Closures and Higher-Order Functions

Closures and Higher-Order Functions

In this lesson — part of Advanced Features — you'll learn closures and higher-order functions in Kotlin and why it matters in real work.

Why it matters

Functions that take or return functions unlock concise, composable code.

Key ideas

• Functions as values
• map / filter / reduce
• Callbacks
• Composition

In practice

Here's how it looks in idiomatic Kotlin:

fun main() {
    val nums = listOf(1, 2, 3, 4, 5, 6)
    val result = nums.filter { it % 2 == 0 }   // keep evens
                     .map { it * it }          // square them
    println(result)   // [4, 16, 36]
}

Kotlin note: filter and map take lambdas where the single parameter is implicitly named it, and chaining them reads top-to-bottom like a pipeline.

Try it yourself

Exercise: In Kotlin, use map and filter to get the squares of the even numbers.

Recap

You now understand closures and higher-order functions and can apply it in Kotlin. Mark this lesson complete and continue to the next one.