Swift 5 Cheatsheet

A cheatsheet for Swift 5. Including examples of common Swift code and short explanations of what it does and how it works. Perfect for beginner iOS developers!

How to Use

The cheatsheet is in Markdown format. Simply read the cheatsheet online, or download the repository and open it. Use your favorite Markdown editor to export to PDF or HTML.

Although we'd love for you to print it out and hang it on your desk, please think about the environment.

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Distributed under the MIT license. See LICENSE for more information.

Variables

Use var for variables that can change ("mutable") and let for constants that can't change ("non-mutable").

Integers are "whole" numbers, i.e. numbers without a fractional component.

var meaningOfLife: Int = 42

Floats are decimal-point numbers, i.e. numbers with a fractional component.

var phi: Float = 1.618

Doubles are floating point numbers with double precision, i.e. numbers with a fractional component. Doubles are preferred over floats.

let pi: Double = 3.14159265359

A String is a sequence of characters, like text.

var message: String = "Hello World!"

A boolean can be either true or false. You use booleans for logical operations.

var isLoggedIn: Bool = false

You can assign the result of an expression to a variable, like this:

var result: Int = 1 + 2

An expression is programmer lingo for putting stuff like variables, operators, constants, functions, etc. together. Like a + b in this example:

let a = 3
let b = 4
let c = a + b

Swift can determine the type (Int, Double, String, etc.) of a variable on its own. This is called type inference. In this example, the type of name is inferred to be String.

var name = "Arthur Dent"

Variables can be optional, which means it either contains a value or it's nil. Optionals make coding Swift safer and more productive. Here's an optional string:

var optionalMessage: String?

Functions

Functions are containers of Swift code. They have input and output. You often use functions to create abstractions in your code, and to make your code reusable.

Here's an example of a function:

func greetUser(name: String, bySaying greeting:String = "Hello") -> String
{
    return "\(greeting), \(name)"
}

This function has two parameters called name and greeting, both of type String. The second parameter greeting has an argument label bySaying. The return type of the function is String, and its code is written between those squiggly brackets.

You call the function like the following. The function is called, with two arguments, and the return value of the function is assigned to message.

let message = greetUser(name: "Zaphod", bySaying: "Good Morning")

Courses, books, documentation, etc. uses a special notation for function signatures. It'll use the function name and argument labels, like greetUser(name:bySaying:), to describe the function.

Operators

The assignment operator = assigns what's right of the operator to what's left of the operator. Don't confuse it with ==!

let age = 42

Swift has a few basic math operators:

a + b for addition (works for strings too)
a - b for subtraction
a * b for multiplication
a / b for division
a % b for remainder (or use isMultiple(of:))
-a for minus (invert sign)

Unlike other programming languages, Swift does not have -- and ++ operators. Instead it has:

a += b for addition, such as n += 1 for n++ or n = n + 1
a -= b for subtraction, such as n -= 1 for n-- or n = n - 1

You can also use += for arrays:

var rappers = ["Eminem", "Jay-Z", "Snoop Dogg"]
rappers += ["Tupac"]

Swift has 6 comparison operators:

a == b for equality, i.e. "a is equal to b"
a != b for inequality, i.e. "a is not equal to b"
a > b for greater than, i.e. "a is greater than b"
a < b for less than, i.e. "a is less than b"
a >= b for greater than or equal
a <= b for less than or equal

Swift also has the identity operators === and !==. You can use them to test if two variables reference the exact same object. Contrast this with == and !=, which merely test if two objects are equal to each other.

You can also compare strings, which is helpful for sorting. Like this:

"abc" > "xyz"         // false
"Starbucks" > "Costa" // true
"Alice" < "Bob"       // true

Swift has 3 logical operators:

a && b for Logical AND, returns true if a and b are true, or false otherwise
a || b for Logical OR, returns true if either a or b is true, or both are true, or false otherwise
!a for Logical NOT, returns true if a is false, and false if a is true (i.e., the opposite of a)

Swift has a few range operators. You can use them to define ranges of numbers and strings.

a...b, the closed range operator, defines a range from a to b including b
a..<b, the half-open range operator, defines a range from a to b not including b

You can also use one-sided ranges. They're especially useful in arrays.

a... in array[a...] defines a range from a to the end of the array
...a in array[...a] defines a range from the beginning of the array to a
..<a in array[..<a] defines a range from the beginning of the array to a, not including a itself

Classes, Objects, Properties

Classes are basic building blocks for apps. They can contain functions, sometimes called methods, and variables, called properties.

class Office: Building, Constructable
{
    var address: String = "1 Infinite Loop"
    var phone: String?

