Some of my favourite swift tricks
209. Password generator - Random string
randomString(length: 6) // dff32KS
func randomString(length: Int) -> String {
// Define the characters that can be used in the random string
let characters: String = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
// Generate an array of random characters from the `characters` string
let randomCharacters: [String.Element] = (0..<length).compactMap { _ in
characters.randomElement()
}
// Convert the array of characters into a string and return it
return String(randomCharacters)
}
208. if/else statements as expressions
This makes the code easier to read and write, especially when you need to assign a value to a variable based on multiple conditions.
Before, you might have used nested ternary operators, which can be hard to read:
// Assign a value to 'output' based on multiple conditions
let output = (condA ? valA :
condB ? valB :
condC ? valC :
valD)
With Swift 5.9, you can use if/else expressions instead, which are easier to understand:
// Assign a value to 'output' using if/else expressions
let output = if condA {
valA
} else if condB {
valB
} else if condC {
valC
} else {
valD
}
207. switch statements as expressions
This new feature is also useful when you need to assign a value to a global variable or a stored property based on a switch statement. Before, you would have to use a closure:
// Assign a value to 'sound' based on the type of 'creature'
let sound: String = {
switch creature {
case .dog:
return "Woof"
case .cat:
return "Meow"
case .cow:
return "Moo"
default:
return "Unknown sound"
}
}()
Now, you can use a switch expression, which is simpler and cleaner:
// Assign a value to 'sound' using a switch expression
let sound: String = switch creature {
case .dog:
"Woof"
case .cat:
"Meow"
case .cow:
"Moo"
default:
"Unknown sound"
}
206. Native with:
with is awesome, but you have to add it to every app and lib to use it. Instead here is a native way to get with like capabilities:
[page].forEach {
$0.name = "John"
$0.page = 3
$0.publishedAt = .now
}
205. Simple performance timing:
let c: CFTimeInterval = CACurrentMediaTime()
usleep(useconds_t(0.002)) // Simulates heavy task here for 2 milliseconds (.002 seconds)
let c1: CFTimeInterval = CACurrentMediaTime() - c
Swift.print("Time past: \(c1)") // 0.002
204. Dynamic lookup on disctionary:
The documentation at https://docs.swift.org/swift-book/ReferenceManual/Attributes.html says that you can use this feature to find members of a class, structure, enumeration, or protocol by their name when the program is running. To use this, the type needs to have a special function called subscript(dynamicMemberLookup:).
@dynamicMemberLookup
struct Employee {
var data = [String: String]()
subscript(dynamicMember member: String) -> String {
return data[member] ?? "Data not available"
}
}
var employee = Employee()
employee.data["name"] = "Jane"
print(employee.name) // Jane
print(employee.position) // Data not available
Even though the Contact class doesn’t have a ‘name’ or ‘email’, the program won’t give an error. This is because it checks for these members when it’s running, not before. If it can find ‘name’ or ‘email’, it uses those. If it can’t, it just uses a default value.
203. Convert OrderedDictionary to Dictionary:
import OrderedCollections // get this from apples SPM repo on github
let x: OrderedDictionary = [
"200": "OK",
"403": "Access forbidden",
"404": "File not found",
"500": "Internal server error",
]
extension OrderedDictionary where Key: Hashable, Value: Any {
var dictionary: [Key: Value] {
self.reduce(into: [Key: Value]()) { (result, element) in
result[element.key] = element.value
}
}
}
x.dictionary // outputs regular dictionary
202. Get a dictoary from a class or struct instance:
func asDictionary(target: Any) -> [String: Any] {
let mirror = Mirror(reflecting: target)
let dict: [String: Any] = Dictionary(uniqueKeysWithValues: mirror.children.lazy.map({ (label: String?, value: Any) -> (String, Any)? in
guard let label = label else { return nil }
return (label, value)
}).compactMap { $0 })
return dict
}
usage:
let p1 = Person(name: "Ryan", position: 2, good : true, car:"Ford")
print(p1.asDictionary) // outputs dictionary
201. Generic typealias:
Generic typealias can be used to simplify param types etc
typealias Parser<A> = (String) -> [(A, String)]
Usage:
func parse<A>(stringToParse: String, parser: Parser)
200. AnyComparable
In Swift 5.9, you can write a method using parameter packs. Here I implemented the sorting using the built-in KeyPathComparator:
extension Array {
mutating func sort<each T: Comparable>(by keyPaths: repeat (KeyPath<Element, each T>, SortOrder)) {
var comparators: [KeyPathComparator<Element>] = []
func addComparator<Key: Comparable>(_ keyPathOrder: (KeyPath<Element, Key>, SortOrder)) {
comparators.append(KeyPathComparator(keyPathOrder.0, order: keyPathOrder.1))
}
// here I am technically creating a tuple, with its elements all being addComparator calls
// this could be written more readably when we can iterate over a parameter pack with a for loop
(repeat addComparator(each keyPaths))
sort(using: comparators)
}
}
Example Usage:
// order by length of string ascendingly, then by the string itself descendingly
someStrings.sort(by: (\.count, .forward), (\.self, .reverse))
With that, you can write your sort method signature as:
mutating func sort(by criteria: (path: KeyPath<Element, AnyComparable>, order:OrderType)...) {
...
}
To make it easier for us to pass key paths with the type AnyComparable in, we can make an extension:
extension Comparable {
// this name might be too long, but I'm sure you can come up with a better name
var anyComparable: AnyComparable {
.init(self)
}
}
Now we can do:
someArray.sort(by: (\.key1.anyComparable, .asc), (\.key2.anyComparable, .asc))
199. Extension for Array where Element is Optional
This might be a bit complex, but it’s possible to create an AnyOptional protocol. This protocol would require an associated type (Wrapped) and a computed property to return the optional type. If the index is valid, the element is returned unwrapped; if not, nil is returned.
protocol AnyOptional {
associatedtype Wrapped
var optional: Optional<Wrapped> { get }
}
extension Optional: AnyOptional {
var optional: Optional<Wrapped> { self }
}
extension Collection {
subscript(safe index: Index) -> Element? {
indices.contains(index) ? self[index] : nil
}
}
extension Collection {
subscript(safe index: Index) -> Element.Wrapped? where Element: AnyOptional {
indices.contains(index) ? self[index].optional ?? nil : nil
}
}
var myArray: [String?] = ["2", "banana", nil, "31"]
var myStringArray: [String] = ["2", "3"]
let item = myArray[safe: 1] // item is String?
let strItem = myStringArray[safe: 99] // strItem is String?
198. How to use optional binding in swit
This involves “rebinding” (⚠️️ There might be a weay to make this generic ⚠️️)
import SwiftUI
extension Binding where Value == Date? {
func flatten(defaultValue: Date) -> Binding<Date> {
Binding<Date>( // We "rebin"d" here
get: { wrappedValue ?? defaultValue },
set: { wrappedValue = $0 }
)
}
}
DatePicker(
"",
selection: $date.flatten(defaultValue: Date()), // Use the optional value, if it's nil use the default
displayedComponents: .hourAndMinute
)
.datePickerStyle(WheelDatePickerStyle())
197. Singleton variable for SwiftUI view
SwiftUI views cant be singletons. But we can tie a global variable to a view. This example shows how we can control showing a sheet from anywhere. If the view is available.
var prefrencesSheetHandler = PrefsSheetHandler() // must be in global scope
/**
* - Note: Solution found here: https://stackoverflow.com/questions/70870750/swiftui-modify-state-var-from-remote-closure
* ## Examples:
* prefsSheetHandler.isShowingSheet = true // <-- add anywhere
* $prefsSheetHandler.isShowingSheet // add to sheet isPresneting variable
* @ObservedObject var prefsSheetHandler: PrefsSheetHandler = prefrencesSheetHandler // add in the view scope
*/
class PrefsSheetHandler: ObservableObject {
@Published var isShowingSheet = false
}
196. Multi cursor in xCode:
- Draw multiple lines: alt + drag
- Select multiple cursor positions: ctrl + cmd
195. Check if a string is an email
// "kenmueller0@gmail.com".isValidEmail // true
extension String {
var isValidEmail: Bool {
NSPredicate(format: "SELF MATCHES %@", "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}").evaluate(with: self)
}
}
194. Finding Elements of Specific Type in Swift
extension Array {
func whereType<T> () -> [T] {
compactMap { $0 as? T } // The function "compactMap(" in Swift is incredibly useful. It maps each element of an array to another optional type and returns the value if it exists (is not null).
}
}
func testIt() {
let array = [1, 2, "3", 4.0, 5] as [Any]
let ints: [Int] = array.whereType? // You now have the ability to filter elements in an array based on their specific types.
print(ints) // prints [1, 2, 5]
}
193. Sum of Any Numeric Types in Swift
In Swift, all numeric values, including “Int”, “Float”, “Double”, and “CGFloat”, conform to the “Numeric” protocol. By applying a generic constraint to your array extension, you can make methods available for all numeric types in your array.
extension Array where Element: Numeric){
sum () -> Self. Element {
reduce (0, +) //By employing the "reduce" function and the "+" operator, you can efficiently compute the sum of all elements in the array. Isn't that neat?
}
}
// Observe how the "sum" function's return value matches the type of the array's elements!
func testit( {
let sumOfDoubles = [1.1, 4,4, 8.8]. sum ()
print (sum0fDoubles) // 14.3
let sumOfInts = [1, 4, 8]. sum() *
print(sumOfInts) // 13.0
let sumOfFloats: Float = [1.1, 4,4, 8.81. sum ()
print (sumOfFloats) // 14.3
}
192. Async getters in Swift 5.5+
struct LazyImageFromFile {
enum Errors: Error {
case invalidFilePath
}
let filePathOnDisk: URL
init(filePathOnDisk: URL) throws { // In the constructor of our struct, we accept a file URL. If the URL does not point to a valid file, an error will be thrown.
guard filePathOnDisk.isFileURL else {
throw Errors.invalidFilePath
self.filePathOnDisk = filePathOnDisk
}
}
var data: Data {
get async throws { // Introduced in Swift 5.5, you can now establish a getter as an asynchronous getter. This implies that the receiver will need to use "await", similar to JavaScript or Flutter, to obtain its underlying value.
try Data( contents0f: self. filePathOnDisk,
options: .mappedIfSafe)
}
}
func testIt () async throws { // In the function where we are testing our structure, we designate it as an asynchronous function. This allows us to use the "await" keyword when calling our data's asynchronous getter.
guard let fileUrl = Bundle.main.url( forResource: "myimage"
withExtension: "jpg") else {
return
}
let lazyImage = try LazyImageFromFile(filePathOnDisk: fileUrl)
let contents = try await lazyImage.data // Finally, we will access the getter from our struct using the "try await" syntax, as the getter is marked as asynchronous and can potentially throw an error.
print (contents)
}
191. Actors in Swift 5.5+:
actor Stack<T> { // The keyword "actor" introduced in Swift 5.5+ facilitates the creation of isolates. These isolates, managed by the actor, ensure thread-safety at a fundamental level within the actor by maintaining it's isolated data types.
private var _items = [T] ()
init items: [T] = [1) {
self._items = items
@discardableResult
func push (_ value: T) async -> T {
await _items.append(value) // Despite the "append(" function of Array in Swift not being an asynchronous function, by prefixing it with 'await' within this asynchronous function, we indicate that we are establishing a lock on our "_items" private variable.
return value
}
func pop () async -> T {
let popped = await _items.removeLast() // Likewise, when we are deleting an item from the end of our stack, we use 'await' on the result. Even though 'removeLast(' is not an asynchronous function, this approach establishes a lock on '_items' until 'removeLast' has completed its operation.
return popped
}
var items: [T] {
get async { //Additionally, we provide a read-only access to our items using an asynchronous getter, a feature introduced in Swift 5.5+.
_items
}
}
}
func testIt() async {
let stack1 = Stack<Int> ( [1, 2, 31)
let stack2 = Stack<Int> ( [4, 5, 6])
await stack2.push (await stack1.push(10))
await stack2.push(await stack1.pop())
let stack1Count = await stack1.items. count
let stack2Count = await stack2.items. count
assert (stack1Count == 3)
assert (stack2Count == 5)
}
190. Lazy Local Variables in Swift 5.5+
Beginning with Swift 5.5, it’s possible to declare lazy local variables that are only evaluated upon their first use, similar to how lazy variables function at the class or struct level.
func incremented (_ value: Int) -> Int {
value + 1
}
func testIt() {
var value = 1
lazy var inc = incremented (value)
value += 1
print (inc) // 3
}
// Here, we initialize 'value' to 1. The 'incremented' function, which takes 'value' as an argument, won't be invoked until 'value +=1' is executed. This is because 'value' is first used in the print statement.
