposal.replacingUnspecifiedDimensions(by: .zero)
}
func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
let totalSpace = CGFloat(subviews.count - 1) * spacing
let dimension = (axis == .vertical ? bounds.height : bounds.width) - totalSpace
let pointsPerWeight = dimension / subviews.lazy.map(\.stackWeight).reduce(0, +)
let weights = subviews.lazy.map(\.stackWeight).accumulated(0, +)
let points = zip(
weights.dropLast(),
weights.dropFirst()
).enumerated().lazy.map { offset, element in
let (startWeight, endWeight) = element
let spaceBefore = spacing * CGFloat(offset)
let offset = axis == .vertical ? bounds.origin.y : bounds.origin.x
return (
start: startWeight * pointsPerWeight + spaceBefore + offset,
end: endWeight * pointsPerWeight + spaceBefore + offset
)
}
zip(subviews, points).forEach { view, point in
let distance = point.end - point.start
switch axis {
case .vertical:
view.place(
at: .init(x: bounds.midX, y: point.start + distance / 2),
anchor: .center,
proposal: .init(width: bounds.width, height: distance)
)
case .horizontal:
view.place(
at: .init(x: point.start + distance / 2, y: bounds.midY),
anchor: .center,
proposal: .init(width: distance, height: bounds.height)
)
}
}
}
}
struct LazyAccumulatedSequence<Accumulated>: LazySequenceProtocol {
private let _makeIterator: () -> Iterator
init<Element>(
underlying: some Sequence<Element>,
initial: Accumulated,
accumulate: @escaping (Accumulated, Element) -> Accumulated
) {
_makeIterator = {
var iterator = underlying.makeIterator()
var nextAccumulated: Accumulated? = initial
return Iterator {
nextAccumulated.map { accumulated in
nextAccumulated = iterator.next().map { next in
accumulate(accumulated, next)
}
return accumulated
}
}
}
}
func makeIterator() -> Iterator { _makeIterator() }
struct Iterator: IteratorProtocol {
let _next: () -> Accumulated?
mutating func next() -> Accumulated? { _next() }
}
}
extension LazySequenceProtocol {
func accumulated<Accumulated>(
_ initial: Accumulated,
_ accumulate: @escaping (Accumulated, Element) -> Accumulated
) -> LazyAccumulatedSequence<Accumulated> {
LazyAccumulatedSequence(underlying: self, initial: initial, accumulate: accumulate)
}
}
extension Sequence {
func accumulated<Accumulated>(
_ initial: Accumulated,
_ accumulate: (Accumulated, Element) throws -> Accumulated
) rethrows -> [Accumulated] {
var current = initial
var accumulated = [Accumulated]()
accumulated.reserveCapacity(underestimatedCount + 1)
accumulated.append(current)
for element in self {
current = try accumulate(current, element)
accumulated.append(current)
}
return accumulated
}
}
print([1,2,3].accumulated(0, +))
Deep linking in Apps
Josh had an example:
Learning AI
General Neural Networks
Running on you own computer
Facebook's Large Language Model
- https://ai.facebook.com/blog/large-language-model-llama-meta-ai/
- https://github.com/facebookresearch/llama
ChatGPT Client for iOS
2023.02.18
Upcoming Conferences
Edit Kit Pro
From iOSDev weekly, Ed told us about https://digitalbunker.dev/editkit-pro/
URLSessionTaskDelegate
Carlyn is doing some work on the
- https://developer.apple.com/documentation/foundation/urlsessiontaskdelegate
- https://github.com/MastodonKit/MastodonKit
- https://github.com/TootSDK/TootSDK
- https://github.com/carlynorama/TrunkLine/blob/dev/Sources/TrunkLine/Mastodon/ServerSentEventListener.swift
Models
You can do a lot of work to cleanup models by declaring custom initializers. (You don't have to expose ViewModels but can construct those internally.) You can also use custom Codable to cleanup your code.
