The Official raywenderlich.com Swift Style Guide.

Overview

The Official raywenderlich.com Swift Style Guide.

Updated for Swift 5

This style guide is different from others you may see, because the focus is centered on readability for print and the web. We created this style guide to keep the code in our books, tutorials, and starter kits nice and consistent — even though we have many different authors working on the books.

Our overarching goals are clarity, consistency and brevity, in that order.

Table of Contents

Correctness

Strive to make your code compile without warnings. This rule informs many style decisions such as using #selector types instead of string literals.

Using SwiftLint

When writing for raywenderlich.com, you are strongly encouraged — and some teams may require — to use our SwiftLint configuration. See the SwiftLint Policy for more information.

Naming

Descriptive and consistent naming makes software easier to read and understand. Use the Swift naming conventions described in the API Design Guidelines. Some key takeaways include:

  • striving for clarity at the call site
  • prioritizing clarity over brevity
  • using camelCase (not snake_case)
  • using UpperCamelCase for types and protocols, lowerCamelCase for everything else
  • including all needed words while omitting needless words
  • using names based on roles, not types
  • sometimes compensating for weak type information
  • striving for fluent usage
  • beginning factory methods with make
  • naming methods for their side effects
    • verb methods follow the -ed, -ing rule for the non-mutating version
    • noun methods follow the formX rule for the mutating version
    • boolean types should read like assertions
    • protocols that describe what something is should read as nouns
    • protocols that describe a capability should end in -able or -ible
  • using terms that don't surprise experts or confuse beginners
  • generally avoiding abbreviations
  • using precedent for names
  • preferring methods and properties to free functions
  • casing acronyms and initialisms uniformly up or down
  • giving the same base name to methods that share the same meaning
  • avoiding overloads on return type
  • choosing good parameter names that serve as documentation
  • preferring to name the first parameter instead of including its name in the method name, except as mentioned under Delegates
  • labeling closure and tuple parameters
  • taking advantage of default parameters

Prose

When referring to methods in prose, being unambiguous is critical. To refer to a method name, use the simplest form possible.

  1. Write the method name with no parameters. Example: Next, you need to call addTarget.
  2. Write the method name with argument labels. Example: Next, you need to call addTarget(_:action:).
  3. Write the full method name with argument labels and types. Example: Next, you need to call addTarget(_: Any?, action: Selector?).

For the above example using UIGestureRecognizer, 1 is unambiguous and preferred.

Pro Tip: You can use Xcode's jump bar to lookup methods with argument labels. If you’re particularly good at mashing lots of keys simultaneously, put the cursor in the method name and press Shift-Control-Option-Command-C (all 4 modifier keys) and Xcode will kindly put the signature on your clipboard.

Methods in Xcode jump bar

Class Prefixes

Swift types are automatically namespaced by the module that contains them and you should not add a class prefix such as RW. If two names from different modules collide you can disambiguate by prefixing the type name with the module name. However, only specify the module name when there is possibility for confusion, which should be rare.

import SomeModule

let myClass = MyModule.UsefulClass()

Delegates

When creating custom delegate methods, an unnamed first parameter should be the delegate source. (UIKit contains numerous examples of this.)

Preferred:

func namePickerView(_ namePickerView: NamePickerView, didSelectName name: String)
func namePickerViewShouldReload(_ namePickerView: NamePickerView) -> Bool

Not Preferred:

func didSelectName(namePicker: NamePickerViewController, name: String)
func namePickerShouldReload() -> Bool

Use Type Inferred Context

Use compiler inferred context to write shorter, clear code. (Also see Type Inference.)

Preferred:

let selector = #selector(viewDidLoad)
view.backgroundColor = .red
let toView = context.view(forKey: .to)
let view = UIView(frame: .zero)

Not Preferred:

let selector = #selector(ViewController.viewDidLoad)
view.backgroundColor = UIColor.red
let toView = context.view(forKey: UITransitionContextViewKey.to)
let view = UIView(frame: CGRect.zero)

Generics

Generic type parameters should be descriptive, upper camel case names. When a type name doesn't have a meaningful relationship or role, use a traditional single uppercase letter such as T, U, or V.

Preferred:

struct Stack<Element> { ... }
func write<Target: OutputStream>(to target: inout Target)
func swap<T>(_ a: inout T, _ b: inout T)

Not Preferred:

struct Stack<T> { ... }
func write<target: OutputStream>(to target: inout target)
func swap<Thing>(_ a: inout Thing, _ b: inout Thing)

Language

Use US English spelling to match Apple's API.

