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.

> 우리의 가장 중요한 목표는 선명도, 일관성, 간결성 입니다.

• Correctness
• Naming
  • Prose
  • Delegates
  • Use Type Inferred Context
  • Generics
  • Class Prefixes
  • Language
• Code Organization
  • Protocol Conformance
  • Unused Code
  • Minimal Imports
• Spacing
• Comments
• Classes and Structures
  • Use of Self
  • Protocol Conformance
  • Computed Properties
  • Final
• Function Declarations
• Function Calls
• Closure Expressions
• Types
  • Constants
  • Static Methods and Variable Type Properties
  • Optionals
  • Lazy Initialization
  • Type Inference
  • Syntactic Sugar
• Functions vs Methods
• Memory Management
  • Extending Lifetime
• Access Control
• Control Flow
  • Ternary Operator
• Golden Path
  • Failing Guards
• Semicolons
• Parentheses
• Multi-line String Literals
• No Emoji
• Organization and Bundle Identifier
• Copyright Statement
• Smiley Face
• References

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

> 당신의 코드를 컴파일 할때, 경고(warning)가 없도록 노력하세요.

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

> 설명적이고 일관된 네이밍은 소프트웨어를 읽고 이해하는 것을 더 쉽게 만듭니다. 스위프트 네이밍 컨벤션들을 사용하세요.

Some key takeaways include:

• striving for clarity at the call site

> 콜 사이트에서 명확하게 하기 위해 노력하세요.

• prioritizing clarity over brevity

> 간결함 보다는 우선순위를 명확하게 하세요.

• using camel case (not snake case)

> 카멜케이스를 사용하세요.
ex: camelCase (o), CamelCase (x) camel_case (x)

• using uppercase for types (and protocols), lowercase for everything else

> 타입, 프로토콜에는 대문자를 사용하고, 나머지는 모두 소문자를 사용하세요.

• including all needed words while omitting needless words

> 불필요한 단어를 생략하고, 필요한 모든 단어를 포함시키세요.

• using names based on roles, not types

> 타입이 아닌 역할에 기반한 이름을 사용하세요.

• sometimes compensating for weak type information

> 때때로 weak 타입 정보를 보충하세요.

• striving for fluent usage

> 유창한 사용을 위해 노력하세요.

• beginning factory methods with make

> *팩토리 메소드는 make로 시작하세요.
*객체를 만들어내는 부분을 서브 클래스Sub-Class에 위임하는 패턴.

• naming methods for their side effects

  • verb methods follow the -ed, -ing rule for the non-mutating version

  > 동사 메소드는 -ed, -ing 규칙을 따릅니다.
  

  • noun methods follow the formX rule for the mutating version

  > 명사 메소드는 mutating version을 위해 formX 규칙을 따릅니다.
  

  • boolean types should read like assertions

  > 부울런 타입은 assertions 처럼 읽어야 합니다.
  

  • protocols that describe what something is should read as nouns

  > 무언가를 나타내는 프로토콜은 명사로 나타냅니다.
  

  • protocols that describe a capability should end in -able or -ible

  > 무언가를 하는 프로토콜은 -able, -ible 접미사를 붙여 나타냅니다.
  

• using terms that don't surprise experts or confuse beginners

> 전문가가 놀라거나, 초보자가 혼동되지 않는 용어를 사용하세요.

• generally avoiding abbreviations

> 일반적으로 약어를 피하세요.

• using precedent for names

> 이름에 대해 선례를 사용합니다.

• preferring methods and properties to free functions

> 기능 해제를 위해 메소드들과 속성들을 선호하세요.

• casing acronyms and initialisms uniformly up or down

> 두문자어는 한결같이 사용하세요
ex: url (o), URL (o), Url(x), USA(o), usa(o), Usa(x)

• giving the same base name to methods that share the same meaning

> 동일한 의미를 공유하는 메소드에 동일한 이름을 부여하세요.

• avoiding overloads on return type

> 반환 타입에 대한 오버로드는 피하세요.

• choosing good parameter names that serve as documentation

> 문서로서 사용되는 좋은 매개 변수 이름을 선택하세요.

