[Kotlin] Infix Functions

In Kotlin, there is a method of defining functions called Infix functions, which is a syntax that was unimaginable while using Java as the primary language. Let's introduce this for those who are starting with Kotlin.

Member functions with a single parameter can be converted into Infix functions.

One of the prominent examples of Infix functions is the to function included in the standard library.

val pair = "Ferrari" to "Katrina"
println(pair)
// (Ferrari, Katrina)

You can define new Infix functions like to as needed. For example, you can extend Int as follows:

infix fun Int.times(str: String) = str.repeat(this)
println(2 times "Hello ")
// Hello Hello

If you want to redefine to as a new Infix function called onto, you can write it as follows:

infix fun String.onto(other: String) = Pair(this, other)
val myPair = "McLaren" onto "Lucas"
println(myPair)
// (McLaren, Lucas)

Such Kotlin syntax enables quite unconventional coding methods.

class Person(val name: String) {
    val likedPeople = mutableListOf<Person>()

    infix fun likes(other: Person) {
        likedPeople.add(other)
    }
}

fun main() {
    val sophia = Person("Sophia")
    val claudia = Person("Claudia")

    sophia likes claudia // !!
}

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Reference

Kotlin Docs