Swift中用到extension的一些基本的扩展功能讲解

extension SomeType {
   // new functionality can be added here
}
现有类型也可以用扩展加入使它作为一个协议标准和其语法类似于类或结构。

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

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 addition = 3.add
println("Addition is \(addition)")
   
let subtraction = 120.sub
println("Subtraction is \(subtraction)")
   
let multiplication = 39.mul
println("Multiplication is \(multiplication)")
   
let division = 55.div
println("Division is \(division)")

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

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

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()
println ("Inside mult block \(calc.a.num1, calc.a.num2)")
println("Inside mult block \(calc.b.no1, calc.b.no2)")
  
let memcalc = mult(a: sum(num1: 300, num2: 500),b: diff(no1: 300, no2: 100))
 
println("Inside mult block \(memcalc.a.num1, memcalc.a.num2)")
println("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)
println("Inside Sum Block:\( a.num1, a.num2)")
  
  
let b = diff(no1: 200, no2: 100)
println("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)

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

4.topics({
   println("Inside Extensions Block")      
})   
   
3.topics({
   println("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

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

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

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

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

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

extension Int {
   subscript(var multtable: Int) -> Int {
      var no1 = 1
      while multtable > 0 {
         no1 *= 10
         --multtable
      }
      return (self / no1) % 10
   }
}
   
println(12[0])
println(7869[1])
println(786543[2])

2
6
5

 extension Int {
   enum calc
   {
      case add
      case sub
      case mult
      case div
      case anything
   }

   var print: calc {
      switch self
      {
         case 0:
            return .add
         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 {
         case .add:
            println(" 10 ")
          case .sub:
            println(" 20 ")
         case .mult:
         println(" 30 ")
         case .div:
         println(" 40 ")
         default:
         println(" 50 ")

      }
   }
}

result([0, 1, 2, 3, 4, 7])

10 
20 
30 
40 
50 
50