Preferred:

let color = "red"

Not Preferred:

let colour = "red"

Code Organization

Use extensions to organize your code into logical blocks of functionality. Each extension should be set off with a // MARK: - comment to keep things well-organized.

Protocol Conformance

In particular, when adding protocol conformance to a model, prefer adding a separate extension for the protocol methods. This keeps the related methods grouped together with the protocol and can simplify instructions to add a protocol to a class with its associated methods.

Preferred:

class MyViewController: UIViewController {
  // class stuff here
}

// MARK: - UITableViewDataSource
extension MyViewController: UITableViewDataSource {
  // table view data source methods
}

// MARK: - UIScrollViewDelegate
extension MyViewController: UIScrollViewDelegate {
  // scroll view delegate methods
}

Not Preferred:

class MyViewController: UIViewController, UITableViewDataSource, UIScrollViewDelegate {
  // all methods
}

Since the compiler does not allow you to re-declare protocol conformance in a derived class, it is not always required to replicate the extension groups of the base class. This is especially true if the derived class is a terminal class and a small number of methods are being overridden. When to preserve the extension groups is left to the discretion of the author.

For UIKit view controllers, consider grouping lifecycle, custom accessors, and IBAction in separate class extensions.

Unused Code

Unused (dead) code, including Xcode template code and placeholder comments should be removed. An exception is when your tutorial or book instructs the user to use the commented code.

Aspirational methods not directly associated with the tutorial whose implementation simply calls the superclass should also be removed. This includes any empty/unused UIApplicationDelegate methods.

Preferred:

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
  return Database.contacts.count
}

Not Preferred:

override func didReceiveMemoryWarning() {
  super.didReceiveMemoryWarning()
  // Dispose of any resources that can be recreated.
}

override func numberOfSections(in tableView: UITableView) -> Int {
  // #warning Incomplete implementation, return the number of sections
  return 1
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
  // #warning Incomplete implementation, return the number of rows
  return Database.contacts.count
}

Minimal Imports

Import only the modules a source file requires. For example, don't import UIKit when importing Foundation will suffice. Likewise, don't import Foundation if you must import UIKit.

Preferred:

import UIKit
var view: UIView
var deviceModels: [String]

Preferred:

import Foundation
var deviceModels: [String]

Not Preferred:

import UIKit
import Foundation
var view: UIView
var deviceModels: [String]

Not Preferred:

import UIKit
var deviceModels: [String]

Spacing

  • Indent using 2 spaces rather than tabs to conserve space and help prevent line wrapping. Be sure to set this preference in Xcode and in the Project settings as shown below:

Xcode indent settings

  • Method braces and other braces (if/else/switch/while etc.) always open on the same line as the statement but close on a new line.
  • Tip: You can re-indent by selecting some code (or Command-A to select all) and then Control-I (or Editor ▸ Structure ▸ Re-Indent in the menu). Some of the Xcode template code will have 4-space tabs hard coded, so this is a good way to fix that.

Preferred:

if user.isHappy {
  // Do something
} else {
  // Do something else
}

Not Preferred:

if user.isHappy
{
  // Do something
}
else {
  // Do something else
}
  • There should be one blank line between methods and up to one blank line between type declarations to aid in visual clarity and organization. Whitespace within methods should separate functionality, but having too many sections in a method often means you should refactor into several methods.

  • There should be no blank lines after an opening brace or before a closing brace.

  • Colons always have no space on the left and one space on the right. Exceptions are the ternary operator ? :, empty dictionary [:] and #selector syntax addTarget(_:action:).

Preferred:

class TestDatabase: Database {
  var data: [String: CGFloat] = ["A": 1.2, "B": 3.2]
}

Not Preferred:

class TestDatabase : Database {
  var data :[String:CGFloat] = ["A" : 1.2, "B":3.2]
}
  • Long lines should be wrapped at around 70 characters. A hard limit is intentionally not specified.

  • Avoid trailing whitespaces at the ends of lines.

  • Add a single newline character at the end of each file.

Comments

When they are needed, use comments to explain why a particular piece of code does something. Comments must be kept up-to-date or deleted.

Avoid block comments inline with code, as the code should be as self-documenting as possible. Exception: This does not apply to those comments used to generate documentation.

Avoid the use of C-style comments (/* ... */). Prefer the use of double- or triple-slash.

Classes and Structures

Which one to use?

