(本文所有代码样例全部来自Swift2.0官方文档)

1. Swift类型间不会隐式转换，必须要显式转换。将值转换成字符串除了使用String()显式转换外，还有中简单的方法,如下:

   let apples = 3
   let oranges = 5
   
   let appleSummary = "I have \(apples) apples."
   
   let fruitSummary = "I have \(apples + oranges)  pieces of fruit."
   

   输出:

   "I have 3 apples"
   "I have 8 pieces of fruit"
   

2. Swift声明数组或者字典可以声明指定类型

   let emptyArray = [String]()
   let emptyDictionary = [String: Float]()
   

3. if语句中，条件必须是一个布尔表达式,如下:

    if score > 50 {
       teamScore += 3
   
   } else {
   
          teamScore += 1
   
   }
   

   if 1 {} 这样代码会报错，但是if true{}这样的代码是可 以的。

4. Switch 支持任意类型的数据以及各种比较，不仅仅限于整数以及判断是否相等,而且Switch匹配到相应的子句之后就会推出整个Switch,不需要给每个Switch子句写上break了。

   let vegetable = "red pepper"
   switch vegetable {
   
   case "celery":
   
       print("Add some raisins and make ants on a  log.")
   
   case "cucumber", "watercress":
   
       print("That would make a good tea sandwich.")
   
   case let x where x.hasSuffix("pepper"):
   
       print("Is it a spicy \(x)?")
   
   default:
   
       print("Everything tastes good in soup.")
   
   }
   

   Swift 子句中必须要遍历所有可能，否则会报错
   上述代码中的lex表达式将匹配等式的值赋给变量x

5. do{}while()被repeat{}while()取代

   var m = 2
   repeat {
   
       m = m * 2
   
   } while m < 100
   
   print(m)
   

6. 循环有更简便的写法,0..<4表示遍历0到4(不包含4，包含4用0...4),传统写法也是支持的。

   var firstForLoop = 0
   for i in 0..<4 {
   
       firstForLoop += i
   
   }
   
   print(firstForLoop)
   
   var firstForLoop = 0
   
   for i in 0...4 {
   
       firstForLoop += i
   
   }
   
   print(firstForLoop)
   

7. 函数可以传入可变的参数，参数在函数内表现为数组形式:

   func sumOf(numbers: Int...) -> Int {
   var sum = 0
   
   for number in numbers {
   
       sum += number
   
   }
   
   return sum
   
   }
   
   sumOf()
   
   sumOf(42, 597, 12)
   

8. 函数可以作为另一个函数的返回值，类似于OC中的block

   func makeIncrementer() -> (Int -> Int) {
   func addOne(number: Int) -> Int {
   
       return 1 + number
   
   }
   
   return addOne
   
   }
   
   var increment = makeIncrementer()
   
   increment(7)
   

   同理，函数也可以当做参数传入函数,

   func hasAnyMatches(list: [Int], condition: Int ->   Bool) -> Bool {
   for item in list {
   
       if condition(item) {
   
           return true
   
       }
   
   }
   
   return false
   
   }
   
   func lessThanTen(number: Int) -> Bool {
   
       return number < 10
   
   }
   
   var numbers = [20, 19, 7, 12]
   
   hasAnyMatches(numbers, condition: lessThanTen)
   

9. 子类中，如果需要重写父类的方法，需要使用override标记

   class NamedShape {
   var numberOfSides: Int = 0
   
   var name: String
   
   init(name: String) {
   
       self.name = name
   
   }
   
   func simpleDescription() -> String {
   
           return "A shape with \(numberOfSides) sides."
   
     }
   
   }
   
   class Square: NamedShape {
   
   var sideLength: Double
   
   init(sideLength: Double, name: String) {
   
       self.sideLength = sideLength
   
       super.init(name: name)
   
       numberOfSides = 4
   
   }
   
   func area() ->  Double {
   
       return sideLength * sideLength
   
   }
   
   override func simpleDescription() -> String {
   
           return "A square with sides of length \(sideLength)."
   
       }
   
   }
   
   let test = Square(sideLength: 5.2, name: "my test   square")
   
   test.area()
   
   test.simpleDescription()