Methods (study notes)
Environment Xcode 11.0 beta4 swift 5.1
- method
- Structures, enumerations, a method class may be defined (instance method, type method)
- Examples of the method (Instance Methods)
Examples of the method can only be called instance can not be used alone
class Counter { var count = 0 func increment() { count += 1 } func increment(by amount: Int) { count += amount } func reset() { count = 0 } } let counter = Counter() // the initial counter value is 0 counter.increment() // the counter's value is now 1 counter.increment(by: 5) // the counter's value is now 6 counter.reset() // the counter's value is now 0
self
Attribute, for each instance of the implicit type has the properties// 上面的increment()可写成如下形式 func increment() { self.count += 1 } // 如果方法的参数与实例相同时,就要显示的调用 self struct Point { var x = 0.0, y = 0.0 func isToTheRightOf(x: Double) -> Bool { return self.x > x } } let somePoint = Point(x: 4.0, y: 5.0) if somePoint.isToTheRightOf(x: 1.0) { print("This point is to the right of the line where x == 1.0") } // Prints "This point is to the right of the line where x == 1.0"
Within an instance method modifies the value of type using
mutating
the keyword modified the method of assigning a new instance to the hiddenself
, the end of this new method will replace the instance instance already exists// 枚举、结构体都是值类型 struct Point { var x = 0.0, y = 0.0 mutating func moveBy(x deltaX: Double, y deltaY: Double) { x += deltaX y += deltaY } } var somePoint = Point(x: 1.0, y: 1.0) somePoint.moveBy(x: 2.0, y: 3.0) print("The point is now at (\(somePoint.x), \(somePoint.y))") // Prints "The point is now at (3.0, 4.0)" // 不能用常量来调用 `mutating` 修饰的方法,因为常量不可修改 let fixedPoint = Point(x: 3.0, y: 3.0) fixedPoint.moveBy(x: 2.0, y: 3.0) // this will report an error
Method for the variable
self
assignment (Assigning to self Within a Mutating Method )// 上面的Point可以写成下面的形式 struct Point { var x = 0.0, y = 0.0 mutating func moveBy(x deltaX: Double, y deltaY: Double) { self = Point(x: x + deltaX, y: y + deltaY) } } // 枚举的可变方法 enum TriStateSwitch { case off, low, high mutating func next() { switch self { case .off: self = .low case .low: self = .high case .high: self = .off } } } var ovenLight = TriStateSwitch.low ovenLight.next() // ovenLight is now equal to .high ovenLight.next() // ovenLight is now equal to .off
- Type methods
In the
func
front keywordstatic
orclass
(subclass can only be used in a class, and may override the parent implementation) is modified, the type of processself
point type itselfclass SomeClass { class func someTypeMethod() { // type method implementation goes here } } SomeClass.someTypeMethod()
struct LevelTracker { static var highestUnlockedLevel = 1 var currentLevel = 1 // static func unlock(_ level: Int) { if level > highestUnlockedLevel { highestUnlockedLevel = level } } // static func isUnlocked(_ level: Int) -> Bool { return level <= highestUnlockedLevel } // @discardableResult mutating func advance(to level: Int) -> Bool { if LevelTracker.isUnlocked(level) { currentLevel = level return true } else { return false } } } class Player { var tracker = LevelTracker() let playerName: String func complete(level: Int) { LevelTracker.unlock(level + 1) tracker.advance(to: level + 1) } init(name: String) { playerName = name } } var player = Player(name: "Argyrios") player.complete(level: 1) print("highest unlocked level is now \(LevelTracker.highestUnlockedLevel)") // Prints "highest unlocked level is now 2" // 创建一个新的player player = Player(name: "Beto") if player.tracker.advance(to: 6) { print("player is now on level 6") } else { print("level 6 has not yet been unlocked") } // Prints "level 6 has not yet been unlocked"