- https://developer.apple.com/documentation/foundation/archives_and_serialization/encoding_and_decoding_custom_types
- https://quicktype.io/
Tagged
Ray revisited the Identifier<Tag> type that we looked at in November. The folks over at point free have a library that makes it easy to make unique little types.
import Tagged
struct User {
var id: Tagged<Self, UUID>
}The point free guys have a whole series on modern SwiftUI development that you can check out on their blog. https://www.pointfree.co/blog
Swift Evolution Proposals
- Attached Macros (https://forums.swift.org/t/se-0389-attached-macros/63165)
- Expression Macros (https://forums.swift.org/t/se-0382-second-review-expression-macros/63064)
- Convenience Async makeStream methods (https://forums.swift.org/t/se-0388-convenience-async-throwing-stream-makestream-methods/63139)
Unicode
Swift Strings are unique in the way that they handle Unicode. Several examples from Josh about how mutation is handled with both String and bridged NSString and NSMutableString. Swift makes a defensive copy for you when assigning.
var a: String = "a"
var b: UnsafeMutablePointer<String> = .init(&a)
a = "b"
print(a,b.pointee)
var c: NSMutableString = "c"
var d: NSString = c
c = "d"
print(c,d)
@propertyWrapper
struct Reference<Value> {
final class Wrapper<Value> {
var value: Value
init(value: Value) {
self.value = value
}
}
private var wrapper: Wrapper<Value>
var wrappedValue: Value {
get { wrapper.value }
set { wrapper.value = newValue }
}
init(wrappedValue: Value) {
wrapper = .init(value: wrappedValue)
}
}
var e = Reference(wrappedValue: "e")
var f = e
e.wrappedValue = "f"
print(e.wrappedValue, f.wrappedValue)
["âa", "áb", "àc", "ad", "äe"].lazy.map { string in
string.contains("a")
}.forEach { print($0) }
["âa", "z", "áb", "àc", "ad", "äe"].sorted { lhs, rhs in
lhs.lexicographicallyPrecedes(rhs)
}.forEach { print($0) }
["âa", "áb", "àc", "ad", "äe"].lazy.map { string in
string.localizedStandardContains("a")
}.forEach { print($0) }
["âa", "z", "áb", "àc", "ad", "äe"].sorted { lhs, rhs in
lhs.localizedCaseInsensitiveCompare(rhs) == .orderedAscending
}.forEach { print($0) }2023.02.11
Virtual Buddy
A useful tool for creating clean installs. Frank will soon be making a pull request for linux VMs.
- https://github.com/insidegui/VirtualBuddy
- https://developer.apple.com/documentation/virtualization/installing_macos_on_a_virtual_machine
Smooth Data
Common methods include moving averages, exponential smoothing, kernel smoothing, and splines.
We discussed a moving average which is probably the simplest. You can do this with a queue.
Passing Data
Although not discussed on video, this was a side discussion in the chat.
Facebook Engineering
Discussion of the technology Facebook uses (C++, Obj-C++)
If you want to do hardcore Swift, Facebook might not be your first choice.
Cross Platform SwiftUI
Although they might only have a small subset of things done.
Swift on the Command Line (Scripting)
Carlyn talked about work she is doing in VS Code and Swift
Link mentioned in chat:
A side topic to this was Swift on the Server:
Frank mentioned that the biggest gotcha is differences between implementations on Linux and macOS. Several (Josh and Franklin) noting that this will eventually be solved when Foundation becomes pure Swift:
Wordle Animation!
Josh shows how animation can be brought into the wordle app with a little restructuring. Shows the difference between implicit and explicit animation.
https://github.com/joshuajhomann/Wordle
2023.02.04
Parsing RSS Feeds
RSS is simple XML, so the the old XML Parser API should work.
Frank did some work on this previously. This project might help.
