Kotlin functions

1、function member

val onClick: () -> Unit = …

2、nullable function

val intFunc: ((Int, Int) -> Int)? = null

3、function type

typealias ClickHandler = (Button, ClickEvent) -> Unit

4、anonymous function

fun(s: String): Int { return s.toIntOrNull() ?: 0 }

5、lamda expression

val reminderFunc = { index: Int -> index % 2 }

6、callable reference

member function ::toString, String::toInt
member property List::size
constructor ::someConstructorFuncName

7、class function

class IntTransformer: (Int) -> Int {
    override operator fun invoke(x: Int): Int = TODO()
}
val intFunction: (Int) -> Int = IntTransformer()

8、instance function

val repeatFun: String.(Int) -> String = { times ->
    this.repeat(times)
}
val twoParameters: (String, Int) -> String = repeatFun
val s1 = repeatFun(“str”, 2)
val s2 = “str”.repeatFun(2)

9、builder function

class HTML {
    fun body() { … }
}

fun html(init: HTML.() -> Unit): HTML {
    val html = HTML() // create the receiver object
    html.init() // pass the receiver object to the lambda
    return html
}

val obj = html { // lambda with receiver begins here
    body() // calling a method on the receiver object
}

10、infix function

class HTML {
    infix fun escape(escaper: (String) -> String){…}
}
val obj = HTML() escape { s: String -> “switch s case xxx”}