10 Functional Programming Tips Every C# Developer Should Know

Functional programming

Alex Maher


I remember the first time I stumbled upon the term “functional programming” while coding in C#. It sounded intimidating, but then I gave it a shot, and let me tell you, it was something new.

We’re going to walk through 10 functional programming tips that have seriously helped me writing C# code. These aren’t just fancy tricks; they’re practical, hands-on tweaks that make code cleaner, more efficient, and honestly, more fun to write.

Let’s dive in!


Immutability is a core concept in functional programming (FP) and is crucial for writing robust and maintainable C# code. In FP, immutability is about creating new instances of data with the desired changes rather than updating data in place.

This approach ensures that functions are pure, meaning their output is determined solely by their input, without any side effects.

Code examples:

Creating New Instances Instead of Mutating

var originalList = new List<int> { 1, 2, 3 };
var newList = originalList.Append(4).ToList();

Here, Append does not modify the original list but returns a new list with the additional element.

Using Immutable Collections

var list = ImmutableList<int>.Empty;
list = list.Add(1);

ImmutableList ensures that the original collection remains unchanged when modifications are made.

Immutable Objects

public class ImmutableProduct
public int Inventory { get; }
private ImmutableProduct(int inventory)
Inventory = inventory;
public ImmutableProduct ReplenishInventory(int units)
return new ImmutableProduct(Inventory + units);

This ImmutableProduct class does not allow direct mutation of its Inventory property. Instead, it provides a method to create a new instance with the updated inventory.

Performance Considerations



Alex Maher

.NET C# dev with 10+ yrs exp, self-taught & passionate web developer. Sharing tips & experiences in C# and web dev.