Josh implemented a partial SVG reader where he didn't implement all of the callbacks but got the information that he was interested in. See: https://github.com/joshuajhomann/SVGPasteBoard/blob/master/SVGPasteBoard/ContentView.swift
Using Custom Fonts
Ed wants his custom fonts to play nicely with the OS (and respect dynamic type).
Franklin mentioned:
@ScaledMetric(relativeTo: .largeTitle) var dynamicHeader1Size: CGFloat = 24iOS Podcast GPT
Writing Apps with ChatGPT
Emil reports that ChatGPT is helping him to get going with SwiftUI. He has reproduced a major portion of his previous app in SwiftUI in a few days where the original took him months (as he was learning).
Noting that some of the code is old (because ChatGPT was trained before 2021).
The licensing of the code is ambiguous.
Space, the final Frontier
Carlyn mentioned that many of her space friends are excited about this new release:
https://www.penguinrandomhouse.com/books/651844/critical-mass-by-daniel-suarez/
The Nature of Code
Carlyn has been working through these (knows the author) in the last couple of months:
Wordle Clone!
Josh implemented all of the game logic for his wordle clone. He used a reducer that took inputs through a tap gesture recognizer and reduced the state, modifying two properties that drive the UI updates.
https://github.com/joshuajhomann/Wordle
2023.01.28
AsyncImage Fix
Jake had an update to how he was able to fix the animation problem with AsyncImage. Here is the code:
AsyncImage(url: user.profileURL,
transaction: Transaction(animation: .default)) { phase in
switch phase {
case .success(let image):
image.resizable()
.clipShape(Circle())
.aspectRatio(contentMode: .fit)
default:
ZStack {
Circle().stroke(.black)
.frame(width: 90, height: 90)
Image(systemName: "person")
.font(.title.bold())
.scaledToFill()
}
}
}.frame(width: 90, height: 90)Non-uniform shuffling
Carlyn asked about the most Swifty way to enable non-uniform probability picking.
Some suggestions from the group:
- Look around in GameKit? (Perhaps look at this: https://www.youtube.com/watch?v=gXnuMk7AVwc)
- Create an array with duplicates of the number of elements in the probablilty you want.
- Create a special collection that vends the duplicates without actually hosting them in memory.
A related topic: https://en.wikipedia.org/wiki/Rejection_sampling
Speeding up Conformance Checking
We reviewed this blog post about how you can re-order conformance records to get a 20% performance boost.
Wurdle (Wordle Clone)
Josh continued his epic presentation on a Wordle clone. Attempted to make it work pretty. Namely, GeometryReader is not greedy and anchors things to the upper-left. You can work around it by adding a ZStack that contains a greedy view like Color.clear or Rectangle().hidden() to the ZStack.
We used the Layout protocol which is a type of view that can explicitly control the layout of a view and its subviews. Josh created a AnchorInParentLayout that lets you align an arbitrary position (UnitPoint) with an arbitrary position of the subview(s). A view modifier makes it easy to use.
2023.01.21
Layout with AsyncImage
Jake was seeing a problem with AsyncImage where the transition animation would be cancelled when the async image loaded. The image would appear at the destination without loading. Josh theorized that the problem was happening because its identity was changing. However, we could not seem to fix the problem by explicitly setting id on the views.
One recommendation is to use a much more capable third party library like Nuke.
Dates
Using Core Data to sort by date. Ed says, "CalendarComponents is your friend." Trevor recommended this resource: https://nsdateformatter.com/
Inspiration for UI
- https://dribbble.com
- https://twitter.com/_kavsoft?lang=en
- Edward Tufte
Jacey noted that SnapKit is also good (easy) way to layout views.
Sendable
Sendable conformance will be one of the important areas to be aware of as come into Swift 6. You can enable strict concurrency warnings in your build settings. The default is minimal but you can use "targetted" to check your own code.