189. Accessing Plist directly
if let path = NSBundle.mainBundle().pathForResource("Config", ofType: "plist") {
if let dict = NSDictionary(contentsOfFile: path) as? Dictionary<String, AnyObject> {
// use swift dictionary as normal
}
}
188. Different ways to create random numbers
See also: https://nemecek.be/blog/89/randomness-in-swift-comprehensive-overview
let randomBool = Bool.random()
let randomInt = Int.random(in: 1...6) // dice roll
let randomFloat = Float.random(in: 0...1)
let randomDouble = Double.random(in: 1..<100)
187. Useful string modifiers and parsers:
// Beginning of a string
let index = str.index(str.startIndex, offsetBy: 5)
let mySubstring = str[..<index] // Hello
// Prefix:
let index = str.index(str.startIndex, offsetBy: 5)
let mySubstring = str.prefix(upTo: index) // Hello
let mySubstring = str.prefix(5) // Hello
// End of a string subscripts:
let index = str.index(str.endIndex, offsetBy: -10)
let mySubstring = str[index...] // playground
// Suffix:
let index = str.index(str.endIndex, offsetBy: -10)
let mySubstring = str.suffix(from: index) // playground
let mySubstring = str.suffix(10) // playground
//Range in a string
let start: String.Index = str.index(str.startIndex, offsetBy: 7)
let end: String.Index = str.index(str.endIndex, offsetBy: -6)
let range: Range<String.Index> = start..<end
let mySubstring = str[range] // play
186. Avoiding boilerplate code “required init”
open class BaseView: UIView {
/**
* Initiate
*/
override public init(frame: CGRect = .zero) {
super.init(frame: frame)
}
/**
* Boilerplate
*/
@available(*, unavailable) // This line avoids the requirement in subsequent subclasses etc
public required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
185. Selected or all selected
extension UITextInput {
var selectedOrFullTextRange: UITextRange {
return selectedTextRange // Return the selected text range if it exists
?? textRange( // If the selected text range does not exist, try to get the text range from the beginning of the document to the end of the document
from: self.beginningOfDocument,
to: self.endOfDocument)
?? UITextRange() // If the text range cannot be obtained, return an empty `UITextRange`
}
}
184. Current scene
extension UIApplication {
var cur rentScene: UIWindowScene? {
connectedScenes // Get all the connected scenes
.first { $0.activationState == .foregroundActive } // Find the first scene whose activation state is `.foregroundActive`
as? UIWindowScene // Cast the scene to `UIWindowScene`
}
}
183. Openable URL
"https://google.com".isOpenableURL // true
extension String {
var isOpenableURL: Bool {
guard let url = URL(string: self) else { return false } // Try to create a URL object from the string, return false if it fails
guard url.scheme != nil else { return false } // Check if the URL has a scheme, return false if it does not have a scheme
guard UIApplication.shared.canOpenURL(url) else { return false } // Check if the URL can be opened by the shared application, return false if it cannot be opened
return true // Return true if the URL can be opened
}
}
182. Weak wrapper:
let weakArr = [“a”, “b”, 2].wrapped weakArr // Weak(“a”), Weak(“b”), Weak(2) weakArr.unWrapped // a,b,2
public class Weak<T: AnyObject> {
public weak var value: T?
public init(_ value: T) {
self.value = value
}
}
typealias WeakArray = [Weak]
extension WeakArray where T == AnyObject{
var wrapped: [Weak<T>] {
map { Weak($0) }
}
var unWrapped: [T] {
compactMap { $0.value }
}
}
181. Clamped range:
public extension Comparable {
func clamped(to limits: ClosedRange<Self>) -> Self {
return min(max(self, limits.lowerBound), limits.upperBound)
}
}
print(25.clamped(to: 0...20)) // 20
180. Create instances based on dynamic class types
let isSecure: Bool = false // or true
var baseType: NSTextField.Type {
self.isSecure ? NSSecureTextField.self : NSTextField.self
}
let tf: NSTextField = self.baseType.init(frame: .zero) // Creates secure or normal textfield
170. Find parent view control
public var parentViewController: NSViewController? {
sequence(first: self, next: \.nextResponder).compactMap({ $0 as? NSViewController }).first
}
169. Find where to insert something
extension Collection {
/**
* - Fixme: ⚠️️ add doc
* - Remark: Slower than binary search
* ## Examples:
* let arr = ["a", "g", "r"]
* let idx = arr.insertionIndex(of: "r", using: <)
* rowData.insert("m", at: idx) // ["a", "g", "m", "r"]
*/
func insertionIndex(of element: Self.Iterator.Element, using areInIncreasingOrder: (Self.Iterator.Element, Self.Iterator.Element) -> Bool) -> Index {
firstIndex { !areInIncreasingOrder($0, element) } ?? endIndex
}
}
/**
* Binary Search
*/
extension RandomAccessCollection where Element: Comparable {
func insertionIdx(of value: Element) -> Index {
var slice: SubSequence = self[...] // Initialize a variable `slice` with a subsequence of the string
while !slice.isEmpty { // Loop while the slice is not empty
let middle = slice.index(slice.startIndex, offsetBy: slice.count / 2) // Get the middle index of the slice
if value < slice[middle] { // Check if the value is less than the middle element of the slice
slice = slice[..<middle] // If the value is less than the middle element, update the slice to the left half of the slice
} else {
slice = slice[index(after: middle)...] // If the value is greater than or equal to the middle element, update the slice to the right half of the slice
}
}
return slice.startIndex // Return the start index of the slice
}
}
168: let closure
Sometimes you want to store a method in a variable
typealias Message = (_ oldPSW: String, _ newPSW: String) -> String
let message: Message = { oldPSW, newPSW in
"Change from old password: \(oldPSW) to new: \(newPSW)"
}
print(message("abc", "123")) // "Change from old password: abc to new: 123"
167: Collection over array:
- If you know you’re going to be working with other collection types, and you don’t want to incur the cost of allocating an array
- Usually, Array is a good currency type, but if you’re writing a parser or some other code where you expect to be handed an ArraySlice or something like that, you could do it the way you posted.
- This also allows for things like display(users:) to work with data types like Set, for example.
- In general it just allows display(users:) to be much more flexible. I wouldn’t say that it’s something that you should always write “by default” instead of [User]/Array
, but if you find yourself creating display(users: [User]) and another version display(users: Set ) and another version display(users: ArraySlice ) (and so on), then just using some Collection makes this much more flexible and reduces a lot of code. - It can be useful for making functions more flexible, but also be careful with it, because certain assumptions are no longer valid:
- Here you just want to iterate over a collection, fine But if you want to display users, that collection should be sorted. Array is, Set isn’t. It won’t give an error at compile time, and it’ll run fine, but your UI will be inconsistent (tests might fail?)
- Certainly. Hence the “don’t just default to the style just because.” Use it with purpose.
struct User {
let firstName: String
}
func display(users: some Collection<User>) {
for user in users {
print(user)
}
}
166: shorthand if-let syntax
var userName: String?
if let userName {
// `userName` is non-optional here
}
165: large number separators
let bigNumber = 123_456_789
164. KeyPaths in closures
extension Int {
var isEven: Bool { self.isMultiple(of: 2) }
}
let numbers = [1, 2, 3, 4, 5]
let evens = numbers.filter(\.isEven)
163. Use dump call to get more info
class Person {
init(name: String, age: Int) {
self.name = name
self.age = age
}
var name: String
var age: Int
}
let me = Person(name: "Vincent", age: 31)
dump(me)
162. Where condition in array iterating:
let numbers = [1, 2, 3, 4, 5]
for number in numbers where number.isMultiple(of: 2) {
print(number)
}
161. Better actions for UIButtons
// ioS14+
var label: UILabel
var button: UIButton
var counter = 0 {
didSet {
label.text = "Counter: \(counter)"
}
}
override func viewDidLoad() {
super.viewDidLoad()
button.addAction(UIAction { [weak self] _ in
self?.counter += 1
}, for: .touchUpInside)
}
160. Using result to handle async calls:
func fetchData(_ completion: @escaping (Result<Data, Error>) -> Void) {
/* ... */
}
fetchData { result in
switch result {
case .success(let data):
// use the data
case .failure(let error):
// handle the error
}
}
159. some isntead of generic
func handle(value: some Identifiable) {
/* ... */
}
158. switch on tuples
switch (boolean1: boolean1, boolean2: boolean2, boolean3: boolean3) {
case (boolean1: true, _, boolean3: false):
functionA()
case (_, boolean2: false, boolean3: true):
functionB()
case (boolean1: true, boolean2: false, boolean3: false):
functionC()
default:
break
}
157. string or empty
extension Optional where Wrapped == String {
var orEmpty: String {
self ?? ""
}
}
let optionalString = Bool.random() ? "Hello, world!" : nil
print(optionalString.orEmpty)
156. string is nil or empty
extension Optional where Wrapped == String {
var isNilOrEmpty: Bool {
self == nil || self == ""
}
}
func handles(optionalString: String?) {
if optionalString.isNilOrEmpty == false {
// use `optionalString`
}
}
155. Json string:
let json = #"{"name":"Vincent"}"#
154. Optional extension
extension String? {
var orEmpty: String {
self ?? ""
}
}
153. Lazy let
class ViewController: UIViewController {
private(set) lazy var subview: UIView = {
let view = UIView()
// configure `view`
return view
}()
}
152. Safe way to return element at specified index
You can extend collections to return the element at the specified index if it is within bounds, otherwise nil.
extension Collection {
subscript (safe index: Index) -> Element? {
return indices.contains(index) ? self[index] : nil
}
}
let cars = ["Lexus", "Ford", "Volvo", "Toyota", "Opel"]
let selectedCar1 = cars[safe: 3] // Toyota
let selectedCar2 = cars[safe: 6] // not crash, but nil
151. Tips for writing error messages
- Say what happened and why
- Suggest a next step
- Find the right tone (If it’s a stressful or serious issue, then a silly tone would be inappropriate)
150. Split array by chunks of given size:
Great extension to split array by chunks of given size
extension Array {
func chunk(_ chunkSize: Int) -> [[Element]] {
return stride(from: 0, to: self.count, by: chunkSize).map({ (startIndex) -> [Element] in
let endIndex = (startIndex.advanced(by: chunkSize) > self.count) ? self.count-startIndex : chunkSize
return Array(self[startIndex..<startIndex.advanced(by: endIndex)])
})
}
}
149. Lightweight way to add content changing animation to UIView
Just invoke 🧙♂️ fadeTransition(_ duration: CFTimeInterval) by your view before you will apply a change.
extension UIView {
func fadeTransition(_ duration: CFTimeInterval) {
let animation = CATransition() // Create a new `CATransition` object
animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut) // Set the timing function of the animation to ease in and ease out
animation.type = kCATransitionFade // Set the type of the animation to fade
animation.duration = duration // Set the duration of the animation to the specified duration
layer.add(animation, forKey: kCATransitionFade) // Add the animation to the layer with the specified key
}
}
Example:
label.fadeTransition(1)
label.text = "Updated test content with animation"
148. Remove dups
Clear way to return the unique list of objects based on a given key. It has the advantage of not requiring the Hashable and being able to return an unique list based on any field or combination.
extension Array {
func unique<T:Hashable>(map: ((Element) -> (T))) -> [Element] {
var set: Set<T> = [] // Initialize an empty set of type `T`
var arrayOrdered: [Element] = [] // Initialize an empty array of type `Element`
for value in self { // Loop through each value in the sequence
if !set.contains(map(value)) { // Check if the set does not contain the mapped value of the current value
set.insert(map(value)) // If the set does not contain the mapped value, insert the mapped value into the set
arrayOrdered.append(value) // Append the current value to the ordered array
}
}
return arrayOrdered // Return the ordered array
}
}
147. Dispatch group
Let’s say you’ve got several long running tasks to perform. After all of them have finished, you’d like to run some further logic. You could run each task in a sequential fashion, but that isn’t so efficient - you’d really like the former tasks to run concurrently. DispatchGroup enables you to do exactly this.
let dispatchGroup = DispatchGroup()
for i in 1...5 {
dispatchGroup.enter()
Alamofire.request(url, parameters: params).responseJSON { response in
//work with response
dispatchGroup.leave()
}
}
dispatchGroup.notify(queue: .main) {
print("All requests complete")
}
In the above, all long running functions will perform concurrently, followed by the print statement, which will execute on the main thread.