Remember, structs have value semantics. Use structs for things that do not have an identity. An array that contains [a, b, c] is really the same as another array that contains [a, b, c] and they are completely interchangeable. It doesn't matter whether you use the first array or the second, because they represent the exact same thing. That's why arrays are structs.

Classes have reference semantics. Use classes for things that do have an identity or a specific life cycle. You would model a person as a class because two person objects are two different things. Just because two people have the same name and birthdate, doesn't mean they are the same person. But the person's birthdate would be a struct because a date of 3 March 1950 is the same as any other date object for 3 March 1950. The date itself doesn't have an identity.

Sometimes, things should be structs but need to conform to AnyObject or are historically modeled as classes already (NSDate, NSSet). Try to follow these guidelines as closely as possible.

Example definition

Here's an example of a well-styled class definition:

class Circle: Shape {
  var x: Int, y: Int
  var radius: Double
  var diameter: Double {
    get {
      return radius * 2
    }
    set {
      radius = newValue / 2
    }
  }

  init(x: Int, y: Int, radius: Double) {
    self.x = x
    self.y = y
    self.radius = radius
  }

  convenience init(x: Int, y: Int, diameter: Double) {
    self.init(x: x, y: y, radius: diameter / 2)
  }

  override func area() -> Double {
    return Double.pi * radius * radius
  }
}

extension Circle: CustomStringConvertible {
  var description: String {
    return "center = \(centerString) area = \(area())"
  }
  private var centerString: String {
    return "(\(x),\(y))"
  }
}

The example above demonstrates the following style guidelines:

  • Specify types for properties, variables, constants, argument declarations and other statements with a space after the colon but not before, e.g. x: Int, and Circle: Shape.
  • Define multiple variables and structures on a single line if they share a common purpose / context.
  • Indent getter and setter definitions and property observers.
  • Don't add modifiers such as internal when they're already the default. Similarly, don't repeat the access modifier when overriding a method.
  • Organize extra functionality (e.g. printing) in extensions.
  • Hide non-shared, implementation details such as centerString inside the extension using private access control.

Use of Self

For conciseness, avoid using self since Swift does not require it to access an object's properties or invoke its methods.

Use self only when required by the compiler (in @escaping closures, or in initializers to disambiguate properties from arguments). In other words, if it compiles without self then omit it.

Computed Properties

For conciseness, if a computed property is read-only, omit the get clause. The get clause is required only when a set clause is provided.

Preferred:

var diameter: Double {
  return radius * 2
}

Not Preferred:

var diameter: Double {
  get {
    return radius * 2
  }
}

Final

Marking classes or members as final in tutorials can distract from the main topic and is not required. Nevertheless, use of final can sometimes clarify your intent and is worth the cost. In the below example, Box has a particular purpose and customization in a derived class is not intended. Marking it final makes that clear.

// Turn any generic type into a reference type using this Box class.
final class Box<T> {
  let value: T
  init(_ value: T) {
    self.value = value
  }
}

Function Declarations

Keep short function declarations on one line including the opening brace:

func reticulateSplines(spline: [Double]) -> Bool {
  // reticulate code goes here
}

For functions with long signatures, put each parameter on a new line and add an extra indent on subsequent lines:

func reticulateSplines(
  spline: [Double], 
  adjustmentFactor: Double,
  translateConstant: Int, 
  comment: String
) -> Bool {
  // reticulate code goes here
}

Don't use (Void) to represent the lack of an input; simply use (). Use Void instead of () for closure and function outputs.

Preferred:

func updateConstraints() -> Void {
  // magic happens here
}

typealias CompletionHandler = (result) -> Void

Not Preferred:

func updateConstraints() -> () {
  // magic happens here
}

typealias CompletionHandler = (result) -> ()

Function Calls

Mirror the style of function declarations at call sites. Calls that fit on a single line should be written as such:

let success = reticulateSplines(splines)

If the call site must be wrapped, put each parameter on a new line, indented one additional level:

let success = reticulateSplines(
  spline: splines,
  adjustmentFactor: 1.3,
  translateConstant: 2,
  comment: "normalize the display")

Closure Expressions

Use trailing closure syntax only if there's a single closure expression parameter at the end of the argument list. Give the closure parameters descriptive names.

