John Sundell JohnSundell

iOS development freelancer, and creator of Swift by Sundell. I build apps, games and Swift developer tools.

JohnSundell / Autoclosure.swift

Created January 19, 2017 15:00

Simple Dictionary extension to avoid the if let-dance when retrieving values

	extension Dictionary {
	mutating func value(for key: Key, orAdd closure: @autoclosure () -> Value) -> Value {
	if let value = self[key] {
	return value
	}

	let value = closure()
	self[key] = value
	return value
	}

JohnSundell / TestingMemoryManagement.swift

Created January 25, 2017 11:15

Sample on how you can easily test your memory management in Swift

	class Cache<T> {
	private lazy var objects = [String : T]()

	func object(forKey key: String) -> T? {
	return objects[key]
	}

	func addObject(_ object: T, forKey key: String) {
	objects[key] = object
	}

JohnSundell / WrappingSingletons.swift

Last active October 26, 2017 18:23

This is a great technique if you need to interact with singleton-based APIs but still have great testability

	import UIKit

	// Create a protocol that defines what APIs that you need from the singleton
	protocol Application {
	func open(url: URL)
	}

	// Make the singleton-based class conform to your protocol
	extension UIApplication: Application {
	func open(url: URL) {

JohnSundell / Perform.swift

Last active December 21, 2019 14:43

A function that enables you to easily wrap throwing APIs, to provide a custom error

	/**
	* Perform a throwing expression, and throw a custom error in case the expression threw
	*
	* - parameter expression: The expression to execute
	* - parameter error: The custom error to throw instead of the expression's error
	* - throws: The given error
	* - returns: The return value of the given expression
	*/
	func perform<T>(_ expression: @autoclosure () throws -> T, orThrow errorExpression: @autoclosure () -> Error) throws -> T {
	do {

JohnSundell / AssertThrowsError.swift

Created February 19, 2017 13:36

A function that asserts that an expression throws a given error

	/**
	* Copyright (c) John Sundell 2017
	* Licensed under the MIT license
	*/

	import Foundation
	import XCTest

	/**
	* Assert that an expression throws a given error

JohnSundell / OnboardingManager.swift

Last active May 21, 2020 08:19

An example of using #function for user defaults properties, and a test that guards against property name changes

	import UIKit

	class OnboardingManager {
	private let userDefaults: UserDefaults

	init(userDefaults: UserDefaults = .standard) {
	self.userDefaults = userDefaults
	}

	func presentOnboardingControllerIfNeeded(in viewController: UIViewController) {

JohnSundell / Providing-a-unified-Swift-error-API-0.swift

Last active March 27, 2017 16:39

	func loadSearchData(matching query: String) throws -> Data {
	let urlString = "https://my.api.com/search?q=\(query)"

	guard let url = URL(string: urlString) else {
	throw SearchError.invalidQuery(query)
	}

	return try Data(contentsOf: url)
	}

JohnSundell / Providing-a-unified-Swift-error-API-1.swift

Created March 27, 2017 16:41

	func loadSearchData(matching query: String) throws -> Data {
	let urlString = "https://my.api.com/search?q=\(query)"

	guard let url = URL(string: urlString) else {
	throw SearchError.invalidQuery(query)
	}

	do {
	return try Data(contentsOf: url)
	} catch {

JohnSundell / Providing-a-unified-Swift-error-API-2.swift

Created March 27, 2017 16:42

	func perform<T>(_ expression: @autoclosure () throws -> T,
	orThrow error: Error) throws -> T {
	do {
	return try expression()
	} catch {
	throw error
	}
	}

JohnSundell / Providing-a-unified-Swift-error-API-3.swift

Created March 27, 2017 16:44

	func loadSearchData(matching query: String) throws -> Data {
	let urlString = "https://my.api.com/search?q=\(query)"

	guard let url = URL(string: urlString) else {
	throw SearchError.invalidQuery(query)
	}

	return try perform(Data(contentsOf: url),
	orThrow: SearchError.dataLoadingFailed(url))
	}