Pure Functions

Pure Functions

In this lesson — part of Functional Foundations — you'll learn pure functions in Go 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 Go:

package main

import "fmt"

func square(n int) int { // pure: no side effects, output depends only on input
	return n * n
}

func main() {
	fmt.Println(square(5)) // 25
}

Go note: A pure function in Go reads no global mutable state and writes none, so the same input always yields the same output.

Try it yourself

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

Recap

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