# Swift擴充套件

Swift擴充套件功能 -

• 新增計算屬性和計算型別屬性
• 定義範例和型別方法。
• 提供新的初始化程式。
• 定義下標
• 定義和使用新的巢狀型別
• 使現有型別符合協定

``````extension SomeType {
// new functionality can be added here
}
``````

``````extension SomeType: SomeProtocol, AnotherProtocol {
// protocol requirements is described here
}
``````

#### 計算屬性

``````extension Int {
var add: Int {return self + 100 }
var sub: Int { return self - 10 }
var mul: Int { return self * 10 }
var div: Int { return self / 5 }
}

let subtraction = 120.sub
print("Subtraction is \(subtraction)")

let multiplication = 39.mul
print("Multiplication is \(multiplication)")

let division = 55.div
print("Division is \(division)")

let mix = 30.add + 34.sub
print("Mixed Type is \(mix)")
``````

``````Addition is 103
Subtraction is 110
Multiplication is 390
Division is 11
Mixed Type is 154
``````

#### 初始化器

Swift 4提供通過擴充套件向現有型別新增新初始化程式的靈活性。 使用者可以新增自定義型別來擴充套件已定義的型別，也可以使用其他初始化選項。 擴充套件僅支援`init()`。 擴充套件不支援`deinit()`

``````struct sum {
var num1 = 100, num2 = 200
}

struct diff {
var no1 = 200, no2 = 100
}

struct mult {
var a = sum()
var b = diff()
}

let calc = mult()
print ("Inside mult block \(calc.a.num1, calc.a.num2)")
print("Inside mult block \(calc.b.no1, calc.b.no2)")

let memcalc = mult(a: sum(num1: 300, num2: 500),b: diff(no1: 300, no2: 100))
print("Inside mult block \(memcalc.a.num1, memcalc.a.num2)")
print("Inside mult block \(memcalc.b.no1, memcalc.b.no2)")

extension mult {
init(x: sum, y: diff) {
let X = x.num1 + x.num2
let Y = y.no1 + y.no2
}
}

let a = sum(num1: 100, num2: 200)
print("Inside Sum Block:\( a.num1, a.num2)")

let b = diff(no1: 200, no2: 100)
print("Inside Diff Block: \(b.no1, b.no2)")
``````

``````Inside mult block (100, 200)
Inside mult block (200, 100)
Inside mult block (300, 500)
Inside mult block (300, 100)
Inside Sum Block:(100, 200)
Inside Diff Block: (200, 100)
``````

#### 方法

``````extension Int {
func topics(summation: () -> ()) {
for _ in 0..<self {
summation()
}
}
}

4.topics(summation: {
print("Inside Extensions Block")
})

3.topics(summation: {
print("Inside Type Casting Block")
})
``````

``````Inside Extensions Block
Inside Extensions Block
Inside Extensions Block
Inside Extensions Block
Inside Type Casting Block
Inside Type Casting Block
Inside Type Casting Block
``````

`topics()`函式接受型別`(summation: () -> ())`的引數，以指示函式不接受任何引數，並且它不會返回任何值。 要多次呼叫該函式，初始化塊，並在初始化時對`topic()`的方法的呼叫。

#### 變異範例方法

``````extension Double {
mutating func square() {
let pi = 3.1415
self = pi * self * self
}
}

var Trial1 = 3.3
Trial1.square()
print("Area of circle is: \(Trial1)")

var Trial2 = 5.8
Trial2.square()
print("Area of circle is: \(Trial2)")

var Trial3 = 120.3
Trial3.square()
print("Area of circle is: \(Trial3)")
``````

``````Area of circle is: 34.210935
Area of circle is: 105.68006
Area of circle is: 45464.070735
``````

#### 下標

``````extension Int {
subscript(var multtable: Int) -> Int {
var no1 = 1
while multtable > 0 {
no1 *= 10
--multtable
}
return (self / no1) % 10
}
}

print(12[0])
print(7869[1])
print(786543[2])
``````

``````2
6
5
``````

#### 巢狀型別

``````extension Int {
enum calc {
case sub
case mult
case div
case anything
}
var print: calc {
switch self {
case 0:
case 1:
return .sub
case 2:
return .mult
case 3:
return .div
default:
return .anything
}
}
}

func result(numb: [Int]) {
for i in numb {
switch i.print {
print(" 10 ")
case .sub:
print(" 20 ")
case .mult:
print(" 30 ")
case .div:
print(" 40 ")
default:
print(" 50 ")
}
}
}
result(numb: [0, 1, 2, 3, 4, 7])
``````

``````10
20
30
40
50
50
``````