Exploring C# 10: Use Extended Property Patterns to Easily Access Nested Properties

17 Nov 2021

Welcome back to my series on new C# 10 features. So far we've talked about file-scoped namespaces and global using declarations. Today, we'll talk about extended property patterns in C# 10.

Over the last few years, C# has made a lot of property pattern enhancements. Starting with C# 8, the language has supported extended property patterns, a way to match an object's specific properties.

For our example, let's continue the superhero theme with a Person, a Superhero that inherits from Person, and a Suit. We're going to calculate any special surcharges when making a particular superhero's suit.

public class Person
{
    public string? FirstName { get; set; }
    public string? LastName { get; set; }
    public string? Address { get; set; }
    public string? City { get; set; }
}

public class Superhero : Person
{
    public int MaxSpeed { get; set; }
    public Suit? Suit { get; set; }
}

public class Suit
{
    public string? Color { get; set; }
    public bool HasCape { get; set; }
    public string WordsToPrint { get; set; }
}

Now let's create a quick object for Iron Man:

var tonyStark = new Superhero()
{
    FirstName = "Tony",
    LastName = "Stark",
    Address = "10880 Malibu Point",
    City = "Malibu",
    Suit = new Suit
    {
       Color = "Red",
       HasCape = false
    }
};

In our switch expression, let's say we want to determine special pricing based on a particular suit's color.

Here's how we'd do it in C# 9:

public static int CalculateSuitSurcharge(Superhero hero) =>

        hero switch
        {
            { Suit: { Color: "Blue" } } => 100,
            { Suit: { Color: "Yellow" } } => 200,
            { Suit: { Color: "Red" } } => 300
            _ => 0
        };

With C# 10, we can use dot notation to make it a bit cleaner:

public static int CalculateSuitSurcharge(Superhero hero) =>

        hero switch
        {
            { Suit.Color: "Blue" } => 100,
            { Suit.Color: "Yellow" } => 200,
            { Suit.Color: "Red" } => 300
            _ => 0
        };

Much like before, you can also use multiple expressions at once. Let's say we wanted to charge a surcharge for a notoriously difficult customer. Look at how we can combine multiple properties in a single line.

public static int CalculateSuitSurcharge(Superhero hero) =>

        hero switch
        {
            { Suit.Color: "Blue" } => 100,
            { Suit.Color: "Yellow" } => 200,
            { Suit.Color: "Red", Address: "10880 Malibu Point" }  => 500,
            { Suit.Color: "Red" } => 300
            _ => 0
        };

That's all there is to it. Will this feature change your life? No. Even so, it's a nice update that allows for cleaner and simpler code.

There's a lot more you can do with property patterns as well, so I'd recommend hitting up the Microsoft Docs to learn more.