2014年8月1日 星期五

Swift Language Guide - SWITCH

Swift Language Guide - SWITCH

case MUST have body

let c = 20

switch c {
case 1:     <-- Error
case 20:
    println("20")
}

usage

let a = (1, 2)

switch a {
case let (x, y) where x == y:
    println("x = y")

case (let x, _) where x >= 0:
    println("x >= 0")
case (0, let y):
    println("x is zero")

case (_, 0):
    println("y is zero")

case (0...5, 1..<5):
    println("0 <= x <= 5 and 1<= y < 5")

default:
    println("nothing")
}

BREAK

break is not needed in switch-case, but you can use it if you want to do nothing.

let c = 20

switch c {
case 1:
    break
case 20:
    println("20")
default:
    break
}

FALLTHROUTH

fallthrough dose NOT check NEXT case condition and EXECUTE it's body.

let b = 10

switch b {
case 1...20:
    println("1 <= b <= 20")         <-- match and println
    fallthrough

case 11...20:
    println("11 <= b <= 20")        <-- println because of fallthrough

case 5...15:
    println("1 <= b <= 15")         <-- NOT be applied because of implicit break in case 11...20

default:
    println("nothing")              <-- NOT be applied because of implicit break in case 11...20
}

b = 10 matches case 1...20, fall in case 11...200 and implicit break after println("11 <= b <= 20"). So, case 5...15 and default will not be applied.

Limitation

fallthrough can NOT transfer control to a case label declares variables.

case (0...5, 1..<5):
    println("0 <= x <= 5 and 1<= y < 5")
    fallthrough     <-- Error

case (0, let y):    <-- value binding
    println("x is zero")
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