Each call to enter() must be matched later on with a call to leave(), after which the group will call the closure provided to notify().
DispatchGroup has a few other tricks:
Instead of notify(), we can call wait(). This blocks the current thread until the group’s tasks have completed. A further option is wait(timeout:). This blocks the current thread, but after the timeout specified, continues anyway. To create a timeout object of type DispatchTime, the syntax .now() + 1 will create a timeout one second from now. wait(timeout:) returns an enum that can be used to determine whether the group completed, or timed out.
146. Asynchronous work in Playground.
Tell the playground it should continue running forever, otherwise it will terminate before the asynchronous work has time to hppen.
PlaygroundPage.current.needsIndefiniteExecution = true
145. Delegate naming:
your method names will should use will, did, and should
144. Protocol naming:
Protocols: Naming
If we are talking about naming the protocol itself:
Protocols that describe what something is should read as nouns (e.g. Collection). Protocols that describe a capability should be named using the suffixes able, ible, or ing (e.g. Equatable, ProgressReporting).
143. Optional protocol methos:
// If you implement a protocol in Swift you must implement all its requirements. Optional methods are not allowed.
protocol CarDelegate {
func engineDidStart()
func carShouldStartMoving() -> Bool
func carDidStartMoving()
func engineWillStop()
func engineDidStop()
}
// But there are a few tricks how to make some methods to be optionals:
// You can split them in two protocols, and adopt only needed one.
protocol CarMovingStatusDelegate {
func carShouldStartMoving() -> Bool
func carDidStartMoving()
}
protocol CarEngineStatusDelegate {
func engineDidStart()
func engineWillStop()
func engineDidStop()
}
142. Result type without value to provide
enum Result<T> {
case success(result: T)
case failure(error: Error)
}
func login(with credentials: Credentials, handler: @escaping (_ result: Result<User>) -> Void) {
// Two possible options:
handler(Result.success(result: user))
handler(Result.failure(error: UserError.notFound))
}
// login(with:) operation has user value to provide and default Result type fits perfectly here. But let’s imagine that your operation hasn’t got value to provide or you don’t care about it. Default Result type makes you to provide the result value any way.
// To fix this inconvenience you need to add extension and instantiate a generic with an associated value of type Void.
func login(with credentials: Credentials, handler: @escaping (_ result: Result<Void>) -> Void)
extension Result where T == Void {
static var success: Result {
return .success(result: ())
}
}
// Now we can change our func login(with:) a bit, to ignore result success value if we don’t care about it.
func login(with credentials: Credentials, handler: @escaping (_ result: Result<Void>) -> Void) {
// Two possible options:
handler(Result.success)
handler(Result.failure(error: UserError.notFound))
}
141. XCTUWrap
In Xcode 11 new assertion function has been added for use in Swift tests. XCTUnwrap asserts that an Optional variable’s value is not nil, returning the unwrapped value of expression for subsequent use in the test. It protects you from dealing with conditional chaining for the rest of the test. Also it removes the need to use XCTAssertNotNil(::file:line:) with either unwrapping the value. It’s common to unwrap optional before checking it for a particular value so that’s really where XCTUnwrap() will come into its own.
struct Note {
var id: Int
var title: String
var body: String
}
class NotesViewModel {
static func all() -> [Note] {
return [
Note(id: 0, title: "first_note_title", body: "first_note_body"),
Note(id: 1, title: "second_note_title", body: "second_note_body"),
]
}
}
func testGetFirstNote() throws {
let notes = NotesViewModel.all()
let firstNote = try XCTUnwrap(notes.first)
XCTAssertEqual(firstNote.title, "first_note_title")
}
140. URL components
Dictionary of the URL’s query parameters
extension URL {
var queryParameters: [String: String]? {
guard let components = URLComponents(url: self, resolvingAgainstBaseURL: false) else { return nil } // Try to create a URL components object from the URL string, return nil if it fails
guard let queryItems = components.queryItems else { return nil } // Get the query items from the URL components, return nil if there are no query items
var items: [String: String] = [:] // Initialize an empty dictionary of type `[String: String]`
for queryItem in queryItems { // Loop through each query item
items[queryItem.name] = queryItem.value // Add the query item name and value to the dictionary
}
return items // Return the dictionary of query parameters
}
}
139. Numeric sum
Sum Function for Numeric Collection
extension Collection where Element: Numeric {
func sum() -> Element {
return self.reduce(0, +)
}
}
[3, 4, 6].sum() // 13
[3.4, 6.2, 7.3].sum() // 16.9
138. Remove dups:
public extension Array where Element: Hashable {
public mutating func removeDups() {
self = unified()
}
}
public extension Collection where Element: Hashable {
public func unified() -> [Element] {
return reduce(into: []) { // Reduce the sequence to an array, initialized with an empty array
if !$0.contains($1) { // Check if the array does not contain the current element
$0.append($1) // If the array does not contain the current element, append the current element to the array
}
}
}
}
var array = [1, 2, 3, 3, 2, 1, 4]
array.removeDups() // [1, 2, 3, 4]
137. Quality of service:
Apps and operations compete to use finite resources: memory, network interfaces, CPU, and so on. In order to remain responsive and efficient, the system needs to prioritize tasks and make intelligent decisions about when to execute them.
A quality of service (QoS) class allows you to categorize work to be performed by NSOperation, NSOperationQueue, NSThread objects, dispatch queues, and pthreads (POSIX threads). By assigning a QoS to work, you indicate its importance, and the system prioritizes it and schedules it accordingly.
// Work is virtually instantaneous.
DispatchQoS.userInteractive
// Work is nearly instantaneous, such as a few seconds or less.
DispatchQoS.userInitiated
// Work takes a few seconds.
DispatchQoS.default
// Work takes a few seconds to a few minutes.
DispatchQoS.utility
// Work takes significant time, such as minutes or hours.
DispatchQoS.background
136. One to many observer pattern:
The Observer design pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. The Observer pattern is essentially a publish-and-subscribe model in which the subject and its observers are loosely coupled. Communication can take place between the observing and observed objects without either needing to know much about the other. Cocoa implements the observer pattern in two ways: Notifications and Key-Value Observing (KVO).
// Observer Pattern
protocol Observer {
var id : Int { get } // property to get an id
func update<ObservableValue>(with newValue: ObservableValue)
}
protocol Observable {
associatedtype ObservableValue // Declare an associated type `ObservableValue`
var value : ObservableValue { get set } // Declare a variable `value` of type `ObservableValue`
var observers : [Observer] { get set } // Declare a variable `observers` of type `[Observer]`
func addObserver(observer: Observer) // Declare a method `addObserver` that takes an `Observer` object as a parameter
func removeObserver(observer: Observer) // Declare a method `removeObserver` that takes an `Observer` object as a parameter
func notifyAllObservers<ObservableValue>(with newValue: ObservableValue) // Declare a generic method `notifyAllObservers` that takes a new value of type `ObservableValue` as a parameter and notifies all observers
}
135. Mutating structs with a function call
If you need to modify the properties of your structure or enumeration within a particular method, you can opt in to mutating behavior for that method.
struct Point {
var x = 0.0, y = 0.0
mutating func moveBy(x deltaX: Double, y deltaY: Double) {
x += deltaX
y += deltaY
}
}
var somePoint = Point(x: 1.0, y: 1.0)
somePoint.moveBy(x: 2.0, y: 3.0)
print("The point is now at (\(somePoint.x), \(somePoint.y))")
// Prints "The point is now at (3.0, 4.0)"
134. count where
The new count(where:) method:
let scores = [100, 80, 85]
let passCount = scores.count { $0 < 90 }
133. Class and instance name
String(describing: UIView.self) // "UIView"
String(describing: type(of: UILabel())) // "UILabel"
132. Multiline string
"""
The red fox walked down the
street. It was not jumping the fence.
"""
131. Implicit and explicit getters
struct A {
let data: Data
var cellData: Data { data } // Wrong 🚫 (because it looks like its a variable)
}
struct A {
let data: Data
var getCellData: Data { data } // Correct ✅ (clearly indicates that it is a getter)
}
130. Clamping a value:
We can also do: Swift.max(minVal, Swift.min(maxVal, val))
/**
* Clamp
* ## Examples:
* CGFloat.clamp(val: 44, min: 33, max: 38) // 38
* - Parameters:
* - val: target value
* - min: no less
* - max: no more
* - Returns: clamped value
*/
internal static func clamp(val: CGFloat, min: CGFloat, max: CGFloat) -> CGFloat {
if val <= min { // Under
return min
} else if val >= max { // Over
return max
} else { // Between
return val
}
}
129. Data conversion
Data extension for conversion
extension Data {
// Unarchive data into an object and return as type `Any`.
public func convert() -> Any? {
return NSKeyedUnarchiver.unarchiveObject(with: self)
}
// Converts an object into Data using NSKeyedArchiver
public static func toData(object: Any) -> Data {
return NSKeyedArchiver.archivedData(withRootObject: object)
}
}
128. Using packages to test things quick
Problem:
- Playground is nice but hit and miss sometimes
- Online swift compilers are iffy, and debug log is gnarly
- Swift code in the terminal is awesome, but terminal isnt grat for typing code
Solution:
- Create a ScratchPad swift package
- Drag it into xcode
- Use unit-test to run xode
127. Change string with a range:
let input = "Hello, world"
let range = NSMakeRange(4, 8)
// To make that into a Swift Range instance you just need this single line of code:
let swiftRange = Range(range, in: input)
print(swiftRange.lowerBounds) // 0
print(swiftRange.upperBounds) // 10
input.replaceSubstring(range, "****")
print(input) // he****ld
126. Comparing two arrays where the item has a custom equality method
struct Item {
let id: String
let date: Int
}
extension Item {
func isEqual(other: Item) -> Bool {
return self.id == other.id
}
}
typealias Items = [Item]
extension Array where Element == Item {
func isEqual(others: Items) -> Bool {
let intersection = self.filter { item in others.contains { $0.isEqual(other: item) } }
return intersection.count == others.count && intersection.count == self.count // its important to assert count on both arrays
}
}
let x: Items = [
.init(id: "a", date: 0),
.init(id: "b", date: 1),
.init(id: "c", date: 2)
]
let y: Items = [
.init(id: "a", date: 0),
.init(id: "b", date: 1),
.init(id: "c", date: 2)
]
let z: Items = [
.init(id: "a", date: 7),
.init(id: "d", date: 5),
.init(id: "f", date: 2)
]
print(x.isEqual(others: y)) // true
print(x.isEqual(others: z)) // false
print(y.isEqual(others: z)) // false
125. Overriding super type method
Subclassing works even tho the Util method only knows about the base type
class A {
func merge(item: A) {
insert()
}
func insert() {
Swift.print("A.insert")
}
}
class B: A {
override func insert() {
Swift.print("B.insert")
super.insert()
}
}
class Util {
static func merge(item: A) {
item.merge(item: item)
}
}
let item: A = B()
Util.merge(item: item)
// prints B.insert then A.insert
124. Assert that an array intersects another
let a = [3, 4]
let b = [2, 1, 3]
let intersection = a.filter { item in b.contains { $0 == item } }
print(intersection.count == a.count) // false -> its missing 4
123. Find the first VC in a VC hierarchy
Put this in a UIVC Extension. Usage: let topAlertController: UIAlertController? = topMostVC?.firstMatch()
/**
* Traverses the entire VC hierarchy downwards and returns the first match
* - Parameter type: Class type to match
*/
public func firstMatch<T: UIViewController>(type: T.Type? = nil) -> T? {
self.children.first {
$0.firstMatch(type: type) != nil
} as? T
}
122. Add a comment to infoplist
Because infoplist is complicated, and there is a lot of knowledge attached to choices of which key/val that are stored in infoplist
<!-- A Boolean value indicating whether the app may open the original document from a file provider, rather than a copy of the document. -->
121. Random range:
Int.random(in: 8...44) // random int between 8 and 44
(8..<44).randomElement() ?? 8 // random int between 8 and 44
String(Int.random(in: (1000..<9999))) // 4 digit code like 4413, 9999 etc
120. Struct vs Class
- If it’s basically a bag of data, use a struct
- If it has a lifecycle, use a class
119. Switch on tuples:
Great for testing groups of cases
let state = (a: true, b: false, c: "123")
switch state {
case (true, _, _): print("a is true")
case (_, _, "123"): print("c has 123 text")
case (_, _, _): print("Did not find a match")
}
118: Golden path:
When coding with conditionals, the left-hand margin of the code should be the “golden” or “happy” path. That is, don’t nest if statements. Multiple return statements are OK. The guard statement is built for this.
func computeFFT(context: Context?, inputData: InputData?) throws -> Frequencies {
guard let context = context else {
throw FFTError.noContext
}
guard let inputData = inputData else {
throw FFTError.noInputData
}
// Use context and input to compute the frequencies
return frequencies
}
117: Shorthand syntax for unwrapping optionals
For Swift 5.7 and up
if let textContainer {
// do many things with textContainer
}
116: for-where Loops
When the entirety of a for loop’s body would be a single if block testing a condition of the element, the test is placed in the where clause of the for statement instead.