    @IBOutlet weak var submitButton:UIButton?

    lazy var articles:String = {
        return Database.getArticles()
    }()

    override init()
    {
        address = "1 Probability Drive"
    }

    func startWorking(_ time:String, withWorkers workers:Int)
    {
        print("Starting working at time \(time) with workers \(workers)")
    }
}

The class definition starts with class, then the class name Office, then the Building class it inherits from, and then the Constructable protocol it conforms to. Inheritance, protocols, all that stuff, is part of Object-Oriented Programming.

Properties are variables that belong to a class instance. This class has 4 of them: address, phone, the outlet submitButton and the lazy computed property articles. Properties can have a number of attributes, like weak and @IBOutlet.

The function init() is overridden from the superclass Building. The class Office is a subclass of Building, so it inherits all functions and properties that Building has.

You can create an instance of a class, and change its properties, like this:

let buildingA = Office()
buildingA.address = "Sector ZZ9 Plural Z Alpha"

Extensions let you add new functions to existing types. This is useful in scenarios where you can't change the code of a class. Like this:

extension Building
{
    func evacuate() {
        print("Please leave the building in an orderly fashion.")
    }
}

Structs

Structs or structures in Swift allow you to encapsulate related properties and functionality in your code, that you can reuse. Structs are value types.

We declare them like this:

struct Jedi {
    var name: String
    var midichlorians: Int
}

You can create an instance of the Jedi struct like this:

var obi_wan = Jedi(name: "Obi-Wan Kenobi", midichlorians: 13400)

Here's how you can read a property from obi_wan:

print(obi_wan.midichlorians)
// Output: 13400

We can also include functions inside our structs, like this:

struct Jedi {
    var name: String
    var midichlorians: Int

    func mindTrick() {
        print("These aren't the Droids you're looking for...")
    }
}

// Instance of a struct
var obi_wan = Jedi(name: "Obi-Wan Kenobi", midichlorians: 13400)

// Reading a property
print(obi_wan.midichlorians) 

// Calling mindTrick() function
obi_wan.mindTrick()

Protocols

Protocols define a "contract"; a set of functions and properties that a type, like a class, must implement if it wants to conform to the protocol.

Protocols are declared like this:

protocol Healer {
    func heal()
}

In this example Imperial troops are fine on their own, but can conform to the Healer protocol and support their fellow troopers in combat:

protocol Healer {
    func heal()
}

struct TiePilot {
    var starfigherModel: String = "TIE/IN Interceptor"
    var rank: String = "Lieutenant"
}

struct StormTrooper: Healer {
    var name: String = "TK-9091"
    var unit: String = "501st Legion"
    
    func heal() {
        print("Deploying Advanced Medical Probe!")
    }
}

You can also use protocols as types. Like this:

struct Squadron 
{
    var leader: EliteStormTrooper
    var troopers: [StormTrooper]
    var healer: Healer

    func init(...) { ... }
}

var squad5 = Squadron(...)
squad5.healer = StormTrooper(...)

In the above code, you can assign an object of type StormTrooper to the healer property of type Healer, because the StormTrooper type conforms to the Healer protocol. You can assign anything to it, as long as it conforms to the right protocol.

Control Flow

Conditionals

This is an if-statement, or conditional. You use them to make decisions based on logic.

if isActive
{
    print("This user is ACTIVE!")
} else {
    print("Inactive user...")
}

You can combine multiple conditionals with the if-elseif-else syntax, like this:

var user:String = "Bob"

if user == "Alice" && isActive
{
    print("Alice is active!")
}
else if user == "Bob" && !isActive
{
    print("Bob is lazy!")
}
else
{
    print("When none of the above are true...")
}

The && is the Logical AND operator. You use it to create logical expressions that can be evaluated to true or false. Like this:

if user == "Deep Thought" || meaningOfLife == 42
{
    print("The user is Deep Thought, or the meaning of life is 42...")
}

Operators, like &&, have an order of precedence. This determines which operator has priority over another; which operator is evaluated before the other. Check this out:

let a = 2 + 3 * 4
// Output: 14

The value of a is 14 and not 20, because multiplication precedes addition. A quick overview: ! * / + - && ||.

