類和結構體

蘋果官方文檔 Classes and Structures

蘋果官方文檔翻譯 類和結構體

類與結構體的對比

定義語法

  class SomeClass {
      // class definition goes here
  }  
  struct SomeStructure {
      // structure definition goes here
  }

一個實際的代碼例子如下：

struct Resolution {
    var width = 0
    var height = 0
}
class VideoMode {
    var resolution = Resolution()
    var interlaced
}

類與結構體實例

let someResolution = Resolution()
let someVideoMode = VideoMode()

訪問屬性

print("The width of someResolution is \(someResolution.width)")
// prints "The width of someResolution is 0"

print("The width of someVideoMode is \(someVideoMode.resolution.width)")
// prints "The width of someVideoMode is 0"

someVideoMode.resolution.width = 1280
print("The width of someVideoMode is now \(someVideoMode.resolution.width)")

結構體類型的成員初始化器

let vga = Resolution(width: 640, height: 480)

但是，類實例不會接收預設的成員初始化器。

結構體和枚舉是值類型

值類型是一種當它被指定到常量或者變數，或者被傳遞給函數時會被拷貝的類型。

let hd = Resolution(width: 1920, height: 1080)
var cinema = hd
cinema.width = 2048
println("cinema is now \(cinema.width) pixels wide")
//println "cinema is now 2048 pixels wide"
print("hd is still \(hd.width) pixels wide")
// prints "hd is still 1920 pixels wide"

enum CompassPoint {
    case North, South, East, West
}
var currentDirection = CompassPoint.West
let rememberedDirection = currentDirection
currentDirection = .East
if rememberedDirection == .West {
    print("The remembered direction is still .West")
}
// prints "The remembered direction is still .West"

類是引用類型

let tenEighty = VideoMode()
tenEighty.resolution = hd
tenEighty.interlaced = true
tenEighty.name = "1080i"
tenEighty.frameRate = 25.0

let alsoTenEighty = tenEighty
alsoTenEighty.frameRate = 30.0

print("The frameRate property of tenEighty is now \(tenEighty.frameRate)")
// prints "The frameRate property of tenEighty is now 30.0"

特征運算符

找出兩個常量或者變數是否引用自同一個類實例非常有用，為了允許這樣，Swift提供了兩個特點運算符：

相同於 ( ===)
不相同於( !==)

if tenEighty === alsoTenEighty {
    print("tenEighty and alsoTenEighty refer to the same VideoMode instance.")
}
// prints "tenEighty and alsoTenEighty refer to the same VideoMode instance."

類和結構體之間的選擇

字元串，數組和字典的賦值與拷貝行為

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