如何在静态编程语言中实现开关案例语句

Question

如何在静态编程语言中实现等效于遵循Java开关语句代码？

switch (5) {
    case 1:
    // Do code
    break;
    case 2:
    // Do code
    break;
    case 3:
    // Do code
    break;
}

Answer 1

Kotlin的开关外壳非常灵活

when(x){

    2 -> println("This is 2")

    3,4,5,6,7,8 -> println("When x is any number from 3,4,5,6,7,8")

    in 9..15 -> println("When x is something from 9 to 15")

    //if you want to perform some action
    in 20..25 -> {
                 val action = "Perform some action"
                 println(action)
    }

    else -> println("When x does not belong to any of the above case")

}

Answer 2

Java中的开关在Kotlin中有效地使用。但是，语法是不同的。

when(field){
    condition -> println("Single call");
    conditionalCall(field) -> {
        print("Blocks");
        println(" take multiple lines");
    }
    else -> {
        println("default");
    }
}

这里有一个不同用途的例子：

// This is used in the example; this could obviously be any enum. 
enum class SomeEnum{
    A, B, C
}
fun something(x: String, y: Int, z: SomeEnum) : Int{
    when(x){
        "something" -> {
            println("You get the idea")
        }
        else -> {
            println("`else` in Kotlin`when` blocks are `default` in Java `switch` blocks")
        }
    }

    when(y){
        1 -> println("This works with pretty much anything too")
        2 -> println("When blocks don't technically need the variable either.")
    }

    when {
        x.equals("something", true) -> println("These can also be used as shorter if-statements")
        x.equals("else", true) -> println("These call `equals` by default")
    }

    println("And, like with other blocks, you can add `return` in front to make it return values when conditions are met. ")
    return when(z){
        SomeEnum.A -> 0
        SomeEnum.B -> 1
        SomeEnum.C -> 2
    }
}

其中大多数编译为开关，除了{...}时的，它编译为一系列if语句。

但对于大多数用途，如果您在（字段）时使用，它将编译为开关（字段）。

然而，我想指出的是，带有大量分支的开关（5）只是浪费时间。5永远是5。如果使用开关、If语句或任何其他逻辑运算符，则应使用变量。我不确定这段代码是一个随机的例子，还是实际的代码。我要指出这一点，以防是后者。

Answer 3

你可以这样做：

when (x) {
    1 -> print("x == 1")
    2 -> print("x == 2")
    else -> { // Note the block
        print("x is neither 1 nor 2")
    }
}

摘自官方帮助