Kotlin infix function notation

In this article, we will learn infix notation used in Kotlin functions. In Kotlin, a functions marked with infix keyword can also be called using infix notation means calling without using parenthesis and dot.

There are two types of infix function notation in Kotlin-

  1. Standard library infix function notation
  2. User defined infix function notation

Standard library infix function notation –

When we call operators like and, or , shr, shl etc then compiler looks for the function and calls the desired one. There is a number of standard library infix notations functions but we will discuss here some of them.

Let’s discuss some of infix notations one by one.

1. Koltin program using bitwise and operator –

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fun main(args: Array<String>) {
    var a = 15
    var b = 12
    var c = 11
    // call using dot and paranthesis
    var result1 =(a > b).and(a > c)           
    println("Boolean result1 = $result1")
    // call using infix notation
    var result2 =(a > b) and (a > c)          
    println("Boolean result1 = $result2")
}

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Output:

Boolean result1 = true
Boolean result1 = true

Explanation:
Here, we have called the a.and(b) function using infix (a and b).
Both produce the same result in the standard output.

2. Kotlin program of using signed shift right(shr) operator –

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fun main(args: Array<String>) {
    var a = 8
  
    // // call using infix notation
    var result1 = a shr 2
    println("Signed shift right by 2 bit: $result1")
    // call using dot and parenthesis
    var result2 = a.shr(1)
    println("Signed shift right by 1 bit: $result2")
}

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Output:

Signed shift right by 2 bit: 2
Signed shift right by 1 bit: 4

Explanation:
In the above program, we have used signed shift operator. First, performed the operation using the infix notation then performed using dot and parenthesis.
If we signed shift the value by 2 bits then 23=8 becomes 2(3-2=1)=2.

3. Kotlin program of using increment and decrement operators –

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fun main(args: Array<String>) {
    var a = 8
    var b = 4
     
    println(++a)      // call using infix notation
    println(a.inc())  // call using dot and parenthesis
    println(--b)      // call using infix notation
    println(b.dec())  // call using dot and parenthesis
}

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Output:

9
10
3
2

Explanation:
Here, we have used increment and decrement operators using infix notations.
++a represents a(8) + 1 so it prints 9
a.inc() also represents a(9) + 1 so it prints 10
–b represents b(4) – 1 = 3
b.dec() also represents b(3)- 1 = 2

User defined infix function notation –

We can create own function with infix notation if the function satisfy the following requirements:

  • It must be member function or extension function
  • It must accepts a single parameter
  • The parameter must not accept variable number of arguments and must have no default value
  • It must be marked with infix keyword

Kotlin program of creating square function with infix notation –

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class math {
    // user defined infix member function
    infix fun square(n : Int): Int{
        val num = n * n
        return num
    }
}
fun main(args: Array<String>) {
   val m = math()
    // call using infix notation
    val result = m square 3
    print("The square of a number is: "+result)
}

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Output:

The square of a number is: 9

Explanation:
In the above program, we have created own infix notation function (m square 3).
1. First of all, we defined the infix the infix notation function within a class math because it must be member function.
2. infix keyword used to mark the function.
3. It contains only one parameter and having no default value and function return type is also Integer.

square(n : Int):Int

Then, we create an object for the class math()
and called the function using infix notation-

m square 3

It calculate the square of the number and returns value 9

Kotlin program to check the data type of variable with infix notation –

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class check{
    // user defined infix member function
    infix fun dataType(x: Any):Any{
    var i = when(x){
            is String -> "String"
            is Int -> "Integer"
            is Double -> "Double"
            else -> "invalid"
        }
        return i
    }
}
fun main(args: Array<String>){
    var chk = check()
    // call using infix notation
    var result = chk dataType 3.3
    println(result)
}

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Output:

Double

Explanation:
We have created an infix notation function to find the datatype of variable.
The datatype has been passed as an argument in infix call-

chk dataType 3.3

when checks data type for the passing parameter and returns the desired value.
Here, it returns Double to the standard output.

Precendence of infix function with operators-

Precedence matters at the time of execution of an instruction. Infix function calls have lower precedence than the arithmetic operators, type casts, and the rangeTo operator.

The following expressions are equivalent:

2 shr 1 + 2 and 2 shr (1 + 2)
1 until n * 2 and 0 until (n * 2)
xs union ys as Set<*> and xs union (ys as Set<*>)

On the other hand, infix function call have higher precedence than the boolean operators && and ||, is- and in-checks, and some other operators.
The following expressions are equivalent as well:

a xor b || c and a xor (b || c)
a in b xor c and a in (b xor c)


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