You can change the order of operations with parentheses. Like this:

let a = (2 + 3) * 4
// Output: 20

This groups the addition, which is now evaluated before the multiplication. Precedence rules are especially important when working with the logical && (AND) and || (OR) operators. && goes before ||. Check this out:

let isPresident = true
let threatLevel = 1
let officerRank = 1

if threatLevel > 5 && officerRank >= 3 || isPresident {
    print("(1) FIRE ROCKETS!!!")
}

if threatLevel > 5 && (officerRank >= 3 || isPresident) {
    print("(2) FIRE ROCKETS!!!")
}
// Output: (1) FIRE ROCKETS!!!

Notice how the result of the above conditionals changes based on the parentheses, while their operators and operands stay the same.

In the first conditional, the rockets are fired because isPresident is true and the entire conditional evaluates to (false && false -> false) || true -> false || true -> true.
In the second conditional, the rockets aren't fired even though isPresident is true. The entire conditional evaluates to false && (false || true -> true) -> false && true -> false.

Swift has a special operator, called the ternary conditional operator. It's coded as a ? b : c. If a is true, the expression returns b, and if a is false, the expression returns c. It's the equivalent of this:

if a {
    b
} else {
    c
}

Loops

Loops repeat stuff. It's that easy. Like this:

for i in 1...5 {
    print(i)
}
// Output: 1 2 3 4 5

This prints 1 to 5, including 5! You can also use the half-open range operator a..<b to loop from a to b not including b. Like this:

for i in 1..<5 {
    print(i)
}
// Output: 1 2 3 4

You can use continue in a loop to skip to the next iteration, and break to quit looping altogether. Like this:

for i in 0..<10 
{
    if i.isMultiple(of: 2) {
        continue
    }

    if i == 7 {
        break
    }

    print(i)
}
// Output: 1 3 5

When you don't know how many times a loop needs to run exactly, you can use a while loop. A while loop keeps iterating as long as its expression is true.

var steps = 42

while steps > 0 {
    steps -= 9
    print(steps)
}
// Output: 33 24 15 6 -3

A while loop will evaluate its condition at the top of the loop, so before the next iteration runs. The repeat-while evaluates its condition at the end of the loop. It'll always run the first iteration, before evaluating the loop condition.

Switch

A switch statement takes a value and compares it against one of several cases. It's similar to the if-else if-else conditional, and it's an elegant way of dealing with multiple states.

An example:

enum WeatherType {
    case rain, clear, sunny, overcast, tsunami, earthquake, snow;
}

let weather = WeatherType.sunny

switch weather 
{
    case .rain:
        print("Bring a raincoat!")
    case .clear, .sunny:
        print("Don't forget your sunglasses.")
    case .overcast:
        print("It's really depressing.")
    case .tsunami, .earthquake:
        print("OH NO! BIG WAVE!")
    default:
        print("Expect the best, prepare for the worst.")
}

In Swift, switch statements don't have an implicit fall-through, but you can use fallthrough explicitly. Every case needs to have at least one line of code in it. You don't have to use a break explicitly to end a case.

The switch cases need to be exhaustive. For example, when working with an enum, you'll need to incorporate every value in the enumeration. You can also provide a default case, which is similar to else in a conditional.

You can also use Swift ranges to match interval for numbers, use tuples to match partial values, and use Swift's where keyword to check for additional conditions.

Strings

Strings are pretty cool. Here's an example:

var jobTitle: String = "iOS App Developer"

Inside a string, you can use string interpolation to string together multiple strings. Like this:

var hello = "Hello, \(jobTitle)"
// Output: Hello, iOS App Developer

You can also use the + addition operator to concatenate multiple strings:

let a  = "Never gonna"
let b  = "give you up"
let rr = a + " " + b

You can also turn an Int into a String:

let number = 42
let numberAsString = "\(number)"

And vice-versa:

let number = "42"
let numberAsInt = Int(number)

You can loop over the characters of a string like this:

let text = "Forty-two!"

for char in text {
    print(char)
}

You can get individual characters and character ranges by using indices, like this:

let text = "Forty-two!"
text[text.startIndex] // F
text[text.index(before: text.endIndex)] // !
text[text.index(text.startIndex, offsetBy: 3)] // t
text[..<text.index(text.startIndex, offsetBy: 3)] // For
text[text.index(text.endIndex, offsetBy: -4)...] // two!

You can trim all whitespace at the start and end of a string like this:

let text = "  Forty-two!  "
let trimmed = text.trimmingCharacters(in: .whitespacesAndNewlines) // Forty-two!