When you enabled this checking, you will see warnings where an instance is passed across a concurrency domain and is not Sendable. For example:
func findInBackground(quadTree: QuadTree,
region: CGRect) async -> Task<[CGPoint], Never> {
Task.detached {
quadTree.find(in: region) // WARNING: QuadTree is not Sendable
}
}You can mark QuadTree as Sendable to fix this warning. This will, in turn, lead to a warning that Node, the reference type, is not sendable. If you mark Node sendable you get more warnings. This is because the class contains multiple immutable stored properties that could get modified from another concurrency domain. In this case you can mark Node with @unchecked Sendable since you know that all mutation is protected by isKnownUniquelyReferenced and makes a deep copy if it is not unique. (Aka COW.)
Benchmarks
The collection-benchmark project allows you to create benchmarks where the time might be dependent on the size of the input. We created a command-line target and included the benchmark package.
We wrote the following benchmarks:
import CollectionsBenchmark
import CoreGraphics.CGBase
struct TestPoints {
let region: CGRect
let points: [CGPoint]
init(size: Int) {
region = CGRect(origin: .zero, size: CGSize(width: size, height: size))
points = zip((0..<size).shuffled(), (0..<size).shuffled())
.map { CGPoint(x: $0.0, y: $0.1) }
}
}
var benchmark = Benchmark(title: "QuadTree Benchmarks")
benchmark.registerInputGenerator(for: TestPoints.self) { size in
TestPoints(size: size)
}
benchmark.add(title: "QuadTree find",
input: TestPoints.self) { testPoints in
let tree = QuadTree(region: testPoints.region, points: testPoints.points)
return { timer in
testPoints.points.forEach { point in
let searchRegion = CGRect(origin: point, size: .zero).insetBy(dx: -1, dy: -1)
blackHole(tree.find(in: searchRegion))
}
}
}
benchmark.addSimple(title: "Array<CGPoint> filter",
input: TestPoints.self) { testPoints in
testPoints.points.forEach { point in
let searchRegion = CGRect(origin: point, size: .zero).insetBy(dx: -1, dy: -1)
blackHole(testPoints.points.filter { candidate in
searchRegion.contains(candidate)
})
}
}
benchmark.main()Then we ran the following commands arguments:
run QuadFindResult.json --cycles 1
render QuadFindResults.json QuadFindResults.png
This produced the following results:
This is a log-log chart and you can see that the growth of the array implementation is linear.
You can see the jump at 4 items which is where the QuadTree logic is kicking in. I found that on my machine, I can boost this constant to 512 to make it always perform better than array.
You can also use a special group file to automatically produce sets of benchmarks and multiple graphs.
Wurdle
Josh continued working on the Wordle game example getting through a lot of the layout issues of the words and keyboard (adding return and backspace).
import SwiftUI
extension Color {
static let darkGray = Color(#colorLiteral(red: 0.4784313725, green: 0.4823529412, blue: 0.4980392157, alpha: 1))
static let lightGray = Color(#colorLiteral(red: 0.8274509804, green: 0.8431372549, blue: 0.8549019608, alpha: 1))
static let darkGreen = Color(#colorLiteral(red: 0.4117647059, green: 0.6705882353, blue: 0.3803921569, alpha: 1))
static let darkYellow = Color(#colorLiteral(red: 0.7960784314, green: 0.7098039216, blue: 0.3137254902, alpha: 1))
}
struct Row: Hashable, Identifiable {
var id: Int
var letters: [Letter]
}
struct Letter: Hashable, Identifiable {
var id: Int
var character: Character
var status: Status
enum Status: Int, Comparable {
static func < (lhs: Letter.Status, rhs: Letter.Status) -> Bool { lhs.rawValue < rhs.rawValue }
case unguessed, wrong, wrongPosition, correct
}
}
@MainActor
final class GameViewModel: ObservableObject {
@Published private(set) var words: [Row] = []
@Published private(set) var keys: [Row] = []
init() {
