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Objective-C to Swift conversion cheat sheet

Here is the Rosetta Stone for Objective-C to Swift

Paul Hudson       @twostraws

If you're moving from Objective-C to Swift, or perhaps from Swift to Objective-C, it can be useful to have a quick start guide showing equivalent code samples in both languages. Well, that's exactly what you'll find below: a Rosetta stone of Apple development, demonstrating variables, collections, functions, classes, and more.

In all instances, Objective-C code is shown on the left and the equivalent Swift code on the right. Where necessary I have added small clarification notes to give you more understanding.

If you can already program in Swift and want to get up to speed with Objective-C as quickly as possible, I have just the book for you: Objective-C for Swift Developers.

Variables and constants

Create a variable
NSInteger score = 556;
NSString *name = @"Taylor";
BOOL loggedIn = NO;
var score = 556
var name = "Taylor"
var loggedIn = false
Create a constant
const NSInteger score = 556;
NSString * const name = @"Taylor";
const BOOL firstRun = YES;

Constants are used infrequently in Objective-C.

let score = 556
let name = "Taylor"
let firstRun = true

Constants are extremely common in Swift.

Create a variable array
NSMutableArray *items = [NSMutableArray new];
NSMutableArray<NSString *> *results = [NSMutableArray new];

Generics in Objective-C are a contentious issue; you will see both styles.

var items = [String]()
var results = Array<String>()

The first style is strongly preferred.

Create a constant array
NSArray *grades = @[@90, @85, @97];
NSArray *names = @[@"Taylor", @"Adele", @"Justin"];
let grades = [90, 85, 97]
let names = ["Taylor", "Adele", "Justin"]
Adding a value type to an array
NSMutableArray *array = [NSMutableArray new];
[array addObject:[NSValue valueWithRect:CGRectMake(0, 0, 32, 64)]];

Value types must be wrapped in a reference type before being added to a collection.

var array = [CGRect]()
array.append(CGRect(x: 0, y: 0, width: 32, height: 64))
Create a dictionary
NSDictionary *houseNumbers = @{ @"Paul": @7, @"Jess": @56, @"Peter": @332 };
let houseNumbers = ["Paul": 7, "Jess": 56, "Peter": 332]
Define an enum
typedef NS_ENUM(NSInteger, ShapeType) {
enum ShapeType: Int {
    case circle
    case rectangle
    case hexagon
Appending a string
NSString *first = @"Hello, ";
NSString *second = [first stringByAppendingString:@" world!"];
let first = "Hello, "
let second = first + "world!"
Adding to a number
NSInteger rating = 4;
rating += 3;
var rating = 4
rating += 1
rating += 3
String interpolation
NSString *account = @"twostraws";
NSString *str = [NSString stringWithFormat:@"Follow me on Twitter: %@", account];
let account = "twostraws"
let str = "Follow me on Twitter: \(account)"
Printing debug information
NSString *username = @"twostraws";
NSLog(@"Username is %@", username);
let username = "twostraws"
print("Username is \(username)")

Control flow

Checking a condition
NSInteger result = 86;

if (result >= 85) {
    NSLog(@"You passed the test!");
} else {
    NSLog(@"Please try again.");
let result = 86

if result >= 85 {
    print("You passed the test!")
} else {
    print("Please try again.")
Looping a set number of times
for (NSInteger i = 0; i < 100; ++i) {
    NSLog(@"This will be printed 100 times.");
for _ in 0 ..< 100 {
    print("This will be printed 100 times.")
Looping over an array
NSArray *companies = @[@"Apple", @"Facebook", @"Twitter"];

for (NSString *name in companies) {
    NSLog(@"%@ is a well-known tech company.", name);
let companies = ["Apple", "Facebook", "Twitter"]

for name in companies {
    print("\(name) is a well-known tech company.")
Switching over a value
NSInteger rating = 8;

switch (rating) {
    case 0 ... 3:
    case 4 ... 7:
    case 8 ... 10:
        NSLog(@"Invalid rating.");

Many people are unaware that Objective-C has range support, so you might see alternative syntax.

let rating = 8

switch rating {
case 0...3:
case 4...7:
case 8...10:
    print("Invalid rating.")

Swift will not fall through cases unless you use the fallthrough keyword.


