Kotlin Powerful when

Posted by On 6月 03, 2017 0 Comment

when

One of the interesting feature is when.
“when” clause is very powerful feature.
In other language, switch is similar feature.
But, when is more powerful.

switch like

fun useWhen(x : Any?) {
   when(x) {
       1 -> print("x == 1")
       2 -> print("x == 2")
       else -> {
           print("x is not 1 or 2")
       }
   }
}

x is Any type, we can use number, string, object etc…
It looks like switch, but in this case, we can use not only number.

Use with range

fun useWhen(x : Any?) {
    when(x) {
        in 1..10 -> print("1 to 10")
    }
}

Like if else

fun useWhen(obj: Any): String =
        when(obj) {
            1 -> "One"
            "Hello" -> "Greeting"
            is Long -> "Long"
            !is String -> "Not a String"
            else -> "Unknown"
        }

enum

Of course, we can use it with enum
Enums.kt

enum class ProtocolState { StateA, StateB, StateC}

Main.kt

fun useWhen2(protocol : ProtocolState) {
    when(protocol) {
        ProtocolState.StateA -> println("StateA")
        ProtocolState.StateB -> println("StateB")
        else -> println("StateC")

    }
}

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