// instead of:
for item in collection {
if item.hasProperty {
// ...
}
}
// do this:
for item in collection where item.hasProperty {
// ...
}
// for-where Loops
// When the entirety of a for loop’s body would be a single if block testing a condition of the element, the test is placed in the where clause of the for statement instead
for item in collection where item.hasProperty {
// ...
}
for item in collection {
if item.hasProperty {
// ...
}
}
115: String from enum case:
Also works even if a case is assigned a string
enum CarType {
case ford, volvo, fiat
}
String(describing: CarType.ford) // ford
114: Autoclousure:
func printTest1(_ result: () -> Void) {
print("Before")
result()
print("After")
}
printTest1({ print("Hello") })
// With auto-closure:
func printTest2(_ result: @autoclosure () -> Void) {
print("Before")
result()
print("After")
}
printTest2(print("Hello"))
113: Using where in guards
- Using where is the same as using comma, but can be more human readable.
- Also a reminder to use where in other places. like for-loops. Which is easy to forget etc
currentRequest?.getValue { [weak self] result in guard let user = result.okValue where result.errorValue == nil else { // Check if the `okValue` of the result is not nil and the `errorValue` of the result is nil self?.showRequestError(result.errorValue) // If the `okValue` is nil or the `errorValue` is not nil, show the request error self?.isPerformingSignUp = false // Set the `isPerformingSignUp` flag to false return // Return from the method } self?.finishSignUp(user) // If the `okValue` is not nil and the `errorValue` is nil, finish the sign up process with the user object }
112. Add property wrapper to user default
@propertyWrapper
struct UserDefault<T: Codable> {
let key: String // Declare a constant `key` of type `String`
let defaultValue: T // Declare a constant `defaultValue` of type `T`
init(_ key: String, defaultValue: T) {
self.key = key // Set the `key` property to the specified key
self.defaultValue = defaultValue // Set the `defaultValue` property to the specified default value
}
var wrappedValue: T {
get {
if let data = UserDefaults.standard.object(forKey: key) as? Data, // Try to get the data from the user defaults for the specified key
let user = try? JSONDecoder().decode(T.self, from: data) { // Try to decode the data as an object of type `T`
return user // If the decoding succeeds, return the decoded object
}
return defaultValue // If the decoding fails or the data does not exist, return the default value
} set {
if let encoded = try? JSONEncoder().encode(newValue) { // Try to encode the new value as JSON data
UserDefaults.standard.set(encoded, forKey: key) // Set the encoded data in the user defaults for the specified key
}
}
}
}
enum GlobalSettings {
@UserDefault("user", defaultValue: User(name:"",pass:"")) static var user: User
}
// Example User model confirm Codable
struct User:Codable {
let name:String
let pass:String
}
// How to use it
// Set value
GlobalSettings.user = User(name: "Ahmed", pass: "Ahmed")
// GetValue
print(GlobalSettings.user) // Ahmed
111. Use defer in init instad of didSet
Invoke didSet when property’s value is set inside init context. Apple’s docs specify that: “Property observers are only called when the property’s value is set outside of initialization context.” Defer can change situation:
class AA {
var propertyAA: String! {
didSet {
print("Function: \(#function)")
}
}
init(propertyAA: String) {
self.propertyAA = propertyAA
}
}
class BB {
var propertyBB: String! {
didSet {
print("Function: \(#function)")
}
}
init(propertyBB: String) {
defer {
self.propertyBB = propertyBB
}
}
}
let aa = AA(propertyAA: "aa")
let bb = BB(propertyBB: "bb")
110. Curried calls that throw
- This is an effort to reduce methods in an API.
- Here we attach the network call in a closure block.
- Usually we would duplicate the database api calls for network.
- Like:
insertAndSync,deleteAndSync,deleteAllAndSyncand 10 more etc - Instead we attach the network call in a parameter to the database API
- Bonus: We can read the error from the POV of the caller if network produce one etc
- Bonus: The database API stays the same. If we don’t add the complete param, everything is unchanged ```swift typealias Complete = () throws -> Void let defaultComplete: Complete = {}
class Database { static var values: [String: String] = [:] static func insert(uuid: String, value: String, _ complete: Complete = {}) throws { print(“Insert: (uuid) value: (value)”) values[uuid] = value try complete() } static func delete(uuid: String, _ complete: Complete = {}) throws { print(“Delete: (uuid)”) if values[uuid] == nil { throw NSError.init(domain: “Err, delete - value at uuid: (uuid) does not exists”, code: 0) } values.removeValue(forKey: uuid) try complete() } } class Network { static func sync() throws { Swift.print(“sync”) if Bool.random() { throw NSError.init(domain: “Err, sync - unable to sync”, code: 0) } } } // insert do { try Database.insert(uuid: “1234”, value: “abc”, Network.sync) } catch { Swift.print(error.localizedDescription) } // delete do { try Database.delete(uuid: “1234”, Network.sync) } catch { Swift.print(error.localizedDescription) } // delete do { try Database.delete(uuid: “1234”, Network.sync) } catch { Swift.print(error.localizedDescription) } // Prints: // Insert: 1234 value: abc // sync // Delete: 1234 // sync // The operation couldn’t be completed. (Err, sync - unable to sync error 0.) // Delete: 1234 // The operation couldn’t be completed. (Err, delete - value at uuid: 1234 does not exists error 0.)
### 109. Wonders of OOP (Object oriented programming)
Neat trick to hock into subclass functionality
```swift
class A {
func update() {
insert() // Calls first B.insert not A.insert
}
func insert() {
print("A.insert()")
}
}
class B: A {
override func insert() {
print("B.insert()")
super.insert()
}
}
B().update() // Call B.insert() then A.insert() is called after
108. Overriding extension methods that has (parameter or return) with protocol types
- We prefix the protocol with @objc because we need to return this protocol type in “objc-override” calls
- We do this so that we can group related code in extensions. Rather than have classes with too much code
@objc protocol TextKind {
var text: String { get set }
}
class A {}
extension A {
@objc func getText() -> TextKind? {
print("A")
return nil
}
}
class B: A {}
extension B {
override getText() {
print("B")
return nil
}
}
_ = A().getText() // A
_ = B().getText() // B
107. Weakify closure variable
Usually we can use [weak self] in closurs, but not if its being attached to an event variable. Here is a workaround:
Service.onRemoteEvent = { data in
guard let self = Optional(self) else { return } // Weakify
update(self) // Use self safely here
}
106. Attaching a subtype to a protocol conformance
Setting the protocol type to CBManager directly wont compile. But using T with a type will
protocol StateUpdatable {
associatedtype T: CBManager // Declare an associated type `T` that must conform to `CBManager`
var manager: T { get } // Declare a variable `manager` of type `T`
}
class Central: StateUpdatable {
var manager: CBCentralManager = ... // CBCentralManager extends CBManager
}
class peripheral: StateUpdatable {
var manager: CBPeripheralManager = ... // CBPeripheralManager extends CBManager
}
105. Initiating an instance from an abstract class type
let baseType: NSTextField.Type = isSecure ? NSSecureTextField.self : NSTextField.self
let tf: NSTextField = baseType.init(frame: .init(origin: .zero, size: .init(width: 200, height: 24)))
104. Mouse position in an NSView for macOS
extension NSView {
/**
* Mouse point
* - Note: window.mouseLocationOutsideOfEventStream can also work as relativeToWin point
*/
var mousePoint: CGPoint {
let relativeToWin = self.window?.convertPoint(fromScreen: NSEvent.mouseLocation) ?? .zero // Try to convert the mouse location from the screen coordinate system to the window coordinate system, or use `.zero` if the window is nil
return self.convert(relativeToWin, from: nil) // Convert the point from the window coordinate system to the view's coordinate system and return it
}
}
103. Differentiating on typealias tuple
A simple concept to diff on tuples. Useful for making mixed search queries etc.
typealias A = (type: String, id: String)
typealias B = (type: String, label: String)
let x: Any = (type: "", label: "")
if x is A {
print("A")
} else if x is B {
print("B")
}
// Prints "B"
102. Overriding rawValue enum case
Great for supporting localization efforts etc.
enum Test: CaseIterable {
case a,b,c
}
extension Test {
init?(rawValue: String) {
}
var rawValue: String {
switch self {
case .a: return "A"
case .b: return "B"
case .c: return "C"
}
}
}
Test.allCases.forEach {
print($0.rawValue) // "A", "B", "C"
}
101. Reduce into:
Reduce trickery: (https://stackoverflow.com/a/43429063/5389500)
[0, 1, 1, 0].reduce(into: "") { $0 += $1 } // "0110"
...
100. Traversing view hierarchy
Traverses the entire UIView hierarchy downwards and collects views that are of specific type
public func descendants<T>(type: T.Type? = nil) -> [T] {
self.subviews.flatMap { $0.subviews.isEmpty ? [$0 as? T].compactMap { $0 } : $0.descendants(type: type) }
}
99. Remove first item in an array
extension Array {
/**
* Remove first item that match some criteria
* - Note: fileprivate is used because private won't work because we are in the Array scope
* ## Examples:
* uuids.removeFirst(closure: { $0 == uuid })
*/
@discardableResult fileprivate mutating func removeFirst(closure: (Element) -> Bool) -> Element? {
guard let i: Int = self.firstIndex (where: { closure($0) }) else { return nil } // Try to get the index of the first element in the array that satisfies the closure, return nil if it does not exist
return self.remove(at: i) // Remove the element at the specified index and return it
}
}
98. Assert internet:
/**
* Checks to see if internet is reachable
* ## Example:
* Self.checkNetwork { Swift.print("Net: \($0)") }
* - Fixme: Add result? to print error etc? or just throw error?
* - Fixme: Add semaphore with timeout as well
*/
static func checkNetwork(completionHandler: @escaping (_ internet: Bool) -> Void) {
DispatchQueue.main.async {
let url: URL = .init(string: "https://www.apple.com/")! // Create a URL object from the specified string
let request: URLRequest = .init(url: url) // Create a URL request object from the URL object
let task = URLSession.shared.dataTask(with: request) {data, response, error in // Create a data task with the URL request
if error != nil { // Check if there is an error
Swift.print("Error: \(String(describing: error))") // If there is an error, print the error message
completionHandler(false) // Call the completion handler with a `false` value
} else if let httpResponse = response as? HTTPURLResponse { // If there is no error, check if the response is an HTTP URL response
if httpResponse.statusCode == 200 { completionHandler(true) } // If the status code is 200, call the completion handler with a `true` value
else { print("Status-code: \(httpResponse.statusCode)") } // If the status code is not 200, print the status code
}
}
task.resume() // Start the data task
}
}
97. Comparing class types
class A: X {}
class B: X {}
class X {}
let b: X = B()
print(type(of: b.self))
let types: [X.Type] = [A.self, B.self]
print(types[1]) // B
print(type(of: b)) // B
print(type(of: b) == types[1]) // true
96. Instantinating from an array of class types
class BaseType {
required init(frame: CGRect) {}
}
class A: BaseType {}
class B: BaseType {}
class C: BaseType {}
let types: [BaseType.Type] = [A.self, B.self, C.self]
types.forEach {
let instance = $0.init(frame: .zero)
}
95. Calling apple async methods:
- If your asynchronous work needs to be waited for, you don’t have much of a choice but to mark your current code as also being async so that you can use await as normal. However, sometimes this can result in a bit of an “async infection” – you mark one function as being async, which means its caller needs to be async too, as does its caller, and so on, until you’ve turned one error into 50.
- In this situation, you can create a dedicated Task to solve the problem. We’ll be covering this API in more detail later on, but here’s how it would look in your code:
func doAsyncWork() async { print("Doing async work") } func doRegularWork() { Task { await doAsyncWork() } } doRegularWork() // Tasks like this one are created and run immediately. We aren’t waiting for the task to complete, so we shouldn’t use await when creating it.
