控制流 control flow

let somePoint = (1, 1)
switch somePoint {
case (0, 0):
    println("(0, 0) is at the origin")
case (_, 0)://使用下划线(underscore)代表任何可能的值
    println("(\(somePoint.0), 0) is on the x-axis")
case (0, _):
    println("(0, \(somePoint.1)) is on the y-axis")
case (-2...2, -2...2):
    println("(\(somePoint.0), \(somePoint.1)) is inside the box")
default:
    println("(\(somePoint.0), \(somePoint.1)) is outside of the box")

//prints "(1, 1) is inside the box"

let anotherPoint = (2, 0)
switch anotherPoint {
case (let x, 0):
　　println("on the x-axis with an x value of \(x)")
case (0, let y):
　　println("on the y-axis with a y value of \(y)")
case let (x, y):
　　println("somewhere else at (\(x), \(y))")
}

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