Swift Coding Style

本篇文章介绍如何用最规范的形式书写Swift。作者力求团队内部合作的时候代码风格统一，减少模糊代码，尽量美观，保持最佳实践。

基本

• 缩进使用Tab而不是Space
• 文件结尾添加一行空行
• 行尾不建议使用『;』
• 正括号不换行，与之前的字母空一个空格

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

• 『:』，『,』左边不空格，右边空一个
• 『[』，『]』，『(』，『)』内部不建议空格

let a: [String] = ["1", "b"]

• 单行注释『//』后面空一格
• 使用『// MARK:』，『// TODO:』，『// FIXME:』来注释

// MARK: 添加键盘方法
// MARK: - UITableViewDelegate  (带横线版本会被编译成水平分割线)
// TODO: zjs, 多线程保护
// FIXME: 缺少类型判断

• 不使用namespace前缀(NSXXX，RRDXXX)，swift会根据framework自动添加namespace

进阶

尽量使用let代替var

Preferred:

let tempValue = "tempValue"

Not Preferred:

var temp ＝ "tempValue"

推荐使用类型推断

Preferred:

let message = "Click the button"
let currentBounds = computeViewBounds()
var names = [String]()
let maximumWidth: CGFloat = 106.5

Not Preferred:

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

推荐使用便捷语法

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>

尽量使用String代替NSString

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

全局变量命名使用UpperCamelCase

Preferred:

public let MaximumWidgetCount = 100

Not Preferred:

public let maximumWidgetCount = 100
public let MAX_WIDGET_COUNT = 100

枚举类型命名使用UpperCamelCase

enum Shape {
  case Rectangle
  case Square
  case Triangle
  case Circle
}

尽早的使用guard判断退出

Preferred:

func login(name: String?, password: String?) {
 guard let name = name, password = password else {return}
 // ...do something
}

Not Preferred:

func login(name: String?, password: String?) {
 // ...do something
 if let name = name, password = password {
  // ...do something
 } else {return}
}

尽量使用as?代替as!

Preferred:

func parse(dict: [String: AnyObject]) {  
 guard let data = dict["data"] as? [String: AnyObject] else {return}
 // ...do something
}

Not Preferred:

func parse(dict: [String: AnyObject]) {  
 let data = dict["data"] as! [String: AnyObject]
 // ...do something
}

尽量使用Optional Chaining

Preferred:

func pop(viewController: UIViewController?) {  
 viewController?.navigationController?.popViewControllerAnimated(true)
}

Not Preferred:

func pop(viewController: UIViewController?) {  
 if let viewController = viewController {
  // ...do something
 }
}

read-only properties 推荐使用隐式的get方法

Preferred:

var myGreatProperty: Int {
    return 4
}

Not Preferred:

var myGreatProperty: Int {
 get {
  return 4
 }
}

对外使用的类显示标注public和private

public var whoopsGlobalState: Int
private func doTheThings(things: [Thing]) {}
private(set) var offset:Int = 0;

访问类变量时不省略self

Preferred:

class History {
    var events: [Event] = [Event]()
    func rewrite() {
        self.events = []
    }
}

Not Preferred:

class History {
    var events: [Event]
    func rewrite() {
        events = []
    }
}

括号表达式

Preferred:

 UIView.animateWithDuration(1.0) {
  self.myView.alpha = 0
}

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

Not Preferred:

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

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

Struct初始化

Preferred:

let bounds = CGRect(x: 40, y: 20, width: 120, height: 80)
let centerPoint = CGPoint(x: 96, y: 42)

Not Preferred:

let bounds = CGRectMake(40, 20, 120, 80)
let centerPoint = CGPointMake(96, 42)

不需要时尽量省略参数信息

Preferred:

struct Composite<T> {
    …
    func compose(other: Composite) -> Composite {
        return Composite(self, other)
    }
}

Not Preferred:

struct Composite<T> {
    …
    func compose(other: Composite<T>) -> Composite<T> {
        return Composite<T>(self, other)
    }
}

自定义运算符加空格

Preferred:

func <| (lhs: Int, rhs: Int) -> Int
func <|< <A>(lhs: A, rhs: A) -> A

Not Preferred:

func <|(lhs: Int, rhs: Int) -> Int
func <|<<A>(lhs: A, rhs: A) -> A

最佳实践

单例

class Account {
     static let sharedInstance = Account()
}

推荐使用extension实现protocol

Prefrerred:

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
}

尽量使用Struct而不是Class

使用Struct的情况:

• 赋值操作默认是copy操作
• 类型不属于AnyObject，属于Any
• 使用protocol+extension代替继承

protocol Vehicle {
    var numberOfWheels: Int { get }
}

func maximumTotalTirePressure(vehicle: Vehicle, pressurePerWheel: Float) -> Float {
    return pressurePerWheel * Float(vehicle.numberOfWheels)
}

struct Bicycle: Vehicle {
    let numberOfWheels = 2
}

struct Car: Vehicle {
    let numberOfWheels = 4
}

使用Class的情况:

• 赋值操作是指针复制操作
• 属于AnyObject
• 尽量使用protocol+extension代替继承

class默认添加final关键字

非基础类声明默认添加final关键字，如果后面有人需要继承再删除。

final class History {
    var events: [Event] = [Event]()
}

lazy写法

final class MyViewController: UIViewController {
    lazy var mainView: UIView = {
     let view = UIView()
     ... // do somethig
     return view
    }()
}

block weakself

func myFuction() {
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(2 * Double(NSEC_PER_SEC))), dispatch_get_main_queue(), {[weak self] () -> Void in
 guard let `self` = self else {return}
 self.backgroundColor = UIColor.blackColor()
}

Json解析

if let JSONObject = try NSJSONSerialization.JSONObjectWithData(data, options: .AllowFragments) as? [[String: AnyObject]],
    let username = (JSONObject[0]["user"] as? [String: AnyObject])?["name"] as? String {
        // There's our username
}

lazy sequence

lazy方式使用map,flatmap方法。
使用lazy方式每次访问都会进行计算。

let array = Array(1...1000)
let mapArray = array.lazy.map {$0 + 1}
print(mapArray[2]) // 访问时执行map运算

---

参考资料

https://github.com/raywenderlich/swift-style-guide
https://github.com/github/swift-style-guide
http://nshipster.cn/swift-documentation/
http://swift.gg/2016/03/25/being-lazy/