# [Kotlin] What is Infix Functions?

## GOAL

To understand infix functions in Kotlin.

## What is infix function?

In Kotlin, *functions marked with the infix keyword can also be called using the infix notation* (sited from the documentation of Kotlin). An example follows.

infix fun Int.add(a:Int): Int { return this+a }

## What is infix notation?

Infix notation is one of the notation types. In infix notation the operator is described in thee middle of the targets. + – * / are usually used as infix notation. (1+2, a-b)

- Infix notation
- (1+2)*(3-4)

- Prefix notation (Polish notation)
- *+12-34

- Postfix notation (Reverse Polish notation)
- 12+34-*

## Implementation in Kotlin

fun pre_add(a:Int, b:Int): Int{ return a+b } infix fun Int.in_add(a:Int): Int { return this+a } infix fun Int.in_sub(a:Int): Int = this-a fun main() { println(pre_add(1,2)) println(1 in_add 2) println(1.in_add(2)) println(1 in_sub 2) println(1.in_sub(2)) }

output

3 3 3 -1 -1