Careeroza

Single-Expression Functions

Using = Instead of a Body

Example

When a function just returns one expression, write = expression. The return type can usually be inferred.

fun square(x: Int) = x * x
fun isEven(n: Int) = n % 2 == 0
fun fullName(first: String, last: String) = "$first $last"
fun maxOf3(a: Int, b: Int, c: Int) = maxOf(a, maxOf(b, c))
fun gstOf(amount: Int): Int = amount * 18 / 100

fun main() {
    println(square(9))
    println(isEven(10))
    println(fullName("Virat", "Kohli"))
    println(maxOf3(4, 19, 7))
    println(gstOf(1000))
}

Output

81
true
Virat Kohli
19
180

Combining with when and if

Example

Single-expression functions pair nicely with if and when expressions.

fun signOf(n: Int) = when {
    n > 0 -> "positive"
    n < 0 -> "negative"
    else -> "zero"
}

fun ticketPrice(age: Int) = if (age < 12) 100 else 200

fun main() {
    println(signOf(-4))
    println(signOf(0))
    println(ticketPrice(8))
    println(ticketPrice(30))
}

Output

negative
zero
100
200

Note: Write the return type explicitly for public functions in libraries, so a change in the body does not silently change the API.