Introduction to Kotlin (for Java Developers) - Cool Features - 14. Infix functions (no period and brackets).kt

/**
 * MUST:
 * - be an extension function OR a member function
 * - have a single parameter with no default value
 * - have the "infix" keyword
 */
infix fun Int.plus(that: Int) = this + that
// infix fun doStuff1() = println("blablabla") // COMPILER ERROR
// infix fun Int.doStuff2(a: Int, b: String) = println("blablabla") // COMPILER ERROR
// infix fun doStuff3(a: Int) = println("blablabla") // COMPILER ERROR
// infix fun Int.doStuff4(a: Int = 5) = println("blablabla") // COMPILER ERROR

class InfixExample {

    // Makes code closer to natural language
    fun test() {
        val sum = 1 plus 1
        println(sum plus 20)

        // "until" and "downTo" are also infix functions
        for (i in 1 until 4) println(i)
        for (i in 4 downTo 1) println(i)
    }

}