Swift 笔记（四）

我的主力博客：半亩方塘

Making Decisions

1、Consider this code:

let number = 10
switch (number) {
case let x where x % 2 == 0:
    print("Even")
default:
    print("Odd")
}  

This will print the following:

Even

This switch statement uses thelet-wheresyntax,meaning the case will match only when a certain condition is true. In this example,you've designed the case to match if the value is even-that is,if the value modulo 2 equals 0.

The method by which you can match values based on conditions is known aspattern matching.

2、Another way you can useswitchstatements to great effect is as follows:

let coordinates: (x: Int,y: Int,z: Int) = (3,2,5)
switch (coordinates) {
case (0,0):
    print("Origin")
case (_,0):
    print("On the x-axis.")
case (0,_,0):
    print("On the y-axis.")
case (0,_):
    print("On the z-axis.") 
default:
    print("Somewhere in space")
}  

You're using the underscore to mean that you don't care about the value. If you don't want to ignore the value,then you can use it in yourswitchstatement,like this:

let coordinates: (x: Int,0):
    print("Origin")
case (let x,0):
    print("On the x-axis at x = (x)")
case (0,let y,0):
    print("On the y-axis at y = (y)")
case (0,let z):
    print("On the z-axis at z = (z)")
case (let x,let z):
    print("Somewhere in space at x = (x),y = (y),z = (z)")  
}  

let coordinates: (x: Int,5)
switch(coordinates) {
case (let x,_) where y == x:
    print("Along the y = x line.")
case (let x,_) where y == x * x:
    print("Along the y = x^2 line.")
default:
    break
}

（编辑：李大同）

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