94. Converting one dictionary type to another
let dict: [String, Any] = [:]
let newDict: [String: String] = dict.compactMapValues { $0 as? String }
93. Closure that throws
Sometimes it’s useful to be able to throw through a closure:
func someMethod() throws -> String { "works" }
var closure: () throws -> Void {}
closure {
print(try someMethod())
}
try closure() // works
92. Remove first where
extension Array {
/**
* Remove first item that match some criteria
*/
@discardableResult mutating func removeFirst(closure: (Element) -> Bool) -> Element? {
guard let i: Int = self.firstIndex (where: { closure($0) }) else { return nil }
return self.remove(at: i)
}
}
91. Customizable singleton
- Normal usage in production code:
SomeClass.shared// instance - Test usage:
SomeClass.sharedInstance(isTestMode: true)// test instance ```swift public static let shared: SomeClass = .sharedInstance() // with default customization private static var _shared: SomeClass? // One source of truth /** -
- Note: Use this directly if this singleton needs to be customized (Call it only once in the beginning of the code, use regular .shared in subsequent calls etc)
-
- Important: ⚠️️ Reference this in the code before .shared is referenced or it wont work */ public static func sharedInstance(isTestMode: Bool = false) -> SomeClass { guard let shared = _shared else { // if nil -> first run let shared = SomeClass(isTestMode: isTestMode) // Temp variable _shared = shared // Set permanent variable return shared } return shared // Instance already exist, return instance } ```
90. Handy way to generate uuid’s
In terminal we can do: uuidgen output: 1745B9C9-A369-4FD7-1EDF-B3AE2C268047
let uuid = UUID().uuidString // 2C432AEC-14A9-4F83-9ABB-60C6A7D948E7
Or of a custom length with: (Change 4 to get longer strings)
cat /dev/urandom | LC_CTYPE=C tr -dc 'a-zA-Z0-9' | head -c 4; echo
89. Manipulating values in a Dictionary
Manipulate key and value
let newDict = Dictionary(uniqueKeysWithValues: oldDict.map { key, value in (key.uppercased(), value.lowercased()) })
88. Debugging main / background thread
Great when working with network-IO and UI, since UI must happen on main thread and network usually on background.
print("Thread.isMainThread: \(Thread.isMainThread)") // true / false
87. Weak self in a method
Weak self can be used in methods, not just closures
func myInstanceMethod() {
weak var _self = self // Declare a weak reference to `self`
func nestedFunction(result : Bool) { // Declare a function `nestedFunction` that takes a boolean parameter `result`
_self?.anotherInstanceMethod() // Call the `anotherInstanceMethod` method on the weak reference to `self`
}
functionExpectingClosure(nestedFunction) // Call the `functionExpectingClosure` function with the `nestedFunction` closure as a parameter
}
86. Intersection of two arrays
We can also use Set to achieve intersection between arrays see stackoverflow
func intersection(a: [String], b: [String]) -> [String] {
a.filter { character in
b.contains(where: { character == $0 })
}
}
85. Use deinit to clean up or cancel callbacks
class Test {
deinit {
print("deinit")
// cancel callbacks etc
}
}
var test: Test? = Test()
test = nil // prints deinit
84. Compare equality between two instance of type Any
/**
* A hack to compare any
*/
fileprivate extension Equatable {
/**
* Equate two values of unknown type.
* ## Examples
* let bool: Any = Bool.random()
* AnyHashable.equate(bool, bool) // true
*/
static func equate(_ any0: Any?, _ any1: Any?) -> Bool {
if any0 == nil && any1 == nil { return true } // Check if both `any0` and `any1` are nil, return true if they are
guard
let equatable0 = any0 as? Self, // Try to cast `any0` to `Self`
let equatable1 = any1 as? Self // Try to cast `any1` to `Self`
else { return false } // If either cast fails, return false
return equatable0 == equatable1 // Return the result of the equality comparison between `equatable0` and `equatable1`
}
}
83. Forced unwrap with context
istead of unwrapping and getting no useful info if the value is nil, use fatalError instead.
let someValue: Int? = 0
let value = someValue ?? { fatalError("Integer missing") }()
82. Simpler error for Result
Sometimes you just want to read the error instead of switching
extension Result {
public func error<T>() -> T? where T: Error {
guard case .failure(let error) = self else { return nil }
return error as? T
}
}
enum DataReceivedError: Error { case offline, denied } // Declare an enumeration `DataReceivedError` that conforms to `Error` and has two cases: `offline` and `denied`
typealias OnDataReceived = (Result<String, DataReceivedError>) -> Void // Declare a type alias `OnDataReceived` for a closure that takes a `Result` object with a `String` value and a `DataReceivedError` error as parameters and returns `Void`
var onDataReceived: OnDataReceived = { result in // Declare a variable `onDataReceived` of type `OnDataReceived` and assign a closure that takes a `Result` object with a `String` value and a `DataReceivedError` error as a parameter
guard value = try? result.get() else { print("Err: \(result.error?.localizedDescription)") } // Try to get the value from the `Result` object, print the error message if it fails
print("content: \(value)") // Print the value if it succeeds
}
onDataReceived(.success("some content"), nil) // Call the `onDataReceived` closure with a `success` case and a `nil` error value
onDataReceived(.failure(.offline)) // Call the `onDataReceived` closure with a `failure` case and an `offline` error value
81. Handy UIAlertController shortcuts:
Simplifies calling UIAllertController
// Extension:
extension UIAlertController {
// Create a static function `alertOnError` that takes an error object and an optional closure as parameters and returns a UIAlertController object with an error title and message, and an OK button action that calls the closure if it is not nil
static func alertOnError(_ error: Swift.Error, handler: ((UIAlertAction?) -> Void)? = nil) -> UIAlertController {
let alert = UIAlertController(title: "Error", message: error.localizedDescription, preferredStyle: UIAlertController.Style.alert)
alert.addAction(UIAlertAction(title: "OK", style: UIAlertAction.Style.default, handler: handler))
return alert
}
// Create a static function `alertOnErrorWithMessage` that takes a message string and an optional closure as parameters and returns a UIAlertController object with an error title and the specified message, and an OK button action that calls the closure if it is not nil
static func alertOnErrorWithMessage(_ message: String, handler: ((UIAlertAction?) -> Void)? = nil) -> UIAlertController {
let alert = UIAlertController(title: "Error", message: message, preferredStyle: UIAlertController.Style.alert)
alert.addAction(UIAlertAction(title: "OK", style: UIAlertAction.Style.default, handler:handler))
return alert
}
// Create a static function `alertWithMessage` that takes a message string and an optional closure as parameters and returns a UIAlertController object with an alert title and the specified message, and an OK button action that calls the closure if it is not nil
static func alertWithMessage(_ message: String, handler: ((UIAlertAction?) -> Void)? = nil) -> UIAlertController {
let alert = UIAlertController(title: "Alert", message:message, preferredStyle: UIAlertController.Style.alert)
alert.addAction(UIAlertAction(title: "OK", style: UIAlertAction.Style.default, handler:handler))
return alert
}
}
// Usage:
let err = NSError(domain: "err", code: 0) // Create an NSError object with the specified domain and code
let closure = { (_ action: UIAlertAction?) in print(action) } // Declare a closure that takes an optional UIAlertAction object as a parameter and prints it
UIAlertController.alertOnError(err, closure).present() // Call the `alertOnError` static function on the UIAlertController class with the `err` object and the `closure` closure as parameters, and present the resulting UIAlertController object
UIAlertController.alertOnErrorWithMessage("Uh oh", closure).present() // Call the `alertOnErrorWithMessage` static function on the UIAlertController class with the `"Uh oh"` message string and the `closure` closure as parameters, and present the resulting UIAlertController object
UIAlertController.alertWithMessage("Open the bay doors?", closure).present() // Call the `alertWithMessage` static function on the UIAlertController class with the `"Open the bay doors?"` message string and the `closure` closure as parameters, and present the resulting UIAlertController object
80. Overriding computed variable in an extension
It’s nice to be able to put non stored variables in extensions
class A {}
extension A {
@objc var data: String { "a" }
}
class B: A {}
extension B {
override var data: String { "b" }
}
print(A().data) // a
print(B().data) // b
79. guard continue in a for loop
for item in items {
guard item.uuid == uuid else { continue } // skip this loop iteration
print("found matching uuid: \(item.uuid)")
guard item.data.count > 0 { continue } // skip items that doesn't have data
print("data.count: \(data.count)")
}
78. guard continue
We mostly use guard return. But there is also guard continue.
let str = "abc"
guard str == "abc" else { print("str is not abc"); continue }
77. Disabling some code for swift lint
Instead of disabling swift lint rules to avoid excessive xCode warnings you can disable small parts of the code:
// swiftlint:disable pattern_matching_keywords
case .detail(let acc, let mode): gotTo(view: view, account: acc, mode: mode)
// swiftlint:enable pattern_matching_keywords
76. Traversing descendants
/**
* Traverses the entire UIView hierarchy downwards and collects views that are of specific PARAM: type
*/
public func descendants<T>(type: T.Type? = nil) -> [T] {
self.subviews.flatMap { $0.subviews.isEmpty ? [$0 as? T].compactMap { $0 } : $0.descendants(type: type) }
}
75. Guard that throws
Nice way to provide info regarding why a function didn’t return the expected result etc
func someFunc(toggle: Boolean) -> String throws {
guard toggle else { throw NSError(domain: "err", code: 0) }
return "someString"
}
try ? someFunc(toggle: true) // "someString"
try ? someFunc(toggle: false) // nil
74. Array and Identifiable:
public extension Array where Element: Identifiable {
// Declare a function `find` that takes an ID parameter and returns the first element in the array that has a matching ID, or nil if no element is found
func find(_ id: Element.ID) -> Element? {
self.first { $0.id == id }
}
// Declare a function `findIndex` that takes an ID parameter and returns the index of the first element in the array that has a matching ID, or nil if no element is found
func findIndex(_ id: Element.ID) -> Int? {
self.firstIndex { $0.id == id }
}
// Declare a mutating function `remove` that takes an ID parameter and removes all elements from the array that have a matching ID
mutating func remove(_ id: Element.ID) {
self.removeAll { $0.id == id }
}
}
73. Switch on instance type:
Nice way to switch on types etc.
class A {}
class B {}
let val: Any = B()
switch val {
case is A:
print("A")
case is B:
print("B")
default:
print("nothing")
}
// B
72. Struct and dictionary conversion:
extension Encodable {
// Declare a computed property `dict` that returns a dictionary representation of the object, or nil if the object cannot be encoded as JSON data or deserialized as a dictionary
public var dict: [String: Any]? {
guard let data = try? JSONEncoder().encode(self) else { return nil } // Try to encode the object as JSON data, return nil if it fails
return (try? JSONSerialization.jsonObject(with: data, options: .allowFragments)).flatMap { $0 as? [String: Any] } // Try to deserialize the JSON data as a dictionary, return nil if it fails
}
// Declare an initializer `init` that takes a dictionary parameter and throws an error if the object cannot be decoded from the dictionary
public init(dict: [String: Any]) throws {
self = try JSONDecoder().decode(Self.self, from: JSONSerialization.data(withJSONObject: dict)) // Try to decode the object from the dictionary, throw an error if it fails
}
}
struct Job: Codable { let number: Int, name: String, client: String } // Declare a struct `Job` that conforms to `Codable` and has three properties: `number`, `name`, and `client`
let job: Job = .init(number: 1234, name: "Awards Ceremony", client: "ACME Productions") // Create a `Job` object with the specified properties
let dict: [String: Any] = job.dict ?? [:] // Convert the `Job` object to a dictionary, or an empty dictionary if the conversion fails
let clone = try? Job(dict: dict) // Try to create a new `Job` object from the dictionary, or nil if the creation fails
print("\(job == clone ? "✅" : "🚫")") // ✅
71. Setting a value with a key
class MyObject: NSObject{
@objc public var myString : String = "Not working"
}
func test(){
let value = "It works!"
