Andee Liao andeeliao

Interview Questions for iOS Developers

1. Classes vs structs

In Swift, structs are value types whereas classes are reference types. When you copy a struct, you end up with two unique copies of the data. When you copy a class, you end up with two references to one instance of the data. It’s a crucial difference, and it affects your choice between classes or structs. (+ Class extendable, struct does not.)

2. What’s the difference between `var` and `let`? Which one would you choose for properties in a struct and why?

Both let and var are for creating variables in Swift. let helps you create immutable variables (constants) while on the other hand var creates mutable variables.

3. What does the mutating keyword mean?

The mutating keyword lets callers know that the method is going to make the value change.

	{
	"categories": [
	{
	"category_id": "10000000",
	"group": "special",
	"hierarchy": [
	"Bank Fees"
	]
	},
	{

	func +(lhs: NSAttributedString, rhs: NSAttributedString) -> NSAttributedString {

	let a = lhs.mutableCopy() as! NSMutableAttributedString
	let b = rhs.mutableCopy() as! NSMutableAttributedString

	a.appendAttributedString(b)

	return a.copy() as! NSAttributedString
	}

	var amqp = require('amqplib/callback_api');

	// if the connection is closed or fails to be established at all, we will reconnect
	var amqpConn = null;
	function start() {
	amqp.connect(process.env.CLOUDAMQP_URL + "?heartbeat=60", function(err, conn) {
	if (err) {
	console.error("[AMQP]", err.message);
	return setTimeout(start, 1000);
	}

	extension UIViewController {
	func topMostViewController() -> UIViewController {
	if self.presentedViewController == nil {
	return self
	}
	if let navigation = self.presentedViewController as? UINavigationController {
	return navigation.visibleViewController.topMostViewController()
	}
	if let tab = self.presentedViewController as? UITabBarController {
	if let selectedTab = tab.selectedViewController {

Andee Liao andeeliao

Interview Questions for iOS Developers

1. Classes vs structs

2. What’s the difference between var and let? Which one would you choose for properties in a struct and why?

3. What does the mutating keyword mean?

2. What’s the difference between `var` and `let`? Which one would you choose for properties in a struct and why?