Preferred:

UIView.animate(withDuration: 1.0) {
  self.myView.alpha = 0
}

UIView.animate(withDuration: 1.0, animations: {
  self.myView.alpha = 0
}, completion: { finished in
  self.myView.removeFromSuperview()
})

Not Preferred:

UIView.animate(withDuration: 1.0, animations: {
  self.myView.alpha = 0
})

UIView.animate(withDuration: 1.0, animations: {
  self.myView.alpha = 0
}) { f in
  self.myView.removeFromSuperview()
}

For single-expression closures where the context is clear, use implicit returns:

attendeeList.sort { a, b in
  a > b
}

Chained methods using trailing closures should be clear and easy to read in context. Decisions on spacing, line breaks, and when to use named versus anonymous arguments is left to the discretion of the author. Examples:

let value = numbers.map { $0 * 2 }.filter { $0 % 3 == 0 }.index(of: 90)

let value = numbers
  .map {$0 * 2}
  .filter {$0 > 50}
  .map {$0 + 10}

Types

Always use Swift's native types and expressions when available. Swift offers bridging to Objective-C so you can still use the full set of methods as needed.

Preferred:

let width = 120.0                                    // Double
let widthString = "\(width)"                         // String

Less Preferred:

let width = 120.0                                    // Double
let widthString = (width as NSNumber).stringValue    // String

Not Preferred:

let width: NSNumber = 120.0                          // NSNumber
let widthString: NSString = width.stringValue        // NSString

In drawing code, use CGFloat if it makes the code more succinct by avoiding too many conversions.

Constants

Constants are defined using the let keyword and variables with the var keyword. Always use let instead of var if the value of the variable will not change.

Tip: A good technique is to define everything using let and only change it to var if the compiler complains!

You can define constants on a type rather than on an instance of that type using type properties. To declare a type property as a constant simply use static let. Type properties declared in this way are generally preferred over global constants because they are easier to distinguish from instance properties. Example:

Preferred:

enum Math {
  static let e = 2.718281828459045235360287
  static let root2 = 1.41421356237309504880168872
}

let hypotenuse = side * Math.root2

Note: The advantage of using a case-less enumeration is that it can't accidentally be instantiated and works as a pure namespace.

Not Preferred:

let e = 2.718281828459045235360287  // pollutes global namespace
let root2 = 1.41421356237309504880168872

let hypotenuse = side * root2 // what is root2?

Static Methods and Variable Type Properties

Static methods and type properties work similarly to global functions and global variables and should be used sparingly. They are useful when functionality is scoped to a particular type or when Objective-C interoperability is required.

Optionals

Declare variables and function return types as optional with ? where a nil value is acceptable.

Use implicitly unwrapped types declared with ! only for instance variables that you know will be initialized later before use, such as subviews that will be set up in viewDidLoad(). Prefer optional binding to implicitly unwrapped optionals in most other cases.

When accessing an optional value, use optional chaining if the value is only accessed once or if there are many optionals in the chain:

textContainer?.textLabel?.setNeedsDisplay()

Use optional binding when it's more convenient to unwrap once and perform multiple operations:

if let textContainer = textContainer {
  // do many things with textContainer
}

When naming optional variables and properties, avoid naming them like optionalString or maybeView since their optional-ness is already in the type declaration.

For optional binding, shadow the original name whenever possible rather than using names like unwrappedView or actualLabel.

Preferred:

var subview: UIView?
var volume: Double?

// later on...
if let subview = subview, let volume = volume {
  // do something with unwrapped subview and volume
}

// another example
resource.request().onComplete { [weak self] response in
  guard let self = self else { return }
  let model = self.updateModel(response)
  self.updateUI(model)
}

Not Preferred:

var optionalSubview: UIView?
var volume: Double?

if let unwrappedSubview = optionalSubview {
  if let realVolume = volume {
    // do something with unwrappedSubview and realVolume
  }
}

// another example
UIView.animate(withDuration: 2.0) { [weak self] in
  guard let strongSelf = self else { return }
  strongSelf.alpha = 1.0
}

Lazy Initialization

Consider using lazy initialization for finer grained control over object lifetime. This is especially true for UIViewController that loads views lazily. You can either use a closure that is immediately called { }() or call a private factory method. Example:

lazy var locationManager = makeLocationManager()

private func makeLocationManager() -> CLLocationManager {
  let manager = CLLocationManager()
  manager.desiredAccuracy = kCLLocationAccuracyBest
  manager.delegate = self
  manager.requestAlwaysAuthorization()
  return manager
}

Notes:

  • [unowned self] is not required here. A retain cycle is not created.
  • Location manager has a side-effect for popping up UI to ask the user for permission so fine grain control makes sense here.

Type Inference

Prefer compact code and let the compiler infer the type for constants or variables of single instances. Type inference is also appropriate for small, non-empty arrays and dictionaries. When required, specify the specific type such as CGFloat or Int16.

