Varargs allow you to pass any number of arguments by separating them with commas. The vararg modifier turns a parameter into a vararg. This allows calling printAll with any number of string arguments. Thanks to named parameters, you can even add another parameter of the same type after the vararg. This wouldn’t be allowed in Java because there’s no way to pass a value. Using named parameters, you can set a value to prefix separately from the vararg. At runtime, a vararg is just an array. To pass it along into a vararg parameter, use the special spread operator *…

Certain functions can be “upgraded” to operators, allowing their calls with the corresponding operator symbol. This takes the infix function from above one step further using the operator modifier. The operator symbol for times() is * so that you can call the function using 2 * “Bye”. An operator function allows easy range access on strings. The get() operator enables bracket-access syntax. operator fun Int.times(str: String) = str.repeat(this) println(2 * "Bye ") operator fun String.get(range: IntRange) = substring(range) val str = "Always forgive your enemies; nothing annoys them so much." println(str[0..14])  

Member functions and extensions with a single parameter can be turned into infix functions. Defines an infix extension function on Int. Calls the infix function. Creates a Pair by calling the infix function to from the standard library. Here’s your own implementation of to creatively called onto. Infix notation also works on members functions (methods). The containing class becomes the first parameter. Note that the example uses local functions (functions nested within another function). fun main() { infix fun Int.times(str: String) = str.repeat(this) println(2 times "Bye ") val pair = "Ferrari" to "Katrina" println(pair) infix fun String.onto(other: String) = Pair(this,…

A simple function that takes a parameter of type String and returns Unit (i.e., no return value). A function that takes a second optional parameter with default value Info. The return type is omitted, meaning that it’s actually Unit. A function that returns an integer. A single-expression function that returns an integer (inferred). Calls the first function with the argument Hello. Calls the function with two parameters, passing values for both of them. Calls the same function omitting the second one. The default value Info is used. Calls the same function using named argument and changing the order of the arguments. Prints…

fun main() { println("Hello, World!") } An entry point to a Kotlin application is the main function. In Kotlin 1.3, you can declare main without any parameters. The return type is not specified, which means that the function returns nothing. println writes a line to the standard output. It is imported implicitly. Also note that semicolons are optional. In Kotlin versions earlier than 1.3, the main function must have a parameter of type Array<String>. fun main(args: Array<String>) { println("Hello, World!") }