swift 中很好用的for循环语句for...in.它的实现原理是需要遵循SequenceType，且要县遵循GenreatorType 先看下面例子

//先定义一个实现了 GenreatorType Protocol的类型

`class TestList: SequenceType {

    private var testList:[Test]?
    init() {
        self.testList = [Test]()
    }
    
    func addTest(test:test){
        self.testList?.append(book)
    }
    
    typealias Generator = BookListGenerator
    
    func generate() -> Generator {
        
        return testListGenerator(bookList: self.bookList!)
        
    }

}`

class test {

    var name:String = ""
    init(name: String) {   
        self.name = name  
    }

}

class TestListGenerator : GeneratorType {}

    typealias Element = Book

    var currentIndex:Int = 0
    var testList:[Test]?
    
    init(testList: [Test]) {
        self.testList = bookList 
    }
    
    func next() -> Element? {
        
        guard let list = testList else { return  nil }
        
        if currentIndex < list.count {
            
            let element = list[currentIndex]
            currentIndex += 1
            return element
            
        }else {
            
            return nil
            
        }
    }

}

let testList = testList()

testList.addTest(Test(name: "Swift"))

testList.addTest(Test(name: "iOS" ))

for test in testList {

    print("\(test.name)")

}

• 看了上述的例子，大致可以自定义一个可以for...in的对象了
• 更惊喜的是我不还可以使用想数组的map\filter、reduce方法，这因为SquenceType已经扩展实现了它们