Preferred:

let message = "Click the button"
let currentBounds = computeViewBounds()
var names = ["Mic", "Sam", "Christine"]
let maximumWidth: CGFloat = 106.5

Not Preferred:

let message: String = "Click the button"
let currentBounds: CGRect = computeViewBounds()
var names = [String]()

Type Annotation for Empty Arrays and Dictionaries

For empty arrays and dictionaries, use type annotation. (For an array or dictionary assigned to a large, multi-line literal, use type annotation.)

Preferred:

var names: [String] = []
var lookup: [String: Int] = [:]

Not Preferred:

var names = [String]()
var lookup = [String: Int]()

NOTE: Following this guideline means picking descriptive names is even more important than before.

Syntactic Sugar

Prefer the shortcut versions of type declarations over the full generics syntax.

Preferred:

var deviceModels: [String]
var employees: [Int: String]
var faxNumber: Int?

Not Preferred:

var deviceModels: Array<String>
var employees: Dictionary<Int, String>
var faxNumber: Optional<Int>

Functions vs Methods

Free functions, which aren't attached to a class or type, should be used sparingly. When possible, prefer to use a method instead of a free function. This aids in readability and discoverability.

Free functions are most appropriate when they aren't associated with any particular type or instance.

Preferred

let sorted = items.mergeSorted()  // easily discoverable
rocket.launch()  // acts on the model

Not Preferred

let sorted = mergeSort(items)  // hard to discover
launch(&rocket)

Free Function Exceptions

let tuples = zip(a, b)  // feels natural as a free function (symmetry)
let value = max(x, y, z)  // another free function that feels natural

Memory Management

Code (even non-production, tutorial demo code) should not create reference cycles. Analyze your object graph and prevent strong cycles with weak and unowned references. Alternatively, use value types (struct, enum) to prevent cycles altogether.

Extending object lifetime

Extend object lifetime using the [weak self] and guard let self = self else { return } idiom. [weak self] is preferred to [unowned self] where it is not immediately obvious that self outlives the closure. Explicitly extending lifetime is preferred to optional chaining.

Preferred

resource.request().onComplete { [weak self] response in
  guard let self = self else {
    return
  }
  let model = self.updateModel(response)
  self.updateUI(model)
}

Not Preferred

// might crash if self is released before response returns
resource.request().onComplete { [unowned self] response in
  let model = self.updateModel(response)
  self.updateUI(model)
}

Not Preferred

// deallocate could happen between updating the model and updating UI
resource.request().onComplete { [weak self] response in
  let model = self?.updateModel(response)
  self?.updateUI(model)
}

Access Control

Full access control annotation in tutorials can distract from the main topic and is not required. Using private and fileprivate appropriately, however, adds clarity and promotes encapsulation. Prefer private to fileprivate; use fileprivate only when the compiler insists.

Only explicitly use open, public, and internal when you require a full access control specification.

Use access control as the leading property specifier. The only things that should come before access control are the static specifier or attributes such as @IBAction, @IBOutlet and @discardableResult.

Preferred:

private let message = "Great Scott!"

class TimeMachine {  
  private dynamic lazy var fluxCapacitor = FluxCapacitor()
}

Not Preferred:

fileprivate let message = "Great Scott!"

class TimeMachine {  
  lazy dynamic private var fluxCapacitor = FluxCapacitor()
}

Control Flow

Prefer the for-in style of for loop over the while-condition-increment style.

Preferred:

for _ in 0..<3 {
  print("Hello three times")
}

for (index, person) in attendeeList.enumerated() {
  print("\(person) is at position #\(index)")
}

for index in stride(from: 0, to: items.count, by: 2) {
  print(index)
}

for index in (0...3).reversed() {
  print(index)
}

Not Preferred:

var i = 0
while i < 3 {
  print("Hello three times")
  i += 1
}


var i = 0
while i < attendeeList.count {
  let person = attendeeList[i]
  print("\(person) is at position #\(i)")
  i += 1
}

Ternary Operator

The Ternary operator, ?: , should only be used when it increases clarity or code neatness. A single condition is usually all that should be evaluated. Evaluating multiple conditions is usually more understandable as an if statement or refactored into instance variables. In general, the best use of the ternary operator is during assignment of a variable and deciding which value to use.

Preferred:

let value = 5
result = value != 0 ? x : y

let isHorizontal = true
result = isHorizontal ? x : y

Not Preferred:

result = a > b ? x = c > d ? c : d : y

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.