let member = "myString"
let myObject = MyObject()
myObject.setValue(value, forKey: member)
print("New value: \(myObject.myString)")
}
70. Loop through struct with reflection
/**
* Creates dictionary of struct
* - Parameter instance: instance of struct
* - Returns: Dictionary with key value
*/
static func dict<T>(instance: T) -> [String: Any] {
let mirror = Mirror(reflecting: instance) // Create a mirror object for the specified instance
let keysWithValues = mirror.children.compactMap { (label: String?, value: Any) -> (String, Any)? in // Get the children of the mirror object, filter out any children with a nil label, and return a tuple of the label and value for each child
guard let label = label else { return nil } // If the label is nil, return nil
return (label, value) // Otherwise, return a tuple of the label and value
}
return Dictionary(uniqueKeysWithValues: keysWithValues) // Create a dictionary from the array of tuples, using the labels as keys and the values as values
}
69. Loop through struct / class properties:
This can also be done with mirroring
extension Encodable { var dictionary: [String: Any]? { // Declare a computed property `dictionary` that returns a dictionary representation of the object, or nil if the object cannot be encoded as JSON data or deserialized as a dictionary guard let data = try? JSONEncoder().encode(self) else { return nil } // Try to encode the object as JSON data, return nil if it fails return (try? JSONSerialization.jsonObject(with: data, options: .allowFragments)).flatMap { $0 as? [String: Any] } // Try to deserialize the JSON data as a dictionary, return nil if it fails } } struct Test: Encodable { let title: String = "this is title" let value: Int = 3 } let test = Test() test.dictionary?.forEach { (key, value) in print("key: \(key) value: \(value)") } // key: value value: 3 // key: title value: this is title
68. Sort with a more elaborate closure:
let closure: (_ a: Account, _ b: Account) -> Bool = { a, b in
if let a = a as? LoginItem, let b = b as? LoginItem {
return a.type < b.type
} else {
return a.date < b.date
}
}
return accounts.sorted(by: closure)
67. Find spm .build files
These folders are hidden, and adds size to projects. Find them with terminal. Then delete them
find . -name ".build"
66. Check equality between Arrays
This works when order of the array doesn’t matter ⚠️️ this might not work 😅
func isEqual(a: [String], b: [String]) -> Bool {
guard a.count == b.count else { return false } // Check if count is the same
return !a.contains { item in // Does it have a case where item isn't found in the other array
!b.contains { otherItem in // Does it have a case where item isn't found in the other array
item != otherItem
}
}
}
print(isEqual(a: ["1","2","3"], b: ["1","2","4"])) // false
print(isEqual(a: ["1","2","3"], b: ["1","2","3"])) // true
65: Operate on an array of class types
This can be useful for registering cell classes for instance
protocol Kind: AnyObject {}
class A: Kind {}
class B: Kind {}
extension Array where Element == Kind.Type {
func read() {
self.forEach { Swift.print("$0: \($0)") }
}
}
[A.self, B.self].read() // A, B
`
64: Make a struct mutable
struct X {
let a: String, b: Bool, c: Int
init(a: String, b: Bool, c: Int) {
self.a = a
self.b = b
self.c = c
}
}
extension X {
init(x: X, a: String? = nil, b: Bool? = nil, c: Int? = nil) { // the x contains the default values
self.a = a ?? x.a
self.b = b ?? x.b
self.c = c ?? x.c
}
}
let x1: X = .init(a: "test", b: true, c: 4)
Swift.print("x1: \(x1)") // X(a: "test", b: true, c: 4)
let x2: X = .init(x: x1, a: "lol")
Swift.print("x2: \(x2)") // X(a: "lol", b: true, c: 4)
let x3: X = .init(x: x2, b: false)
Swift.print("x3: \(x3)") // X(a: "lol", b: false, c: 4)
63: Insert after match
extension Collection {
/**
* ## Examples:
* let arr = ["a", "g", "r"]
* let idx = arr.insertionIndex(of: "m", using: <)
* rowData.insert("m", at: idx) // ["a", "g", "m", "r"]
*/
func insertionIndex(of element: Self.Iterator.Element, using areInIncreasingOrder: (Self.Iterator.Element, Self.Iterator.Element) -> Bool) -> Index {
firstIndex { !areInIncreasingOrder($0, element) } ?? endIndex
}
}
62: Remove duplicates from the array, preserving the items order
extension Array where Element: Hashable {
// Declare a function `filterDuplicates` that returns an array of unique elements from the original array, preserving their order
func filterDuplicates() -> Array<Element> {
var set = Set<Element>() // Create an empty set to store unique elements
var filteredArray = Array<Element>() // Create an empty array to store the filtered elements
for item in self { // Iterate over each element in the original array
if set.insert(item).inserted { // Try to insert the element into the set, and append it to the filtered array if it is unique
filteredArray.append(item)
}
}
return filteredArray // Return the filtered array
}
}
61: Getting indices of filtered array
extension Array where Element: Equatable {
/**
* items.indexes(of: "A") // [0, 2, 4]
* items.indexes(of: "B") // [1]
*/
func indexes(of element: Element) -> [Int] {
return self.enumerated().filter({ element == $0.element }).map({ $0.offset })
}
}
60: Performance testing:
/**
* - Note: Set a NSDate to measure the time like this: var startTime:NSDate = NSDate();abs(startTime!.timeIntervalSinceNow)
* - Note: Or even easier: let d = CACurrentMediaTime(); /*Do heavy computing*/let d1 = CACurrentMediaTime()-d; print(d1)//0.452 sec
* ## Examples:
* testPerformance("Adding styles took: "){CSSFileParser.cssString(url)}//Adding styles took 2.4secs
* - Parameter startTime: performance test start time
*/
func testPerformance(_ context: String = "", _ startTime: Date = Date(), _ closure:@escaping ()->Void) {
closure()/*Executes the closure*/
Swift.print(context + " \(abs(startTime.timeIntervalSinceNow))" + " Secs")/*Prints performance test end time*/
}
/**
* Allows you to test performance and also return a value
* ## Examples:
* let result:String = testPerformance{readData()}//0.028 Secs
*/
func testPerformance<T>(_ context: String = "", _ startTime:Date = Date(), _ closure:@escaping ()->T) -> T {
defer {/*execute just before code execution leaves the current block of code*/
Swift.print(context + " \(abs(startTime.timeIntervalSinceNow))" + " Secs")/*Prints performance test end time*/
}
return closure()/*Executes the closure*/
}
59: Fitting a size to a ratio:
/**
* Fits inside a frame (Scales to ratio)
* - Fixme: ⚠️ Add zoom method: Always fills a frame, ️do this laster
* - Note: Basically used to get a new size that fits inside size, and has the correct ratio
* ## Examples:
* fit(size: CGSize(width: 200, height: 200), ratio: 0.5) // CGSize(100, 200)
*/
static func fit(_ size: CGSize, ratio: CGFloat) -> CGSize{
let w: CGFloat = size.width // Get the width of the size
let h: CGFloat = size.height // Get the height of the size
if (w / h) > ratio { // Check if the width is wider than the ratio allows
return CGSize(height: h * ratio, height: h) // If so, return a new size with the height scaled to match the ratio and the original height
} else if (w / h) < ratio { // Check if the height is taller than the ratio allows
return CGSize(width: w, height: w * ratio) // If so, return a new size with the width scaled to match the ratio and the original width
} else {
return CGSize(width: w, height: h) // Otherwise, return the original size
}
}
58 For loops:
10++ different to for loop types:
for i in 0..4 {}👈 regular forward loopingfor (i, obj) in arr.enumerated() { print(i); print(obj) }👈 access to i and objfor obj in arr {}👈 iterate over objects (no access to original array)for i in (0..<4).reversed() {}👈 backward loopingvar i = 0; while(i < 4) { print(i); i += 1 }👈 If you want to manipulate i while loopingfor i in stride(from: 0, to: 10, skip: 2) {}👈 Skips every otherarr.forEach{$0}👈 Easiest for-loop but only if you don’t need to exit earlyfor i in arr.indices {print(i)}👈 Access to ifor _ in 0..<arr.count👈 If you just wan’t to loop something and not use any valuearr.reversed.forEach{$0}👈 reversed forEach, more functional 🤖 .map also works(0..<4).indices.map { i in return UIButton.init(frame: .zero) }👈 makes 4 buttons 🤖for (i, str):(Int, String) in strings.enumerated() { print(("\(i) and \(str)")) }👈 special for looparr.enumerated().forEach { (_ i: Int,_ str: Data) in print(("\(i) and \(str)")) }👈 👌
57 EitherOr
By adding more .random calls you decrease the chance of being false.
1/2, 1/4, 1/6, 1/8 etc
let eitherOr: Bool = !(Bool.random() && Bool.random()) // 1 in 4 is false
56 Autolayout across different subviews
Nice to know: If you ever want to use autolayout but need things to be above other elements etc. Autolayout works across subviews 👌
55 Better clamping:
/**
* Clamp
* ## Examples:
* CGFloat.clamp(val: 44, min: 33, max: 38) // 38
*/
static func clamp(val: CGFloat, min: CGFloat, max: CGFloat) -> CGFloat {
if val <= min { // under
return min
} else if val >= max { // over
return max
} else { // between
return val
}
}
54 Clamp a value between min and max
let value: CGFloat = 700
let lower: CGFloat = 200
let upper: CGFloat = 400
let clampedValue = max(lower, min(upper, value)) // 400
53 Reduce to total amount
let totalW: CGFloat = TabType.allCases.reduce(CGFloat(0)) {
$0 + itemWidth(text: $1.rawValue)
}
52 Capitalize first letter:
extension String {
/**
* ## Examples:
* let test = "the rain in Spain"
* print(test.capFirst()) // "The rain in Spain"
*/
var capFirst: String {
prefix(1).capitalized // Get the first character of the string and capitalize it
+ dropFirst() // Drop the first character of the string and return the rest
}
}
51 Fixed numbers:
let duration = String(format: "%.01f", 3.32323242) // 3.3
50 Simple diffing in swift:
let arrayA: [String] = ["a", "b", "c"]
let arrayB: [String] = ["c", "a", "d", "f", "g"]
// Find items in b that is not in a
let diff: [String] = arrayB.filter { item in
!arrayA.contains { item == $0 }
}
Swift.print("diff: \(diff)") // ["d", "f", "g"]
49: Init an enum
enum Apperance : String {
case Dark, Light
}
extension Apperance {
init() {
let type = UserDefaults.standard.string(forKey: "AppleInterfaceStyle") ?? "Light"
self = Apperance(rawValue: type)!
}
var inDarkMode: Bool {
let currentStyle = Apperance() // Create an instance of the `Apperance` class and assign it to the `currentStyle` constant
if case .Dark = currentStyle { // Check if the `currentStyle` is `.Dark`
return true // If so, return `true`
} else if case .Light = currentStyle { // Check if the `currentStyle` is `.Light`
return false // If so, return `false`
} else { // If the `currentStyle` is neither `.Dark` nor `.Light`
fatalError("Not supported") // Raise a fatal error with the specified message
}
}
}
48: Generic typealias
// Warning: ⚠️️ Generics does not work when overriding functions in extensions
typealias Parser<A> = (String) -> [(A, String)]
func parse<A>(stringToParse: String, parser: Parser)
46: Instead of opening playground. Use terminal to run some swift code
- All you do is open terminal. And write swift. copy paste any code and hit enter to run it.
while i < 4 { print("🎉") i += 1 }
45: Mark methods as deprecated and get warning:
- Document API changes with @available keyword.
- Great way to rename code without breaking backward compatibility, but at the same time motivating users to use the new api name, just make a typealias with the bellow code above it
- There is also
@available(*, deprecated)if something doesn’t have a replacement API call etc@available(*, deprecated, renamed: "newMethodName") // You can also point to new class : "UIAlertController.createAlert" func foo() { ... } // Each time foo() is called, a deprecation warning will appear: // foo is deprecated, renamed `newMethodName` // name things: allItems(SecClass:) if the type of the param is the only change etc
There is also:
@available(*, deprecated, message: "This closure will be removed in future version. Please use `handler`.")
