Pure Functions

Pure Functions

In this lesson — part of Functional Foundations — you'll learn pure functions in Kotlin and why it matters in real work.

Why it matters

Functional style — pure functions and immutability — makes code easier to test and reason about.

Key ideas

• Pure functions
• Immutability
• No shared mutable state
• Predictable outputs

In practice

Here's how it looks in idiomatic Kotlin:

fun square(x: Int): Int = x * x   // pure: same input -> same output, no side effects

fun main() {
    println(square(5))   // 25
}

Kotlin note: Single-expression functions (fun f() = expr) make small pure functions concise, and val immutability encourages writing them side-effect free.

Try it yourself

Exercise: In Kotlin, rewrite a function that mutates a global so it's pure.

Recap

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