Pure Functions

Pure Functions

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

// Pure: output depends only on inputs, no side effects
static int Square(int x) => x * x;

int result = Square(5);   // always 25
Console.WriteLine(result);

C# note: Marking such helpers 'static' signals they capture no instance state, reinforcing purity (no hidden 'this' dependency).

Try it yourself

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

Recap

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