Preferred:

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
}

Not Preferred:

func computeFFT(context: Context?, inputData: InputData?) throws -> Frequencies {
  if let context = context {
    if let inputData = inputData {
      // use context and input to compute the frequencies

      return frequencies
    } else {
      throw FFTError.noInputData
    }
  } else {
    throw FFTError.noContext
  }
}

When multiple optionals are unwrapped either with guard or if let, minimize nesting by using the compound version when possible. In the compound version, place the guard on its own line, then indent each condition on its own line. The else clause is indented to match the guard itself, as shown below. Example:

Preferred:

guard 
  let number1 = number1,
  let number2 = number2,
  let number3 = number3 
else {
  fatalError("impossible")
}
// do something with numbers

Not Preferred:

if let number1 = number1 {
  if let number2 = number2 {
    if let number3 = number3 {
      // do something with numbers
    } else {
      fatalError("impossible")
    }
  } else {
    fatalError("impossible")
  }
} else {
  fatalError("impossible")
}

Failing Guards

Guard statements are required to exit in some way. Generally, this should be simple one line statement such as return, throw, break, continue, and fatalError(). Large code blocks should be avoided. If cleanup code is required for multiple exit points, consider using a defer block to avoid cleanup code duplication.

Semicolons

Swift does not require a semicolon after each statement in your code. They are only required if you wish to combine multiple statements on a single line.

Do not write multiple statements on a single line separated with semicolons.

Preferred:

let swift = "not a scripting language"

Not Preferred:

let swift = "not a scripting language";

NOTE: Swift is very different from JavaScript, where omitting semicolons is generally considered unsafe

Parentheses

Parentheses around conditionals are not required and should be omitted.

Preferred:

if name == "Hello" {
  print("World")
}

Not Preferred:

if (name == "Hello") {
  print("World")
}

In larger expressions, optional parentheses can sometimes make code read more clearly.

Preferred:

let playerMark = (player == current ? "X" : "O")

Multi-line String Literals

When building a long string literal, you're encouraged to use the multi-line string literal syntax. Open the literal on the same line as the assignment but do not include text on that line. Indent the text block one additional level.

Preferred:

let message = """
  You cannot charge the flux \
  capacitor with a 9V battery.
  You must use a super-charger \
  which costs 10 credits. You currently \
  have \(credits) credits available.
  """

Not Preferred:

let message = """You cannot charge the flux \
  capacitor with a 9V battery.
  You must use a super-charger \
  which costs 10 credits. You currently \
  have \(credits) credits available.
  """

Not Preferred:

let message = "You cannot charge the flux " +
  "capacitor with a 9V battery.\n" +
  "You must use a super-charger " +
  "which costs 10 credits. You currently " +
  "have \(credits) credits available."

No Emoji

Do not use emoji in your projects. For those readers who actually type in their code, it's an unnecessary source of friction. While it may be cute, it doesn't add to the learning and it interrupts the coding flow for these readers.

No #imageLiteral or #colorLiteral

Likewise, do not use Xcode's ability to drag a color or an image into a source statement. These turn into #colorLiteral and #imageLiteral, respectively, and present unpleasant challenges for a reader trying to enter them based on tutorial text. Instead, use UIColor(red:green:blue) and UIImage(imageLiteralResourceName:).

Organization and Bundle Identifier

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Smiley Face

Smiley faces are a very prominent style feature of the raywenderlich.com site! It is very important to have the correct smile signifying the immense amount of happiness and excitement for the coding topic. The closing square bracket ] is used because it represents the largest smile able to be captured using ASCII art. A closing parenthesis ) creates a half-hearted smile, and thus is not preferred.

Preferred:

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Not Preferred:

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References

Comments
  • Preferred for-loop type

    Preferred for-loop type

    As different people may have different preferences, I think that a standard for-loop type across all the site's materials would be best, instead of having different types used in different places. For example, both these are the same:

    for var i = 0; i < 10; ++i{
        println(i)
    }
    
    for j in 0..10{
        println(j)
    }
    

    The second seems to be the preferred loop by Apple, and has several benefits:

    • Not as long (for books this is helpful)
    • Easier to look at (the var, semicolons, and math characters are gone)
    • Easier to understand quickly (in my opinion, less clutter than the first– might be just me)
    • Can take ranges created by .. and ... (very convenient)
    • Can use an underscore if the value is not needed

    There are likely circumstances that the first would need (or want) to be used, but generally, I feel this new Swift for-loop syntax is the style we should adopt.