Optionals

Optionals can either be nil or contain a value. You must always unwrap an optional before you can use it.

This is Bill. Bill is an optional.

var bill: String? = nil

You can unwrap bill in a number of ways. First, this is optional binding.

if let definiteBill = bill {
    print(definiteBill)
}

In this example, you bind the non-optional value from bill to definiteBill but only when bill is not nil. It's like asking: "Is it not nil?" OK, if not, then assign it to this constant and execute that stuff between the squiggly brackets.

You can also use force-unwrapping to unwrap an optional. Like this:

var droid: String? = "R2D2"

if droid != nil {
    print("This is not the droid you're looking for: \(droid!)")
}

See how that droid is force-unwrapped with the exclamation mark !? You should keep in mind that if droid is nil when you force-unwrap it, your app will crash.

You can also use optional chaining to work your way through a number of optionals. This saves you from coding too much optional binding blocks. Like this:

view?.button?.title = "BOOYAH!"

In this code, view, button and title are all optionals. When view is nil, the code "stops" before button, so the button property is never accessed.

One last thing... the nil-coalescing operator. You can use it to provide a default value when an expression results in nil. Like this:

var meaningOfLife = deepThought.think() ?? 42

See that ??. When deepThought.think() returns nil, the variable meaningOfLife is 42. When that function returns a value, it's assigned to meaningOfLife.

Collections

Arrays

Arrays are a collection type. Think of it as a variable that can hold multiple values, like a closet that can contain multiple drawers. Arrays always have numerical index values. Arrays always contain elements of the same type.

var hitchhikers = ["Ford", "Arthur", "Zaphod", "Trillian"]

You can add items to the array:

hitchhikers += ["Marvin"]

You can get items from the array with subscript syntax:

let arthur = hitchhikers[1]

Remember that arrays are zero-index, so the index number of the first element is 0 (and not 1).

You can iterate arrays, like this:

for name in hitchhikers {
    print(name)
}

A helpful function on arrays is enumerated(). It lets you iterate index-value pairs, like this:

for (index, name) in hitchhikers.enumerated() {
    print("\(index) = \(name)")
}

Dictionaries

Dictionaries are also collection types. The items in a dictionary consists of key-value pairs. Unlike arrays, you can set your own key type. Like this:

var score = [
    "Fry": 10,
    "Leela": 29,
    "Bender": 1,
    "Zoidberg": 0
]

What's the type of this dictionary? It's [String: Int]. Just like with arrays, you can use subscript syntax to get the value for a key:

print(score["Leela"])
// Output: 29

You can add a key-value pair to a dictionary like this:

score["Amy"] = 9001

Change it like this:

score["Bender"] = -1

And remove it like this:

score.removeValue(forKey: "Zoidberg")

You can also iterate a dictionary, like this:

for (name, points) in score
{
    print("\(name) has \(points) points");
}

Sets

Sets in Swift are similar to arrays and dictionaries. Just like arrays and dictionaries, the Set type is used to store multiple items of the same type in one collection.

Here's an example:

var fruit:Set = ["apple", "banana", "strawberry", "jackfruit"]

You can add and remove items like this:

fruit.insert("pineapple")
fruit.remove("banana")

Sets are different from arrays and dictionaries, in these ways:

Sets don't have an order – they're literally unsorted
Every item in a set needs to be unique
Sets don't have indices or keys
Instead, a set's values need to be hashable
Because set items are hashable, you can search sets in O(1) time

Here's how you can quickly search a set:

let movies:Set = ["Rocky", "The Matrix", "Lord of the Rings"]

if movies.contains("Rocky") {
    print("Rocky is one of your favorite movies!")
}

Sets are particularly useful for membership operations, to find out if sets have items in common for example. We can make a union of sets, subtract sets, intersect them, and find their differences.

Consider the following Italian coffees and their ingredients:

let cappuccino:Set = ["espresso", "milk", "milk foam"]
let americano:Set  = ["espresso", "water"]
let machiato:Set   = ["espresso", "milk foam"]
let latte:Set      = ["espresso", "milk"]

Can we find the union (add items) of two coffees?

machiato.union(latte)
// ["espresso", "milk foam", "milk"]

Can we subtract one coffee from another?

cappuccino.subtracting(americano)
// ["milk foam", "milk"]

Can we find the intersection (shared items) of two coffees?

latte.intersection(cappuccino)
// ["espresso", "milk"]

Can we find the difference between two coffees?

latte.symmetricDifference(americano)
// ["milk", "water"]

Closures

With closures you can pass around blocks of code, like functions, as if they are variables. You use them, for example, by passing a callback to a lengthy task. When the task ends, the callback – a closure – is executed.