• preferring to name the first parameter instead of including its name in the method name, except as mentioned under Delegates

> 델리게이트에서 언급 한 경우를 제외하고 메서드 이름에 이름을 포함하는 대신 첫번째 매개변수의 이름을 지정하세요.

• labeling closure and tuple parameters

> 클로저와 튜플 매개변수들에 이름을 부여하세요.

• taking advantage of default parameters

> 기본 매개변수를 활용합니다.

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

> 산문의 방법을 언급 할 때 모호하지 않는 것이 중요합니다. 메서드 이름을 참조할때, 가능한 가장 간단한 형식을 사용하세요.

1. Write the method name with no parameters. Example: Next, you need to call addTarget.

> 매개변수없이 메소드 이름을 작성하세요.
ex: addTarget

2. Write the method name with argument labels. Example: Next, you need to call addTarget(_:action:).

> 매개변수 이름과 함께 메소드 이름을 작성하세요.
ex: addTarget(_:action:)

3. Write the full method name with argument labels and types. Example: Next, you need to call addTarget(_: Any?, action: Selector?).

> 매개변수의 이름과 타입을 가진 전체메소드 이름을 작성하세요.
ex: addTarget(_: Any?, action:)

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.

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.

> 스위프트 타입은 자동적으로 네임스페이스를 포함하는 모듈에 의해 네임스페이스가 지정되며, RW와 같은 클래스 접두사를 추가하면 안됩니다. 만약 충돌이 생기는 상황에서만 접두사를 사용하세요.

import SomeModule

let myClass = MyModule.UsefulClass()

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

> 커스텀 델리게이트 메소드를 생성할 때, 이름없는 첫번째 매개변수는 대리자 자신이여야 합니다. (UIKit에는 이에 대한 많은 예제가 있습니다.)

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

> 컴파일러로 부터 유추된 컨텍스트를 사용하여 짧고 명확한 코드를 작성하세요.

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)

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.

> 제네릭 타입 매개변수는 설명적인 카멜 케이스 이름이여야 합니다. 제네릭 타입 이름이 의미를 가지지 않는다면 T, U, V와 같이 하나의 대문자를 사용하세요.

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)

Use US English spelling to match Apple's API.

> US 영어 스펠링을 사용하여 Apple의 API와 일치 시키세요.

Preferred:

let color = "red"

Not Preferred:

let colour = "red"

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.

> extension을 사용하여 코드를 논리적인 기능 블록으로 구성하세요. 각 확장은 잘 정리 된 것을 유지하기 위해 "// MARK: - " 주석을 사용하세요.

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.

> 특히 모델에 프로토콜을 추가할 때, 프로토콜 메소드에 대해 별도의 extension을 사용하세요. 이는 관련 메소드를 프로토콜과 함께 그룹화 된 상태로 유지하고 관련된 메소드로 클래스에 프로토콜을 추가하는 지시를 단순화 할 수 있습니다.

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.

> UIKit의 ViewController에서, lifecycle, custom accessors, IBAction등을 extension 을 통해 그룹화 하는것을 고려하세요.

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.

> 사용하지 않는 코드는 제거하세요.

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
}

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.

> 소스파일에 필요한 모듈만 사용하세요.

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]

• 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:

> 공간을 절약하고 줄 바꿈을 방지하기 위해 탭 대신 2개의 스페이스(공백)을 사용하여 들여쓰기를 하세요.

• 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 exactly one blank line between methods 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.

> 시각적 명확성과 조직화를 돕기위해 메소드사이에 하나의 공백이 있어야 합니다. 메소드 내의 공백은 기능을 분리해야 하지만, 메소드 내에 너무 많은 섹션이 있으면 종종 여러 메소드로 리팩토링 해야만 합니다.

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

> 중괄호 뒤 또는 앞에는 공백이 있으면 안됩니다.

• 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:).

> 콜론(:)은 항상 왼쪽에는 공백이 없고 오른쪽에는 공백을 두어야 합니다. 예외는 삼항 연산자가 있습니다.

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.

> 한줄에 70자를 넘기지 마세요.

• Avoid trailing whitespaces at the ends of lines.

> 줄 끝에 공백을 피하세요.

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

> 각 파일의 끝에 단일 개행 문자를 추가하세요.

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.

