Kotlin: function

function default value

參數可以宣告 default 值

 fun connectToDb(hostname: String = "localhost",

                username: String = "mysql",

                password:String = "secret") {

}

這樣不用特別定義多個 functions 給不同參數的狀況. 

而可以省略呼叫用 default 值的參數, 如下:

connectToDb("mycomputer","root")

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Extension Functions

class Greeter {
    fun hello(msg: String) = "Hello, $msg"
    fun hi(msg: String) = "Hi, $msg"
    fun terminatorify(msg: String) = "$msg, I'll be back"
}

fun main(args: Array<String>) {
    val name = "Simpson"

    val g = Greeter();
    println(g.hello(name))
    println(g.hi(name))
    println(g.terminatorify(name))
}

執行結果：

Hello, Simpson

Hi, Simpson

Simpson, I'll be back

----

infix

class Person(val name : String) {
    fun say(message: String) = println("$name is saying $message")
}

fun main(args: Array<String>) {
    val Simpson = Person("Simpson")
    Simpson.say("Hello World!")
}

Simpson is saying Hello World!

像這函式只有一個參數, 可以改用 infix

class Person(val name : String) {
    infix fun say(message: String) = println("$name is saying $message")
}

這樣可以用底下這方式呼叫：

fun main(args: Array<String>) {
    val Simpson = Person("Simpson")
    Simpson say "Hello World!"
}

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operator overloading