You define a closure like this:

let authenticate = { (name: String, userLevel: Int) -> Bool in
    return (name == "Bob" || name == "Alice") && userLevel > 3
}

You call the closure like this:

authenticate("Bob", 7)

Closures have a type, that reflect the closure's parameters and its return type. The type of the closure for authenticate is (String, Int) -> Bool.

If we had a user interface for authenticating a user, then we could pass the closure as a callback like this:

let loginVC = MyLoginViewController(withAuthCallback: authenticate)

You always write a closure inside squiggly brackets { }. Within the closure, you can declare zero, one or more parameters (with types), and optionally, a return type, followed by in.

Closure syntax is flexible, and has a few shorthands, which means you can leave out parts of the closure's declaration to make the code more concise.

For example, the closure in this code:

let names = ["Zaphod", "Trillian", "Ford", "Arthur", "Marvin"]
let sortedNames = names.sorted(by: <)

... is the same as this code:

names.sorted(by: { (s1: String, s2: String) -> Bool in
    return s1 < s2
})

... and that's the same as this, too:

names.sorted(by: { s1, s2 in s1 < s2 } )

... and even this, too:

names.sorted { $0 < $1 }

Another use case for closures is multi-threading with Grand Central Dispatch. Like this:

DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + .seconds(60)) {  
    // Dodge this!  
}

In the above example, the last argument of asyncAfter(deadline:execute:) is a closure. It uses the trailing closure syntax. When a closure is the last argument of a function call, you can write it after the function call parentheses and omit the argument label.

Guard and Defer

Guard

The guard statement helps you to return functions early. It's a conditional, and when it isn't met you need to exit the function with return.

Like this:

func loadTweets(forUserID userID: Int) 
{
    guard userID > 0 else {
        return
    }

    // Load the tweets...
}

You can read that as: "Guard that the User ID is greater than zero, or else, exit this function". Guard is especially powerful when you have multiple conditions that should return the function.

Guard blocks always need to exit its enclosing scope, i.e. transfer control outside of the scope, by using return, throw, break or continue.

You can also combine guard and if let (optional binding) into guard let. This checks if the given expression is not nil, and assigns it to a constant. When the expression is nil, the else clause of guard is executed.

guard let user = object?.user else {
    return
}

You can now use the user constant in the rest of the scope, below the guard let block.

Defer

With defer you can define a code block that's executed when your function returns. The defer statement is similar to guard, because it also helps with the flow of your code.

Like this:

func saveFile(withData data: Data) {

    let filePointer = openFile("../example.txt")

    defer {
        closeFile(filePointer)
    }

    if filePointer.size > 0 {
        return
    }

    if data.size > 512 {
        return
    }

    writeFile(filePointer, withData: data)
}

In the example code you're opening a file and writing some data to it. As a rule, you need to close the file pointer before exiting the function.

The file isn't written to when two conditions aren't met. You have to close the file at those points. Without the defer statement, you would have written closeFile(_:) twice.

Thanks to defer, the file is always closed when the function returns.

Generics

In Swift your variables are strong typed. When you set the type of animals your farm can contain to Duck, you can't change that later on. With generics however, you can!

Like this:

func insertAnimal<T>(_ animal: T, inFarm farm: Farm) 
{
    // Insert `animal` in `farm`
}

This is a generic function. It uses a placeholder type called T instead of an actual type name, like String.

If you want to insert ducks, cows, birds and chickens in your farm, you can now do that with one function instead of 4.

Tuples

With tuples you get two (or more) variables for one. They help you structure your code better. Like this:

let coffee = ("Cappuccino", 3.99)

You can now get the price of the coffee like this:

let (name, price) = coffee
print(price)
// Output: 3.99

When you need just the name, you can do this:

let (name, _) = coffee
print(name)
// Output: Cappuccino

You can also name the elements of a tuple, like this:

let flight = (code: "XJ601", heading: "North", passengers: 216)
print(flight.heading) 
// Output: North

Enumerations

With enumerations, also known as enums, you can organize groups of values that are related. Here's an example:

enum Compass {
    case north
    case east
    case south
    case west
}

Here's how you use them:

let direction: Compass = .south

Enums and the switch statement are a powerful couple. Here's an example:

enum Emotion {
    case happy, sad, angry, scared, surprised
}

switch robot.mood {
case .angry:
    robot.destroyAllHumans()
case .sad:
    robot.cry()
case .happy:
    robot.play("happy.mp3")
case default:
    print("Error: emotion not supported.")
}

