If you’ve started learning Kotlin — especially for Android or Jetpack Compose — you’ve definitely bumped into lambda functions.
They show up everywhere. Sometimes they’re cute and helpful. Sometimes they look like hieroglyphics.

But don’t worry — by the end of this article, you’ll understand:

✔️ What lambda functions are
✔️ How to use them (with super simple examples)
✔️ Returning values from lambdas
✔️ Lambdas that return Unit
✔️ What the magical keyword it means
✔️ What the heck trailing lambdas are (with real-world Jetpack Compose examples)

Let’s begin!

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🎯 What Is a Lambda Function in Kotlin?

A lambda function is basically a short, anonymous function — a function without a name.

Think of it as a mini-function you can pass around like a variable.

Syntax:

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

You can call it like a normal function:

println(add(10, 5))  // 15

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🧁 Why Do We Even Need Lambdas?

Because writing full functions everywhere gets boring:

fun greet(name: String): String {
    return "Hello $name"
}

Instead:

val greet = { name: String -> "Hello $name" }

Less typing → more fun → fewer tears.

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🟩 1. Basic Lambda Examples

1. Lambda with parameters:

val square = { n: Int -> n * n }
println(square(4))  // 16

2. Lambda with no parameters:

val sayHello = { println("Hello Kotlin!") }
sayHello()

3. Lambda stored as a function type:

val multiply: (Int, Int) -> Int = { x, y -> x * y }

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🟦 2. Return Values in Lambdas

In Kotlin lambdas, the last line is automatically the return value — no return keyword needed.

val message = { name: String ->
    val upper = name.uppercase()
    "Hello $upper"
}

Return value = "Hello AMIT"

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🟨 3. Lambdas That Return Unit

Unit = “nothing meaningful is returned”

It’s Kotlin’s version of void.

Example:

val logMessage: (String) -> Unit = { msg ->
    println("LOG: $msg")
}

Usage:

logMessage("App started")

If you don’t specify return type, Kotlin figures it out:

val doSomething = {
    println("Doing something important...")
}  // returns Unit implicitly

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🟧 4. Understanding it — Kotlin’s Favorite Keyword

If your lambda has only one parameter, you don’t need to name it. Kotlin automatically names it it.

Example WITHOUT it:

val double = { x: Int -> x * 2 }

Example WITH it:

val double = { it * 2 }

Cleaner. Simpler.

Real-world analogy:

Instead of saying:
“Give this apple to the fruit-checker, and the fruit-checker will inspect the apple”

You say:
“Give it to the fruit-checker, they’ll inspect it.”

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🟪 5. Trailing Lambdas — The Most Confusing Kotlin Feature (Explained Simply)

✔ First, the basic idea:

If the last argument of a function is a lambda,
you can put the lambda outside the parentheses.

Normal way:

repeat(3, { println("Hello") })

Trailing lambda way:

repeat(3) {
    println("Hello")
}

Much cleaner!

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🍕 Trailing Lambda — Simple Example

Without trailing lambda:

fun greet(times: Int, block: () -> Unit) {
    repeat(times, block)
}

greet(2, { println("Hi!") })

With trailing lambda:

greet(2) {
    println("Hi!")
}

Better for readability.

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📱 Trailing Lambdas in Jetpack Compose (Real Example)

Compose uses lambdas everywhere because UI is declarative.

Example 1 — Button

Button(onClick = { 
    println("Button clicked!") 
}) {
    Text("Click Me")
}

Notice:

• onClick is a lambda
• The content of the button (children UI) is also a lambda
• This is why Compose reads like a storybook

Same thing but cleaner:

Button(onClick = { println("Clicked!") }) {
    Text("Click Me")
}

Here, the trailing lambda is the button content.

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🔥 Real-World Jetpack Compose Example (Explains Trailing Lambda Clearly)

Imagine a card UI:

Card(
    modifier = Modifier.padding(16.dp),
    elevation = 8.dp
) {
    Column(Modifier.padding(16.dp)) {
        Text("Welcome Amit!")
        Text("Jetpack Compose loves lambdas.")
    }
}

The last curly block:

{
    Column(...) { ... }
}

👉 That’s a trailing lambda providing the UI content for the card.

Compose = functions + trailing lambdas = flexible UI.

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🧠 Summary (You’re Now a Lambda Pro)

Concept	Meaning
Lambda	Anonymous mini-function
Return in lambda	Last line = return value
Unit return	Lambda returns nothing (like void)
it keyword	Auto-name for single-parameter lambdas
Trailing lambda	Move last lambda parameter outside parentheses
Compose usage	Everything in Compose is built with lambdas

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🎉 Final Thoughts

Kotlin lambdas may look intimidating at first, but once you get used to them, they make your code:

• shorter
• cleaner
• easier to read
• perfect for Jetpack Compose

Now that you understand them, Compose UI will suddenly start making a LOT more sense.
Every {} block you see? Yep — it’s all lambdas!