A function that accepts no parameters and returns nothing
- (void)printGreeting {

[self printGreeting];
func printGreeting() {

A function that accepts no parameters and returns a string
- (NSString*)printGreeting {
    return @"Hello!";

NSString *result = [self printGreeting];
func printGreeting() -> String {
    return "Hello!"

let result = printGreeting()
A function that accepts a string and returns a string
- (NSString*)printGreetingFor:(NSString*)user {
    return [NSString stringWithFormat:@"Hello, %@!", user];

NSString *result = [self printGreetingFor:@"Paul"];

The name for the first parameter should be part of the method name itself.

func printGreeting(for user: String) -> String {
    return "Hello, \(user)!"

let result = printGreeting(for: "Paul")
A function that accepts a string and an integer, and returns a string
- (NSString*)printGreetingFor:(NSString*)user withAge:(NSInteger)age {
    if (age >= 18) {
        return [NSString stringWithFormat:@"Hello, %@! You're an adult.", user];
    } else {
        return [NSString stringWithFormat:@"Hello, %@! You're a child.", user];

NSString *result = [self printGreetingFor:@"Paul" withAge:38];
func printGreeting(for user: String, age: Int) -> String {
    if age >= 18 {
        return "Hello, \(user) You're an adult."
    } else {
        return "Hello, \(user)! You're a child."

let result = printGreeting(for: "Paul", age: 38)
Returning multiple values from a function
- (NSDictionary<NSString*, NSString*>*)loadAddress {
    return @{
        @"house": @"65, Park Street",
        @"city": @"Bristol",
        @"country": @"UK"

NSDictionary<NSString*, NSString*> *address = [self loadAddress];
NSString *house = address[@"house"];
NSString *city = address[@"city"];
NSString *country = address[@"country"];

Objective-C does not support tuples, so dictionaries or arrays are used instead.

func loadAddress() -> (house: String, city: String, country: String) {
    return ("65, Park Street", "Bristol", "UK")

let (city, street, country) = loadAddress()
A closure that accepts no parameters and returns nothing.
void (^printUniversalGreeting)(void) = ^{
    NSLog(@"Bah-weep-graaaaagnah wheep nini bong");

let universalGreeting = {
    print("Bah-weep-graaaaagnah wheep nini bong")

A closure that accepts no parameters and returns a string.
NSString* (^getUniversalGreeting)(void) = ^{
    return @"Bah-weep-graaaaagnah wheep nini bong";

NSString *greeting = getUniversalGreeting();
NSLog(@"%@", greeting);
let getUniversalGreeting = {
    return "Bah-weep-graaaaagnah wheep nini bong"

let greeting = getUniversalGreeting()
A closure that accepts a string parameter and returns a string.
NSString* (^getGreeting)(NSString *) = ^(NSString *name) {
    return [NSString stringWithFormat:@"Live long and prosper, %@.", name];

NSString *greeting = getGreeting(@"Paul");
NSLog(@"%@", greeting);
let getGreeting = { (name: String) in
    return "Live long and prosper, \(name)."

let greeting = getGreeting("Paul")


Creating an empty class
@interface MyClass : NSObject

@implementation MyClass
class MyClass: NSObject {

It's preferable to use structs rather than classes. You may not need to inherit from NSObject.

Creating a class with two properties
@interface User : NSObject
@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSInteger age;

@implementation User

class User {
    var name: String
    var age: Int

    init(name: String, age: Int) { = name
        self.age = age

Swift requires you to create an initializer to give these properties default values.

Creating a class with a private property
// in the header file
@interface User : NSObject
@property (nonatomic, copy) NSString *name;

// in the implementation file
@interface User()
@property (nonatomic, assign) NSInteger age;

@implementation User


Objective-C doesn't really support private properties, so this workaround is common.

class User {
    var name: String
    private var age: Int

    init(name: String, age: Int) { = name
        self.age = age
Creating a class with an instance method
@interface Civilization : NSObject
- (NSInteger)getMeaningOfLife;

@implementation Civilization
- (NSInteger)getMeaningOfLife {
    return 42;
class Civilization {
    func getMeaningOfLife() -> Int {
        return 42
Creating a class with a static method
@interface Civilization : NSObject
+ (NSInteger)getMeaningOfLife;

@implementation Civilization
+ (NSInteger)getMeaningOfLife {
    return 42;

The difference is small: + is used rather than -.

class Civilization {
    class func getMeaningOfLife() -> Int {
        return 42

Swift also supports static methods – methods that may not be overridden in a subclass.

Extending a type with a new method
@interface NSString (Trimming)
- (NSString*)trimmed;

@implementation NSString (Trimming)

- (NSString*)trimmed {
    return [self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

extension String {
    func trimmed() -> String {
        return trimmingCharacters(in: .whitespacesAndNewlines)
Checking the class of an object
if ([object isKindOfClass:[YourClass class]]) {
    NSLog(@"This is a YourClass.");
if object is YourClass {
    print("This is a YourClass.")
Dog *poodle = (Dog*)animalObject;
let poodle = animalObject as? Dog
let poodle = animalObject as! Dog

The former will set poodle to nil if it is not a dog; the latter will crash your program if it is not a dog.


Running code on different threads
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSLog(@"Running in the background...");
    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"Running back on the main thread");
}); {
    print("Running in the background...")
    DispatchQueue.main.async {
        print("Running on the main thread")


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