Classes, structures, and enumerations can all define instance methods；
Classes, structures, and enumerations can also define type methods。 In Objective-C, classes are the only types that can define methods，In Swift, you can choose whether to define a class, structure, or enumeration, and still have the flexibility to define methods on the type you create.
Instance Methods 实例方法
Class
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
Struct
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"
Modifying Value Types from Within Instance Methods 从实例方法中修改值类型
struct Point{
var x=0.0,y=0.0
mutating func moveBy(x deltaX:Double,y deltaY:Double) { //mutating关键字被添加到其定义，以使其能够修改其属性。
x +=deltaX
y +=deltaY
}
}
var somePoint=Point(x:1.0,y:1.0)
somePoint.moveBy(x:2.0,y:3.0) // 改变实例属性
print("The point is now at (\(somePoint.x),\(somePoint.y))")
// Prints "The point is now at (3.0, 4.0)"
let fixedPoint=Point(x:3.0,y:3.0)
fixedPoint.moveBy(x:2.0,y:3.0)
// this will report an error 因为fixedPoint是个常量无法改变其实例属性
Assigning to self Within a Mutating Method 重新改变自己
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) //实例对象调用实例方法改变对象本身
}
}
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 类方法
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) { //类方法 操作的是类属性highestUnlockedLevel
if level>highestUnlockedLevel {
highestUnlockedLevel=level
}
}
static func isUnlocked( _ level:Int) -> Bool{ // 类方法 操作的是类属性highestUnlockedLevel
return level <= highestUnlockedLevel
}
@discardableResult //忽略返回值的代码不一定是错误
mutating func advance(to level:Int) ->Bool{ // 可修改的实例方法 操作的是实例属性
if LevelTracker.isUnlocked(level) { // 调用类方法
currentLevel=level
return true
}else{
return false
}
}
}
class Player{
var tracker = LevelTracker()
let playerName:String
func complete(level:Int) {
LevelTracker.unlock(level+1) // 调用类方法
tracker.advance(to:level+1) // 调用实例方法
}
init(name:String) { //属性构造器
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"
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"