Swift Switch 语句

前言

• Swift switch 语句中，默认语法是必须要添加 default 语句。
• Swift Switch 语句中， break 是可以省略不写的，默认执行完当前 case 下的内容后，直接返回了，即使后续还有可满足的条件。

基础用法

let someChar: Character = "z"
switch someChar {
case "a":
    print("this is a ")
case "b":
    print("this is b")
case "z":
    print("this is z")
default:
    print("this is else ")
}

输出结果
this is z

复合匹配

复合匹配就是 同一个 Case 下的多个条件

这里的多个条件就是 ，可能是 a，或者 b ，任何一个条件匹配了，那么就被认为当前条件满足。

let someChar: Character = "Z"
switch someChar {
case "a":
    print("this is a ")
case "z","Z":
    print("this is z")
default:
    print("this is else ")
}

输出结果
this is z

区间匹配

被判断的值要满足 case 语句的区间条件

let count = 20
var resultValue = ""
switch count {
case 0:
    resultValue = "none"
case 1..<12:
    resultValue = "a few"
case 12..<100:
    resultValue = "dozens of"
case 100..<1000:
    resultValue = "hundreds of"
default:
    resultValue = "many"
}
print(resultValue)

输出结果
dozens of

元组匹配

let somePoint = (1,1)

switch somePoint {
case (0, 0):
    print("point at origin")
case (_, 0):    //下划线表示可以是任意值，这里的条件是只需要满足第二个值0
    print("point at x-axis")
case (0, _):    // 下划线表示可以是任意值，这里的条件是只需要满足第一个是0
    print("point at y-axis")
case (-2...2, -2...2):
    print("point is box")
default:
    print("point at other place")
}

输出结果
point is box

值绑定

let somePoint = (1,0)

switch somePoint {
case (0, 0):
    print("point at origin")
case (let x, 0):    // 当前条件只需要满足第二个值是0， 并且可以引用 x 来获取第一位的值，
    print("point at x-axis , distance is \(x)")
case (0, let y):     // 当前条件只需要满足第一个值是0， 并且可以引用 x 来获取第二位的值，
    print("point at y-axis, distance is \(y)")
case (-2...2, -2...2):
    print("point is box")
default:
    print("point at other place")
}

输出结果
point at x-axis , distance is 1

where 语句

switch case 可以使用 where 分句来检查是否符合特定的约束

let point = (1,2)
switch point {
case (0, 0):
    print("---- 0, 0")
case (let x, let y) where y == 2:
    print("second value = 2")
default:
    print("other value")
}

输出结果
second value = 2

复合匹配-值绑定

let value = (9, 0)
switch value {
case (let v, 0), (0, let v):
    print("value is \(v)")
default:
    print("not value")
}