> 주석을 사용하여 특정 코드가 왜 작동하는지 설명하세요. 가능한 한 코드 자체가 문서화 되어야 하므로 코드를 사용하여 주석을 블록하지 마세요. 마지막으로 C 스타일 주석 (/*...*/) 을 사용하지마세요. 이중 또는 삼중 슬래시를 사용하세요.

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.

> 기억하세요 struct는 값 타입입니다. identity를 가지지 않는 것엔 struct를 사용하세요.

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.

> 기억하세요 class는 레퍼런스 타입입니다. identity를 가지는 것엔 class를 사용하세요.

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.

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.

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.

> 스위프트는 객체의 속성에 접근하거나 메소드를 호출할 필요가 없기 때문에 'self'를 사용하지마세요. 컴파일러에서 필요할 때만 'self'를 사용합니다.

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.

> 간결성을 위해 computed Properties에 get 절을 생량하세요. get절은 set절이 공급 되었을때만 사용합니다.

Preferred:

var diameter: Double {
  return radius * 2
}

Not Preferred:

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

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.

> final을 사용하면 때로는 귀하의 의도를 분명히 할 수 있으며 비용을 감당할 가치는 있습니다.

// 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
  }
}

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

> 한줄에 짧은 함수 선언을 유지하세요.

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:

> 긴 함수의 경우 각 매개 변수를 새행에 넣고 후속 행에 추가 들여쓰기를 넣어주세요.

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.

> 파라미터에 Void를 사용하지말고 () 를 사용하세요. 클로저나 함수의 output에는 () 대신 Void를 사용하세요.

Preferred:

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

typealias CompletionHandler = (result) -> Void

Not Preferred:

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

typealias CompletionHandler = (result) -> ()

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

> 함수를 호출할때, 함수 선언의 스타일을 반영하세요.

let success = reticulateSplines(splines)

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

> 만약 함수가 길다면 각 매개변수를 줄바꿈 해줍니다.

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

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.

> 매개변수 마지막에 하나의 클로저가 있다면 trailing closure syntax를 사용하세요.

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:

> 컨텍스트가 명확한 단일 표현식 클로저의 경우는 암시적 리턴을 사용하세요.

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:

> 후행 클로저를 사용하는 체인화 된 메소드는 문맥에서 명확하고 쉽게 읽을 수 있어야 합니다.

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}

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.

> 가능한 Swift의 기본 타입 및 표현식을 사용하세요.

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 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.

> 상수는 let 키워드를, 변수는 var 키워드로 정의 되어 있습니다. 만약 값이 변하지 않는다면 var 대신 let을 항상 사용하세요.

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 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.

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

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
}

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.

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]()

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.

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>

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

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.

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)
}

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()
}

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
}

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

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 conditions and the code is indented one additional level, 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")
}

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.

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 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")

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."

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.

Where an Xcode project is involved, the organization should be set to Ray Wenderlich and the Bundle Identifier set to com.raywenderlich.TutorialName where TutorialName is the name of the tutorial project.

The following copyright statement should be included at the top of every source file:

/// Copyright (c) 2019 Razeware LLC
///
/// Permission is hereby granted, free of charge, to any person obtaining a copy
/// of this software and associated documentation files (the "Software"), to deal
/// in the Software without restriction, including without limitation the rights
/// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
/// copies of the Software, and to permit persons to whom the Software is
/// furnished to do so, subject to the following conditions:
///
/// The above copyright notice and this permission notice shall be included in
/// all copies or substantial portions of the Software.
///
/// Notwithstanding the foregoing, you may not use, copy, modify, merge, publish,
/// distribute, sublicense, create a derivative work, and/or sell copies of the
/// Software in any work that is designed, intended, or marketed for pedagogical or
/// instructional purposes related to programming, coding, application development,
/// or information technology.  Permission for such use, copying, modification,
/// merger, publication, distribution, sublicensing, creation of derivative works,
/// or sale is expressly withheld.
///
/// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
/// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
/// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
/// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
/// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
/// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
/// THE SOFTWARE.

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:

:]

Not Preferred:

:)

• The Swift API Design Guidelines
• The Swift Programming Language
• Using Swift with Cocoa and Objective-C
• Swift Standard Library Reference