    Nothing says that we need to standardize the for-loop syntax. I think doing so would help to make the code more consistent.

    Just to keep track, certain cases where the first solution still is needed:

    • counting backwards (no 10..0)
    • counting by 2's (or other integers)
    • floats

    I'll try keeping this updated when new cases come to mind.

    opened by edekhayser 30
  • Lazy initializing pattern

    Lazy initializing pattern

    A lot of us in tutorials these days are using patterns like this to initialize variables:

    lazy var locationManager: CLLocationManager = {
        let manager = CLLocationManager()
        manager.desiredAccuracy = kCLLocationAccuracyBest
        manager.delegate = self
        manager.requestAlwaysAuthorization()
        return manager
      }()
    

    I've seen this for setting up controls like UILabels and such too. This has the advantage of keeping the initialization code in one handy place.

    I thought I'd start a discussion to see if this is a pattern we want to encourage in the style guide?

    opened by rwenderlich 29
  • Using self

    Using self

    While writing Swift code, I catch myself typing self.propertyName and self.method() a lot. But in Swift (as in C++, C# and Java) using self is not necessary unless you're trying to resolve an ambiguous situation.

    I suggest we don't use self except for that purpose.

    opened by hollance 28
  • new struct inits over old C functions

    new struct inits over old C functions

    I think that all new code (or code that's being updated) should use the new struct initializers.

    I personally never liked CGPointMake() and am now glad that I can write CGPoint(x: 10, y: 20) - it is much much much more readable.

    So:

    • CGPoint(x:, y:) over CGPointMake
    • CGSize(width:, height:) over CGSizeMake
    • CGRect(x:, y:, width:, height:) over CGRectMake

    How does the rest of you feel about that? If "yes, that's awesome" - anymore examples we need to highlight?

    And yeah - I know that Apple might change the underlying structure for CGPoint, but I think we should stop living and fear and assume that a point is gonna be made of an X and a Y in at least our lifetime.

    opened by icanzilb 27
  • Functions vs. Methods

    Functions vs. Methods

    The guide should be explicit about the appropriate use of function and method when writing. Having taken a look at Apple's Swift Programming Language docs, something like:

    A method is a function that's associated with a class, struct, or enum. This goes for both instance and type methods. A function, on the other hand, is declared in the global scope and doesn't belong to any type.

    would be sufficient.

    opened by ghost 26
  • Variable shadowing can lead to harder-to-read code.

    Variable shadowing can lead to harder-to-read code.

    I think we should reconsider our position on using shadow variables when unwrapping. Our current argument is that the compiler will correct you if you try to use the wrong variable. I think there's a fundamental flaw in that argument that we've overlooked: It makes code significantly harder to read when not actually being compiled.

    I see three major places where reading code like this outside of a compiler causes problems:

    1. Swift beginners. It's very confusing for two things with the same name to have such fundamentally different behavior. This is particularly true for those of us coming from Objective-C, where trying to define two things with the same name causes a compiler warning.
    2. Code reviews. For anyone who has to look through code before it gets merged down, there's an extra level of scrutiny required to make sure "wait, is this person trying to assign the optional or the unwrapped value?"
    3. Book editing. Are we expecting all of our book editors to take not just the sample code but any code typed in the book whatsoever and ensure that it compiles?

    Take this example:

    func createNewPerson(name: String?) -> Person {
      let person = Person()
      if let name = name {
        person.name = name
      }
     return person
    }
    

    Without compiling that code, how do I know that the name variable being set is the unwrapped one rather than the passed-in optional?

    This is what I've been doing in my Swift code in a similar situation:

    func createNewPerson(name: String?) -> Person {
      let person = Person()
      if let unwrappedName = name {
        person.name = unwrappedName
      }
     return person
    }
    

    For me, simply adding unwrapped to the unwrapped variable name makes the flow of the code significantly clearer. We don't have to use that exact syntax (especially since it makes variable names so much longer), but I do think we should reconsider shadowing variables for this reason.

    OK, now that I've made my case: FIGHT FIGHT FIGHT FIGHT FIGHT!

    1tpffru

    opened by designatednerd 22
  • Discussion: suppressing external names for initialisers

    Discussion: suppressing external names for initialisers

    Personally I really dislike the way that all parameters names for initialisers are external by default, e.g.:

    struct BoardLocation {
      init(row: Int,column: Int) {
        ...
      }
    }
    
    let location = BoardLocation(row: 2, column: 3)
    

    These can be suppressed with an underscore as follows:

    struct BoardLocation {
      init(_ row: Int,_ column: Int) {
        ...
      }
    }
    
    let location = BoardLocation(2, 3)
    

    What are people's thoughts on this? Personally i like it.

    opened by ColinEberhardt 22
  • How to name functions when you're writing about them

    How to name functions when you're writing about them

    I just updated my Candy Crush tutorial to Swift and found that referencing function names from the text can be awkward.