words = ["SWIFT", "CODER", "PLAYA", " ", " ", " "]
.enumerated()
.map { word in
Row(
id: word.offset,
letters: word.element.enumerated().map { character in
Letter(
id: word.offset * 10 + character.offset,
character: character.element,
status: {
switch character.element {
case " ": return Letter.Status.unguessed
case "O", "A": return .correct
case "L": return .wrongPosition
default: return .wrong
}
}()
)
}
)
}
$words
.map { rows in
let keys = rows
.lazy
.flatMap(\.letters)
.reduce(into: [Character: Letter.Status]()) { accumulated, next in
accumulated[next.character] = accumulated[next.character].map { max($0, next.status) } ?? next.status
}
return ["QWERTYUIOP", "ASDFGHJKL", "ZXCVBNM"]
.enumerated()
.map { string in
Row(
id: string.offset,
letters: string.element.enumerated().map { character in
Letter(
id: string.offset * 100 + character.offset,
character: character.element,
status: keys[character.element] ?? .unguessed
)
}
)
}
}
.assign(to: &$keys)
}
}
struct ContentView: View {
@StateObject var viewModel = GameViewModel()
var body: some View {
GeometryReader { reader in
VStack(spacing: 36) {
Grid(alignment: .topLeading, horizontalSpacing: 12, verticalSpacing: 12) {
ForEach(viewModel.words) { row in
GridRow {
ForEach(row.letters) { letter in
LetterView(style: .word(letter))
}
}
}
}
.frame(maxWidth: 600)
VStack (spacing: 12) {
ForEach(viewModel.keys) { row in
HStack(spacing: 8) {
if viewModel.keys.last == row {
LetterView(style: .keyImage("return"))
keys(for: row)
LetterView(style: .keyImage("delete.backward"))
} else {
keys(for: row)
}
}
}
}
}
.padding()
}
}
private func keys(for row: Row) -> some View {
ForEach(row.letters) { letter in
LetterView(style: .key(letter))
}
}
}
struct LetterView: View {
var style: Style
enum Style {
case key(Letter), word(Letter), keyImage(String)
}
private let fontSize: CGFloat
private let aspectRatio: CGFloat
private let textColor: Color
private let backgroundColor: Color
private let outlineColor: Color
init(style: Style) {
self.style = style
switch style {
case .keyImage:
aspectRatio = 0.66 * 1.5
fontSize = 48
textColor = .black
backgroundColor = .lightGray
outlineColor = .clear
case let .key(letter):
aspectRatio = 0.66
fontSize = 48
(textColor, backgroundColor, outlineColor) = colors(for: letter, isKey: true)
case let .word(letter):
aspectRatio = 1
fontSize = 100
(textColor, backgroundColor, outlineColor) = colors(for: letter, isKey: false)
}
func colors(for letter: Letter, isKey: Bool) -> (Color, Color, Color) {
switch (letter.status, isKey) {
case (.unguessed, true): return (.black, .lightGray, .clear)
case (.unguessed, false): return (.black, .white, .black)
case (.correct, _): return (.white, .darkGreen, .clear)
case (.wrongPosition, _): return (.white, .darkYellow, .clear)
case (.wrong, _): return (.white, .darkGray, .clear)
}
}
}
var body: some View {
GeometryReader { proxy in
RoundedRectangle(cornerRadius: 8)
.strokeBorder(outlineColor, lineWidth: 4)
.background(RoundedRectangle(cornerRadius: 8).fill(backgroundColor))
.overlay {
switch style {
case let .keyImage(name):
Image(systemName: name)
case let .key(letter), let .word(letter):
Text(String(describing: letter.character))
}
}
.foregroundColor(textColor)
.font(.system(size: fontSize, weight: .bold))
}
.aspectRatio(aspectRatio, contentMode: .fit)
}
}
2023.01.14
PointFree Dependency Injection
A new library for dependency injection was announced this week by the folks at pointfree.co. Josh gave us a quick tour of the library and an additions library:
https://github.com/pointfreeco/swift-dependencies
Peter posted this example of using the additions library:
https://twitter.com/tgrapperon/status/1612698675356250114
Ed Launches Testflight
Ed launched a private testfligt build for his new app. During the coarse of the meeting was able to find and fix an out of bounds crasher when there is no data. The power of testing in action.