44. Measure time consumed by a closure
/**
* Measures how long a closure takes to complete
* ## Examples:
* timeElapsed { sleep(2.2) } // 2.20000
*/
func timeElapsed(_ closure: () -> Void) -> Double {
let start = DispatchTime.now() // Get the current time
closure() // Call the closure
let end = DispatchTime.now() // Get the current time again
let diff = end.uptimeNanoseconds - start.uptimeNanoseconds // Calculate the difference between the two times in nanoseconds
return Double(diff) / 1_000_000_000 // Convert the difference to seconds and return it
}
43. Do many things simultaneously and call onComplete when things are done
For more complex scenarios see: https://github.com/eonist/parallelloops
/**
* - Abstract: process data in parallel on a background thread and calls a onComplete when it's complete
* ## Examples:
* processData { Swift.print("✅") } // Output: start, 1, 2, 0, 3, ✅
*/
func processData(onComplete: @escaping () -> Void) {
Swift.print("start") // Print "start"
DispatchQueue.global().async { // Dispatch a task asynchronously to a global queue
DispatchQueue.concurrentPerform(iterations: 4) { index in // Perform a task concurrently for the specified number of iterations
Swift.print("\(index)") // Print the index
sleep((1..<3).randomElement()!) // Wait for a random number of seconds between 1 and 3
}
onComplete() // Call the completion handler
}
}
42. Map ranges:
Creates an array of random numbers
func randInt() -> Int { return Int(arc4random()) }
let randomArray = (1...4).map { _ in randInt() } // 3,1,2,2
41. Use an online swift playground for quick tests:
http://online.swiftplayground.run
import Foundation
print("Hello World")
print((1...40).contains(1)) // true
print((1...40).contains(40)) // true
There is also terminal which can test swift code by typing swift and hitting enter
40. Flattening nested loops:
let width = 4
let height = 4
// nested loop
for y in (0..<height) { // Iterate over each row of the grid
for x in (0..<width) { // Iterate over each column of the grid
let index: Int = y * width + x // Calculate the index of the current cell
print("index: \(index)") // Print the index of the current cell
}
}
// flattening:
var x = 0 // Initialize the x-coordinate to 0
var y = 0 // Initialize the y-coordinate to 0
while x < width && y < height { // Loop while the x-coordinate is less than the width and the y-coordinate is less than the height
let index: Int = y * width + x // Calculate the index of the current cell
print("i: \(index)") // Print the index of the current cell
x += 1 // Increment the x-coordinate
if x == width { y += 1; x = 0 } // If the x-coordinate is equal to the width, increment the y-coordinate and reset the x-coordinate to 0
}
39. Accounting for iPhoneX notch
// Override the `viewDidAppear` method to adjust the view's frame to fit the screen's bounds, taking into account the safe area insets
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
view.frame = UIScreen.main.bounds.inset(by: view.safeAreaInsets)
}
// Override the `viewDidLoad` method to set the view to a custom `View` instance with a zero frame
override func viewDidLoad() {
super.viewDidLoad()
self.view = View(frame: .zero)
}
38. Store constant in array types
- Great way to store values in array types, or add custom methods to array types
- Allows you to get rid of clunky looking
Array where Element = SomeThingtypealias ColorMapItem = UIColor typealias ColorMap = [ColorMapItem] extension ColorMap { // Array where Element == ColorMapItem static let rainbow = [.blue, .red, .yellow] } let rainbowColors: ColorMaps = .rainbow
37. Structure colors:
import UIKit
/**
* ## Examples:
* Color.Text.header // white
* Color.UI.Background.secondary // lightGray
*/
// Define a nested `Color` struct with nested `Text` and `UI` structs, each containing static properties for various colors
struct Color {
struct Text {
static let header: UIColor = .white // The color for header text
static let button: UIColor = .systemBlue // The color for button text
static let description: UIColor = .lightGray // The color for description text
static let paragraph: UIColor = .gray // The color for paragraph text
static let title: UIColor = .white // The color for title text
}
struct UI {
struct Foreground {
static let primary: UIColor = .darkGray // The primary foreground color
static let secondary: UIColor = .gray // The secondary foreground color
}
struct Background {
static let primary: UIColor = .gray // The primary background color
static let secondary: UIColor = .lightGray // The secondary background color
}
}
}
36. Call the method in the alternating bool assert
- Imagine [r,g,b] are computational heavy methods
- The assert has to execute every method to assert
- By not pre-calling the methods before the group assert, you save cpu processing power
func r: Bool { print("r"); return true } func g: Bool { print("g"); return false } func b: Bool { print("b"); return true } let valid: Bool = r && g && b print(valid) // r,g false (skips calling b)
35. Using try with for loops
do {
try (1...40).forEach { qrVersion in
guard let qrVer = QRVer(rawValue: qrVersion - 1) else { throw NSError(domain: "unable to create qr-ver", code: 0) }
guard let data: Data = QRStringData.randomData(config: (qrVer, .byte, .l)) else { throw NSError(domain: "unable to make data", code: 0) }
guard let qrImage: Image = try? QRWriter.image(data: data, ecLevel: .l, moduleMultiplier: 16) else { throw NSError(domain: "unable to create UIImage", code: 0) }
guard let ciImg: CIImage = qrImage.ciImage ?? qrImage.ciImage else { throw NSError(domain: "err ciimg", code: 0) }
let symbolVersion: Int? = try? ciImg.symbolVersion()
guard qrVersion == symbolVersion else { throw NSError(domain: "version: \(qrVersion) failed", code: 0) }
}
Swift.print("All symbol versions checked out")
onComplete(true)
} catch {
Swift.print("error: \(error)")
onComplete(false)
}
34. let variables in functions
The bellow is possible because index is guaranteed to be set and is much more readable than using a closure to do the same thing.
func doSomething() {
let index: Int
if versionNumber <= 9 { index = 0 }
else if versionNumber <= 26 { index = 1 }
else { index = 2 }
}
33. Queue up things with DispatchGroup:
You can nest closures, but nesting is often a “code-smell”, using DispatchGroup and .wait can be a nice alternative.
typealias COMPLETION = () -> ()
func functionOne(completion: @escaping COMPLETION) {
print("1")
DispatchQueue.main.asyncAfter(deadline: .now() + 2.1) { completion() }
}
func functionTwo(completion: @escaping COMPLETION) {
print("2")
DispatchQueue.global(qos: .background).asyncAfter(deadline: .now() + 1) { completion() }
}
func functionThree(completion: @escaping COMPLETION) {
print("3")
DispatchQueue.main.asyncAfter(deadline: .now() + 0.6) { completion() }
}
DispatchQueue.global().async {
let dispatchGroup = DispatchGroup() // Create a new dispatch group
dispatchGroup.enter() // Enter the dispatch group
functionOne { dispatchGroup.leave() } // Call `functionOne` and leave the dispatch group when it completes
dispatchGroup.wait() // Wait for `functionOne` to complete, with a reasonable timeout
dispatchGroup.enter() // Enter the dispatch group again
functionTwo { dispatchGroup.leave() } // Call `functionTwo` and leave the dispatch group when it completes
dispatchGroup.wait() // Wait for `functionTwo` to complete, with a reasonable timeout
dispatchGroup.enter() // Enter the dispatch group again
functionThree { dispatchGroup.leave() } // Call `functionThree` and leave the dispatch group when it completes
dispatchGroup.wait() // Wait for `functionThree` to complete, with a reasonable timeout
dispatchGroup.notify(queue: .main) { // Notify the main queue when all tasks are completed
Swift.print("all done") // Print "all done"
}
} // this will print: 1, 2, 3, all done
32. “Switch” with additional guard clauses:
enum Flavours: String {
case vanilla, chocolate, strawberry
}
func makeIceCream(flavour: Flavours, caneType: String? = nil) {
if case .vanilla = flavour, let caneType = caneType {
print("Vanilla with \(caneType)")
} else if case .strawberry = flavour {
print("Strawberry")
} else if case .chocolate = flavour {
print("Chocolate")
} else {
print("No 🍦 for you")
}
}
makeIceCream(flavour: .vanilla, caneType: "Cane") // Vanilla with Cane
makeIceCream(flavour: .strawberry) // Strawberry
makeIceCream(flavour: .vanilla) // No 🍦 for you
31: Simulate network behaviour
Sleep for a random amount of time between 1 and 7 seconds. (Great for simulating async network calls etc)
sleep((1..<7).randomElement() ?? 1)
30. Recursive flatMap
/**
* Multidimensional-flat-map...because flatMap only works on "2d arrays". This is for "3d array's"
* - Note: A 3d array is an array structure that can have nested arrays within nested arrays infinite addendum
* - Note: Alternate names for this method as suggest by @defrenz and @timvermeulen on slack swift-lang #random: `recursiveFlatten` or `recursiveJoined`
* ## Examples:
* let arr:[Any] = [[[1],[2,3]],[[4,5],[6]]] 👈 3d array (3 depths deep)
* let x2:[Int] = arr.recursiveFlatmap()
* Swift.print(x2)//[1,2,3,4,5,6]
*/
func recursiveFlatmap<T>() -> [T] {
var results = [T]()
for element in self {
if let sublist = element as? [Self.Iterator.Element] { // Check if the element is an array
results += sublist.recursiveFlatmap() // If so, recursively call `recursiveFlatmap` on the sublist and append the results to the `results` array
} else if let element = element as? T { // Otherwise, check if the element is of type `T`
results.append(element) // If so, append the element to the `results` array
}
}
return results
}
29. Access name of int enum:
This does not work on some native enums, often due to the fact that they are Objc enums, In such cases make an extension that has a switch that returns the name.
public enum TestEnum : Int {
case one = 0, two, three
}
Swift.print("\(String(describing: TestEnum.three))") // three
// or another example:
public enum FocalType: Int, CaseIterable { case ultraWide, wide, tele }
print(FocalType.allCases.map { "\($0): \($0.rawValue)" }.joined(separator: ", "))
// ultraWide : 0, wide : 1, tele : 2
28. Long numbers:
//Bad
let valA: Int = 100000000 * 2
//Good:
let valB: Int = 100_000_000 * 2
27. Prefer contains over first
// Good
arr.first(where: { $0 == match }) != nil
// Better:
arr.contains(where: { $0 == match })
// Best
arr.contains { $0 == match }
26. Visual colors in xCode
A nice way to have visual representation of colors in code:
enum Colors {
static let teal: UIColor = #colorLiteral(red: 0, green: 0.8039215686, blue: 0.8039215686, alpha: 1)
static let lightTeal: UIColor = #colorLiteral(red: 0.6, green: 1, blue: 0.3921568627, alpha: 1)
static let darkTeal: UIColor = #colorLiteral(red: 0, green: 0.6, blue: 0.6, alpha: 1)
}
// Colors.teal
25. Optional chaining
Swift.print(Optional("✅") ?? "🚫") // 🚫
Swift.print(Optional(nil) ?? "🚫") // ✅
It’s like providing a default value if the optional is nil. You can do. it’s equivalent to doing Optional("") != nil ? Optional("") : ""
24. Make rounded graphics look great
- Use
NSScreen.main.backingScaleFactorfor macOS andUIScreen.main.scalefor iOS - This ensures that rounded graphics looks sharp
self.caLayer?.rasterizationScale = 2.0 * Screen.mainScreenScale
self.caLayer?.shouldRasterize = true
23. Make methods off-limit
https://www.mokacoding.com/blog/swift-unavailable-how-to/
This is a great way to avoid having to repeat this method in every subclass that uses :UIView
@available(*, unavailable)
public required init?(coder: NSCoder) {
fatalError("init?(coder:) is not supported")
}
22. Avoid xCode warning when returned value is not used:
@discardableResult
func add(a: Int, b: Int) -> Int {
return a + b
}
21. Store reuse identifiers in a cell extension
There is also a small library that simplifies the registry and reuse syntax: https://github.com/eonist/ReusableCell
class SomeTableViewCell: UITableViewCell {} // Define a `SomeTableViewCell` class that inherits from `UITableViewCell`
extension SomeTableViewCell {
static let cellReuseIdentifier: String = "\(SomeTableViewCell.self)" // Define a static property `cellReuseIdentifier` that returns the class name as a string
}
20. Flattening 3d array:
See also tip nr.40: Flattening nested loops:
struct Subscription { let type: String }
struct Account { let subscriptions: [Subscription] }
struct User { let accounts: [Account] }
let users: [User] = [
User(accounts: [Account(subscriptions: [Subscription(type: "a")])]),
User(accounts: [Account(subscriptions: [Subscription(type: "b")]),Account(subscriptions: [Subscription(type: "c")])]),
User(accounts: [Account(subscriptions: [Subscription(type: "d"), Subscription(type: "e"), Subscription(type: "f")])])
]
// Not preferred:
let result1 = users.map { user in // Map over each user in the `users` array
return user.accounts.map { account in // Map over each account in the user's `accounts` array
return account.subscriptions.map { subscription in // Map over each subscription in the account's `subscriptions` array
return subscription.type // Return the subscription type
}
}
}.flatMap{ $0 }.flatMap { $0 } // Flatten the nested arrays into a single array of subscription types
Swift.print("result1: \(result1)")//["a", "b", "c", "d", "e", "f"]
// Preferred
let result2 = users.flatMap { $0.accounts }.flatMap { $0.subscriptions }.flatMap{ $0.type }
Swift.print("result2: \(result2)")//["a", "b", "c", "d", "e", "f"]
19. Dot-syntax inference and array iteration with Enums
/**
* TIPS: Access all colors via: Constants.Colors.allCases
* ## Examples: Constants.Colors.allCases[1]//UIColor.yellow
* ## Examples: Constants.Colors.red//UIColor.red
* - Important: ⚠️️ the key must be unique and the the value must be unique
*/
class Constants{
enum Colors: String, CaseIterable {
case blue = "FB1B4D", yellow = "1DE3E6", red = "22FFA0", green = "FED845"
var uiColor: UIColor {
return UIColor.init(hex: self.rawValue)
}
}
}
18. Combinational types instead of generics
The setCardConstraints method requires conformance to UIView and ConstraintKind
// Generics
func setCardConstraints<T: UIView>(card: T) where T: ConstraintKind { // 👈 Looks messy
card.applyConstraint{ view in
// do stuff
}
}
// Combination type:
public typealias UIViewConstraintKind = UIView & ConstraintKind
func setCardConstraints(card: UIViewConstraintKind) { // 👈 Looks much cleaner
card.applyConstraint{ view in
// do stuff
}
}
17. Delay something
DispatchQueue.main.asyncAfter(deadline: .now() + 4) {
// Do something after 4 seconds have passed
}
// Alternatively:
DispatchQueue.global(qos: .background).async { // asyncAfter also works here, instead of sleep
sleep(4)
print("Active after 4 sec, and doesn't block main")
DispatchQueue.main.async {
// Do stuff in the main thread here
}
}
// Alternatively:
let second: Double = 1000000
usleep(useconds_t(0.002 * second)) // will sleep for 2 milliseconds (.002 seconds)
// Alternatively:
/**
* Supports fractional time
* ## Examples:
* sleep(sec: 2.2) // sleeps for 2.2 seconds
*/
public func sleep(sec: Double){
usleep(useconds_t(sec * 1000000)) // wait for n secs
}
// Pausing in a loop:
let array = [1, 2, 3]
DispatchQueue.global(qos: .background).async { // Dispatch a task asynchronously to a global queue with a background quality of service
array.forEach { i in // Iterate over each element in the `array`
sleep(1) // Sleep for 1 second
DispatchQueue.main.async { // Dispatch a task asynchronously to the main queue
Swift.print("i: \(i)") // Print the current element of the `array`
}
}
}
16. Enums in a closure to describe events
class MyViewController {
enum Error: Swift.Error {
case invalidUsername
case invalidPassword
}
enum Event {
case loginSuccess
case showErrorMessage(Error) // - showErrorMessage: We errored, we need to show an error message
}
typealias EventAction = (Event) -> Void
var eventHandler: EventAction?