    For example, I have the method:

    func convertPointFromColumn(column: Int, row: Int) -> CGPoint
    

    This uses the style where the first argument is named as part of the function name.

    So in the text, should I refer to this as:

    • convertPointFromColumn()
    • convertPointFromColumn(row:)
    • convertPointFromColumn(column:, row:)

    The first one is the shortest but also incomplete because row: is part of the function name.

    The second one might be misleading because a reader may think row: is the argument, not part of the name.

    The third one is the most correct, but also the longest and "noisiest".

    Note that Xcode calls this method convertPointFromColumn(_, row:). That's also an option but not a very nice one...

    opened by hollance 21
  • Variable name for Optional Binding

    Variable name for Optional Binding

    To use the value of an optional property, we can use Optional Binding. For example:

    if let t = self.title {
      // do many things with title
    }
    

    But I'm always confused about the naming of the optionally bounded variable. In the case above, how should the variable t be named? Using the first letter is of course very bad!

    Any ideas?

    opened by ishuo 19
  • Method naming style inconsistent with Swift book

    Method naming style inconsistent with Swift book

    From Apple's Swift Book:

    “As in Objective-C, the name of a method in Swift typically refers to the method’s first parameter using a preposition such as with, for, or by, as seen in the incrementBy(_:) method from the preceding Counter class example. The use of a preposition enables the method to be read as a sentence when it is called.”

    Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. https://itun.es/us/jEUH0.l

    Thus, I think our method naming style is inconsistent such that upvoteBy(amount: Int) matches Apple's recommendation, but combineWithString(incoming: String, options: Dictionary?) should be combineWith(incoming: String, options: Dictionary?)

    If ya'll okay with this change, I can submit a PR.

    opened by obuseme 17
  • Golden Path

    Golden Path

    To steal from our Objective-C style guide, I propose the inclusion of the Golden Path rule in this guide:

    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.

    Preferred:

    func someMethod() {
    
      if someBoolValue == false {
        return
      }
    
      // Do something important
    }
    

    Not Preferred:

    func someMethod() {
    
      if someBoolValue == true {
        // Do something important
      }
    }
    
    enhancement 
    opened by JRG-Developer 17
  • False positive from array_constructor custom rule

    False positive from array_constructor custom rule

    https://github.com/raywenderlich/swift-style-guide/blob/88701838883776b8dafcbefff5120161dcd8c0c3/com.raywenderlich.swiftlint.yml#L56

    The intent of the regex pattern in custom rule, array_constructor is to catch something like let foo = [String](), however, it's causing a false positive on a properly initialized array like let foo = [Bar()].

    opened by moayes 0
  • Please add `no_extension_access_modifier` as a default SwiftLint rule

    Please add `no_extension_access_modifier` as a default SwiftLint rule

    To consider adding one extra rule for SwiftLint default set: https://realm.github.io/SwiftLint/no_extension_access_modifier.html

    That's recommended by Google swift guideline (Access Levels section at https://google.github.io/swift/#programming-practices )and personally, I find it useful.

    opened by ppave 1
  • Exclusionary Language

    Exclusionary Language

    We've based our style guide on this Swift style guide (thank you to the maintainers and all the contributors, btw) so while figuring out how to address the use of exclusionary language in our style guide I came here to see if I could find inspiration. Since I don't see anything in this style guide or any recent issues I'd like to prompt a discussion -- would it make sense to add style rules for avoiding exclusionary language to the naming discussion in the style guide or perhaps to its own section of the document?

    For context, I mean exclusionary language in the way it is used in this Apple Developer news item: https://developer.apple.com/news/?id=1o9zxsxl

    opened by DavidBrunow 1
  • Some proposed allowable exceptions to SwiftLint rules

    Some proposed allowable exceptions to SwiftLint rules

    Code generated by Xcode should be treated like open source files, and have a disable-all added at the top. I'm thinking particularly of core data property generated files, which are never touched by the user.

    Code in unit tests should be allowed to use IUOs, since test code is dealing with known state and defensive coding would often add too much noise and detract from the meaning of the tests.

    opened by jrturton 0
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