Swift从入门到精通第八篇 - 方法 初识
2024-09-01 06:32:47
方法（学习笔记）
环境Xcode 11.0 beta4 swift 5.1
方法
- 结构体、枚举、类都可以定义方法（实例方法、类型方法）
实例方法（Instance Methods）
实例方法只能用实例来调用，不能单独使用
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属性，每个类型的实例都有的隐式的属性// 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"
实例方法内修改值类型用
mutating关键字修饰，该方法分配一个新的实例给隐藏的self,方法结束这个新的实例将会替换掉已经存在的实例// 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
可变方法内给
self赋值（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
类型方法
在
func前用关键字static或者class(只能在类中使用，且子类可以重写父类的实现)修饰，类型方法中self指向类型本身class 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"
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