func login(name: String, password: String) {
guard "test" == user.password else {
eventHandler(.showErrorMessage(.invalidUsername))
return
}
guard "Monica" == user.name else {
eventHandler(.showErrorMessage(.invalidUsername))
return
}
eventHandler(.loginSuccess)
}
}
func handler(event: Event) {
switch event {
case .loginSuccess:
print("user logged in")
case .showErrorMessage(let error):
print("user did not log in, reason: \(error.description)")
}
}
let controller = MyViewController()
controller.eventHandler = handler
controller.login(name: "John", password: "abc123")
15. Rethrows:
The rethrows keyword indicates to the compiler that the outer function is a throwing function only if the closure passed in throws an error that is propagated to the current scope. Basically with rethrows, we can use throw inside the closure. When the error handlers are called within the function we use throws.
typealias MagicalOperation = () throws -> MagicalResult
func doSomethingMagical(magicalOperation: MagicalOperation) rethrows -> MagicalResult {
return try magicalOperation()
}
14 Use custom closures with the native sortedBy method:
enum CardType {
case heart, spades, diamond, clover
}
enum CardValue{
case two, three, four, five, six, seven, eight, nine, ten, prince, queen, king, ace
}
typealias Card = (type: CardType, value: CardValue)
typealias Sorter = ((_ element1: Card, _ element2: Card) -> Bool)
// arrayTest
func arrayTest(){
let someCards: [Card] = [(.spades, .eight), (.heart, .seven), (.heart, .king), (.diamond, .ace), (.heart, .two)]
let findHearts: [Card] = someCards.filter { return $0.type == .heart }
Swift.print("unsorted.🔵")
findHearts.forEach { (card: Card) in
Swift.print("card.type: \(card.type) card.value: \(card.value)")
}
Swift.print("unsorted.🔴")
let sorter: Sorter = { (element1, element2) -> Bool in
return element1.value.hashValue < element2.value.hashValue
}
let sortedHearts = findHearts.sorted { sorter($0, $1) } // sort the cards
Swift.print("sorted.🔵")
sortedHearts.forEach { Swift.print("$0.type: \($0.type) $0.value: \($0.value)") } // print the cards
Swift.print("sorted.🔴")
}
13 Manipulate an object in a closure
@discardableResult // 👈 Avoids XCode compiler warnings if result is not used
func with<T>(_ item: T, update: (inout T) throws -> Void) rethrows -> T {
var item = item
try update(&item)
return item
}
//EXAMPLE 1:
let rectangle: CGRect = with(.init(x: 0, y: 0, width: 100, height: 100)) {
$0 = $0.offsetBy(dx: 20, dy: 20)
$0 = $0.insetBy(dx: 10, dy: 10)
}
Swift.print(rectangle) // X:30.0, y:30.0, width:80.0, height:80.0
//EXAMPLE 2:
let color = with(UIColor.init(red: 50, green: 100, blue: 0, alpha: 0.9)) { ( col:inout UIColor) -> Void in
col = col.withAlphaComponent(0.2)
}
Swift.print(color.cgColor.alpha) // 0.2
https://github.com/eonist/with
12. Result (for async callback returns)
⚠️️ write result example with the try catch inline trick, and remove the bellow etc
⚠️️ improve this: ⚠️️
enum Result<Value> {
case success(Value)
case failure(Swift.Error)
}
func start(_ completionHandler: @escaping (Result<Any>) -> Void) -> FBSDKGraphRequestConnection{
return start() { (_, response, error) in // Call the `start` method with a completion handler that takes a tuple of optional `URLResponse`, optional `Error`, and no return value
switch (response, error) { // Use a tuple pattern matching to check the response and error
case (.some(let result), .none): // If the response is not `nil` and the error is `nil`
completionHandler(Result(value: result)) // Call the completion handler with a `Result` instance containing the response
case (.none, .some(let error)): // If the response is `nil` and the error is not `nil`
completionHandler(Result(error: error)) // Call the completion handler with a `Result` instance containing the error
case (.none, .none), (.some, .some): // If both the response and error are `nil` or both are not `nil`
preconditionFailure("Unexpected State") // Raise a runtime error
}
}
}
switch result {
case .success (let value as [ String : Any ]) where value["email"] is String:
let email = value["email"] as! String
print("email: \(email)")
default:
self.present(error: Error(.facebookOther))
}
https://stackoverflow.com/questions/51235876/swift-pattern-matching-switch-downcasting-and-optional-binding-in-a-single-s
11. Code injection via Protocol extension
protocol FruitKind {
func eat() // Class must implement doSomething
}
extension FruitKind {
func eat() { print("Tastes like fruit") } // default implementation
}
protocol AppleKind: FruitKind {} // inherit base protocol
extension AppleKind {
func eat() { print("Tastes like 🍎") }// override default implementation
}
protocol PearKind: FruitKind {} // inherit base protocol
extension PearKind {
func eat() { print("Tastes like 🍐") }// override default implementation
}
class Fruit: FruitKind {} // Make a class
extension Fruit: AppleKind {} // 👈 you sort of attach custom apple functionality
let fruit = Fruit() // create an instance of Class
fruit.eat() // Tastes like 🍎 (calls the AppleKind.eat instead of Fruit.eat and prints)
class AnotherFruit: FruitKind {}
extension AnotherFruit: PearKind {} // 👈 you sort of attach custom pear functionality
let anotherFruit = AnotherFruit()
anotherFruit.eat() // Tastes like 🍐 (calls the AppleKind.eat instead of Fruit.eat and prints)
10. Nifty array trick:
let result:[String] = Array(repeating: "🎉", count: 3)
print(result) // 🎉🎉🎉
/**
* ## Examples: Margin.bottom.rawValue//32
* Margin.allCases[1].rawValue//32
* - Note: values must be unique
*/
enum Margin: CGFloat, CaseIterable{
case top = 24, bottom = 32, horizontal = 12
}
9. Closure Generics
typealias UIViewConstraintKind = UIView & ConstraintKind // This works almost like someValue:T .... where T:ConstraintKind
typealias ReturnType = (anchor: AnchorConstraint, size: SizeConstraint) // This just makes the method that returns this simpler
typealias ConstraintKindClosure = (_ view: UIViewConstraintKind) -> ReturnType
/**
* NOTE: We use the "combination-type": `UIViewConstraintKind` since closures can't do regular generics like t:UIView where Self:ConstraintKind
*/
func activateConstraintKind(closure: ConstraintKindClosure) {
let constraints:ReturnType = closure(self) // the constraints is returned from the closure
//...do something with the constraints
}
8. Accessing raw and hashValue of enum
enum CellType: String {
case primary, secondary, tierary
}
let possibleCellType = CellType(rawValue: "tierary")
possibleCellType // tierary
possibleCellType?.hashValue // 2
7. String enum’s
No need to hard code the string, as long as the enum type is string 👌, the name is auto converted to string when you call rawValue
enum CellType: String {
case primary, secondary, tierary
}
print("\(CellType.primary.rawValue)") // primary
print("\(CellType.tierary.rawValue)") // tierary
6. Override static variable
class var id : String { return "\(HorCell.self)" } // In a class
override class var id : String { return "\(PrimaryCell.self)" } // In a sub-class of the class
5. Action as argument
In the case bellow we use an argument to assign the target. It could be possible to pass a ref to the buttonTouched method as well. Example of that comming soon.
func createBtn(action: String) -> UIButton {
let btn: UIButton = .init(type: .system)
btn.addTarget(self, action: Selector(action), for: .touchUpInside)
return btn
}
@objc func buttonTouched(_ sender: UIButton) {
Swift.print("buttonTouched")
}
let btn = createButton(action: "buttonTouched:") // 👈 The : character is important
4. Simplify similar code with a closure
let closure = { (text: String, bgColor: UIColor, y: CGFloat, action: String) in
let btn: UIButton = .init(type: .system) // Create a new `UIButton` instance with the system type
btn.backgroundColor = bgColor // Set the background color of the button to `bgColor`
btn.setTitle(text, for: .normal) // Set the title of the button to `text` for the normal state
btn.titleLabel?.font = .systemFont(ofSize: 12) // Set the font of the button's title label to a system font with size 12
btn.frame = .init(x:00, y:y, width:100, height:50) // Set the frame of the button to a new `CGRect` instance with the specified values
btn.addTarget(self, action: Selector(action), for: .touchUpInside) // Add a target-action pair for the `.touchUpInside` control event
self.addSubview(btn) // Add the button as a subview of the current view
}
// btn1
closure(
"Forward",
.gray,
250,
"onForwardButtonClick"
)
// btn2
closure(
"Back",
.lightGray,
250,
"onbackButtonClick"
)
3. Asserting if an array index exist:
let arr = [1, 2, 3]
if let fourthItem = (3 < arr.count ? arr[3] : nil ) {
Swift.print("fourthItem: \(fourthItem)")
} else if let thirdItem = (2 < arr.count ? arr[2] : nil) {
Swift.print("thirdItem: \(thirdItem)")
}
// Output: thirdItem: 3
2. Simple Caching:
/**
* Also works for external server data
* ## Examples: if let data = myBigData { print(data) }
*/
private var _myBigData : Data? = nil
var myBigData : Data? {
set {
self._myBigData = newValue
} get {
if _myBigData == nil {
// ... get a reference to file on disk, f ...
if let d = try? Data(contentsOf:f) {
self._myBigData = d
// ... erase the file ...
}
}
return self._myBigData
}
}
1. Sometimes using switch can be overkill:
enum State {
case a, b, c
}
let state: State = .b
if [.a, .b].contains(state) {
Swift.print("either a or b")
}else if case .a = state {
Swift.print("must be c")
}