How to Create Lambda in Kotlin: Simple Syntax and Examples

In Kotlin, you create a lambda using the syntax { parameters -> body }. Lambdas are anonymous functions that can be stored in variables or passed as arguments to other functions.

Syntax

A lambda expression in Kotlin is written inside curly braces { }. It can have parameters followed by an arrow -> and then the function body. If there are no parameters, you can omit the arrow.

• Parameters: Variables passed to the lambda.
• Arrow (->): Separates parameters from the body.
• Body: The code executed when the lambda is called.

kotlin

val sum: (Int, Int) -> Int = { a, b -> a + b }

Example

This example shows how to create a lambda that adds two numbers and how to call it.

kotlin

fun main() {
    val add: (Int, Int) -> Int = { x, y -> x + y }
    val result = add(5, 3)
    println("Sum is: $result")
}

Output

Sum is: 8

Common Pitfalls

Common mistakes include forgetting the arrow -> between parameters and body, or mismatching the lambda type with its usage.

Also, if a lambda has only one parameter, you can use it as an implicit name without declaring it.

kotlin

fun main() {
    // Wrong: missing arrow
    // val wrongLambda: (Int) -> Int = { x x * 2 }

    // Correct:
    val correctLambda: (Int) -> Int = { x -> x * 2 }

    // Using implicit 'it' for single parameter
    val implicitIt: (Int) -> Int = { it * 2 }

    println(correctLambda(4))  // Output: 8
    println(implicitIt(5))    // Output: 10
}

Output

8
10

Key Takeaways

Use curly braces with parameters and arrow to create a lambda in Kotlin.

Lambdas can be stored in variables and passed as function arguments.

For single-parameter lambdas, use implicit 'it' to simplify code.

Always match the lambda type with its expected function signature.

Remember the arrow '->' separates parameters from the lambda body.