Swift 学习第一节

@(Swift 深入学习小记)

1. if 语句缺省值的使用。

var str: String? = "string"
if let s = str {
    print("print \(s)")
}

2. switch 支持任意类型的数据以及各种比较操作（不仅仅是整数）

let str = "red pepper"
switch str {
    case "celery":
    print("add some raisins and make ants on a log.")
    case let x where x.hasSuffix("pepper"):
    print("It is a spicy \(x)")
}

3. for 循环来遍历字典

let dic = ["name":"chuck", "age":"10", "nickname":"zhangsan"]
for (kind, numbers) in dic {
    for number in numbers {
        if number == "10" {
            print("is age number == 10")
        }
    }
}

4. while 知道代码满足条件

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

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

5. 函数与闭包

   • 函数可以用元祖来当返回值

    func array(arr: [Int]) -> (min: Int, max: Int, sum: Int) {
        var min = arr[0]
        var max = arr[0]
        var sum = 0
        for a in arr {
            if a > max {
                max = a
            } else if a < min {
                min = a
            }
            sum += a
        }
        return (min, max, sum)
    }

- 函数可以带可变参数

    func sum(numbers: Int...) -> Int {
        var sum = 0
        for num in numbers {
            sum += num
        }
        return sum
    }

- 函数还可以嵌套
- 函数也可以当另一个函数的参数传入

6. 闭包

    // 闭包可以直接使用，在确定的情况下，可以省略参数和返回值类型
    let numbers = [1,0,2,3,4]
    let sum = numbers.map({ (num:Int) -> Int in
        let resutl = 3 * num
        return resutl
    })

    let sum = numbers.map({number in number * 3})

    // 在最后一个参数是一个闭包的时候，可以直接用花括号取消小括号
    
    let sor = numbers.sorted {$0 > $1}      

7. Switch 支持 Where 进一步条件判断(还可以添加复合分支)

let yetAnotherPoint = (1, -1)
switch yetAnotherPoint {
case let (x, y) where x == y:
    print("(\(x), \(y)) is on the line x == y")
case let (x, y) where x == -y:
    print("(\(x), \(y)) is on the line x == -y")
case let (x, y):
    print("(\(x), \(y)) is just some arbitrary point")
}
// 打印 "(1, -1) is on the line x == -y"

8. fallthrough 可以用来贯穿switch

9. 泛型

   • 泛型函数
   • 泛型类型