Lambda Expression Basics in Kotlin

Introduction

Lambda Expression Basics is a fundamental concept every Kotlin developer should understand. Lambda expressions are anonymous functions you can pass as values — the foundation of functional-style APIs in Kotlin.

Lambda is a function literal written without a name. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• Lambda is a function literal written without a name.
• It can be passed as a value to other functions.
• Syntax: { parameters -> body }.

Syntax

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

Lambda Expression Basics in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val add = { a: Int, b: Int -> a + b }
    println("Sum: ${add(4, 6)}")
}

Sample Output

Sum: 10

When to use

Use lambdas for short callbacks passed to collection operations, event handlers, or higher-order functions.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. val add = { a: Int, b: Int -> a + b } assigns or updates a value used later in the program.

3. The println("Sum: ${add(4, 6)}") statement writes a line to the console — this produces part of the sample output below.

4. Lambda is a function literal written without a name.

5. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

• Keep lambdas short; extract longer logic into named functions.
• Use it only when the lambda has a single parameter and the meaning is obvious.
• Prefer trailing lambda syntax when the last argument is a function.

Common Mistakes

• Capturing mutable variables unsafely in concurrent lambdas.
• Over-nesting lambdas when a named function would be clearer.
• Forgetting that return inside a lambda returns from the lambda, not the outer function (unless inline).

Key Points

• Lambda is a function literal written without a name.
• It can be passed as a value to other functions.
• Syntax: { parameters -> body }.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.