You can also assign raw values to enums, by using existing Swift types like String. Here's an example:

enum Flavor:String {
    case vanilla = "vanilla"
    case strawberry = "strawberry"
    case chocolate = "chocolate"
}

With this approach, you can get the string value for an enum like this:

let icecream = Flavor.vanilla
print(icecream.rawValue)
// Output: vanilla

You can now also use a string to create an enum, like this:

let icecream = Flavor(rawValue: "vanilla")
print(icecream)
// Output: Optional(Flavor.vanilla)

You can also associate values with individual cases of an enumeration, like this:

enum Item {
    case weapon(Int, Int)
    case food(Int)
    case armor(Int, Int, Double)
}

You can now use the enumeration's associated values, like this:

func use(item: Item)
{
    switch item {
    case .weapon(let hitPoints, _):
        player.attack(hitPoints)
    case .food(let health):
        player.health += health
    case .armor(let damageThreshold, let weight, let condition):
        player.damageThreshold = Double(damageThreshold) * condition
    }
}

In the above code, we're using hitPoints to "attack" in case item is the enum type weapon(Int, Int). This way you can associate additional values with an enum case.

Error Handling

Errors in Swift can be thrown, and should be caught. You can define an error type like this:

enum CreditCardError: Error {
    case insufficientFunds
    case issuerDeclined
    case invalidCVC
}

When you code a function that can throw errors, you have to mark its function definition with throws. Like this:

func processPayment(creditcard: String) throws {
    ...

Inside the function, you can then throw an error like this:

throw CreditCardError.insufficientFunds

When you use a function that can throw errors, you have to wrap it in a do-try-catch block. Like this:

do {
    try processPayment(creditcard: "1234.1234")
}
catch {
    print(error)
}

In the example above, the processPayment(creditcard:) function is marked with the try keyword. When an error occurs, the catch block is executed.

Commenting

There are 3 types of comments:

1. Documentary: Describes the history and development of the file. Their core purpose is to improve code maintainability. Most notable examples are:

Filename
Project name
Creation and modification dates
Author
Copyright
Version
History of changes
Dependencies

Documentary comments are wordy and error-prone if typed manually. Capture only those details, which are not available to version controls tools like git.

We are dealing with documentary comments every day, often without realizing it:

//
//  AppDelegate.swift
//
//  Created by John Doe on 28/7/20.
//  Copyright © 2020 Acme Inc. All rights reserved.
//

2. Functional: Adds information and special directives to the development process. Most notable examples in Swift are:

Diagnostic directives: #warning, #error
Annotations: TODO, MARK, FIXME, and 3rd-party-specific like swiftlint:disable
Notes about who fixed what bug when, e.g. "Bugfix: This is how I fixed it. -VABU"
Performance improvement notes

3. Explanatory: Summarizes code or explains the programmer's intent. Explanatory comments must answer the question why instead of what.

Explanatory comments make the most sense in these scenarios:

Code does not fit project conventions
Algorithm description: name, complexity, documentation
Complex regular expressions
Workarounds and hacks

Comment Syntax

Swift comments can be written in two formats:

Each line is preceded by a double slash //

// <#Description#>
//
// - Parameter value: <#value description#>
// - Returns: <#return value description#>
func isOdd(_ value: Int) -> Bool {
    return abs(value) % 2 == 1
}

Javadoc-style block comments /* … */

/* <#Description#>

  - Parameter value: <#value description#>
  - Returns: <#return value description#>
*/
func isOdd(_ value: Int) -> Bool {
    return abs(value) % 2 == 1
}

Resources

No cheatsheet is complete without a list of resources with more information. Wanna see how deep the rabbit hole really goes?

Name		Name	Last commit message	Last commit date
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.gitignore		.gitignore
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE		LICENSE
README.md		README.md

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Swift 5 Cheatsheet

How to Use

Contributing

Table Of Contents

Variables

Functions

Operators

Classes, Objects, Properties

Structs

Protocols

Control Flow

Conditionals

Loops

Switch

Strings

Optionals

Collections

Arrays

Dictionaries

Sets

Closures

Guard and Defer

Guard

Defer

Generics

Tuples

Enumerations

Error Handling

Commenting

Comment Syntax

Resources

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