Learning Swift
Some of the tried and true:
Async Result
You can create an async init for result types to get clean monadic chaining instead of nested do {} catch {} blocks. Daniel and Josh showed us how!
CoreData
Core Data is a deep subject. A good place to start:
Noise Generation
GameKit although old and written in ObjectiveC, has API for creating "natural" noise often used for procedural terrain generation in games.
Wurdle
As part of another epic, multipart demo, Josh is implementing a version of the popular game in SwiftUI. Today he created the basic model for Rows and Letters and Keys as well as the Status for each.
2023.01.07
Using contraMap Example
You can write a contramap function on CurrentValueSubject<Int> to make functions
that can send other types into the current value.
import Foundation
import Combine
extension CurrentValueSubject {
func contraMap<Value>(transform: @escaping (Value) -> Output) -> (Value) -> Void {
{ [weak self] input in
self?.send(transform(input))
}
}
}
let subject = CurrentValueSubject<Int, Never>(0)
let sendBool = subject.contraMap { (bool: Bool) in bool ? 1 : 0 }
sendBool(true)
print(subject.value)Learning SwiftUI
Core Data Debugging
Suggestions for Dan's app that has a crashing problem:
- Log non-fatal errors
- Think about all of the validations done by the Core Data model
- It reliably crashes on start
- Take note of the OS / devices it is happening on in the crash logs
- Debugging concurrency issues with -com.apple.CoreData.ConcurrencyDebug 1
Returning Swift Conferences
- https://deepdishswift.com
- https://www.swiftconf.to
- https://tryswift.jp (meetup style on 1/21)
Swift Charts Performance
Ed wrote his own charts with GeometryReader instead of SwiftUI Charts because of
performance problems on rotation and scrolling.
Photo Picker iOS16
- Jake reports it is awesome.
- Requires user iteraction so no permission is required.
- https://developer.apple.com/documentation/photokit/photospicker
New Swift Proposals
https://www.swift.org/swift-evolution/
- SE-0383 Deprecate @UIApplicationMain and @NSApplicationMain
- SE-0384 Importing Forward Declared Objective-C Interfaces and Protocols
- SE-0382 Expression Macros
Compression
The new multicore APFS aware Apple Archive framework: https://developer.apple.com/documentation/applearchive
Swift Collections
Josh took us on a guided tour of the Swift Collections package.
Exploration of CHAMP:
Aside: A Benchmarking Tool
JSON with decode indirect enum
You can represent JSON with swift with this:
enum JSON {
indirect case array([JSON])
indirect case dictionary([String: JSON])
case boolean(Bool)
case number(Double)
case string(String)
case null
}You can implement Decodable using a single value container. Naively it is a bunch of nested do {} catch {} blocks but it can be done quite succinctly by using a Result type and flatMapError to implement successive retries.
enum JSON {
indirect case array([JSON])
indirect case dictionary([String: JSON])
case boolean(Bool)
case number(Double)
case string(String)
case null
}
extension JSON: Decodable {
init(from decoder: Decoder) throws {
self = try Result { try decoder.singleValueContainer() }
.flatMap { container in
container.decodeNil()
? .success(JSON.null)
: Result { JSON.boolean(try container.decode(Bool.self)) }
.flatMapError { _ in Result { JSON.number(try container.decode(Double.self)) } }
.flatMapError { _ in Result { JSON.string(try container.decode(String.self)) } }
.flatMapError { _ in Result { JSON.array(try container.decode([JSON].self)) } }
.flatMapError { _ in Result { JSON.dictionary(try container.decode([String: JSON].self)) } }
}.get()
}
}