Introducing C# 10: Extended property patterns

Introduction

C# 8 has introduced a new pattern: Property pattern. This pattern enables you to match on properties of the object examined, if you missed that feature, here is the Microsoft documentation here: Property pattern. C# 10 improves that pattern by simplifying access to nested properties. In the article I’ll show what it is.

Example

The following code sample shows a C# 8 tax calculator, which involves an object named CalculateTax and its nested property named ProvinceOrStateTaxProperty which is itself an object:

	namespace DemoCsharp9
	{
	public class ProvinceOrStateTaxProperty
	{
	public string ProvinceOrState { get; set; }
	}
	public class CalculateTax
	{
	public string CountryName { get; set; }
	public ProvinceOrStateTaxProperty ProvinceTaxProperty { get; set; }
	}
	public class Computing
	{
	private static decimal ComputePrice(CalculateTax calculate, decimal price) =>
	calculate switch
	{
	{ ProvinceTaxProperty: { ProvinceOrState: "Québec" } } => 1.14975M * price,
	{ ProvinceTaxProperty: { ProvinceOrState: "Alberta" } } => 1.05M * price,
	{ ProvinceTaxProperty: { ProvinceOrState: "Ontario" } } => 1.13M * price,
	_ => 0
	};
	}
	}

view raw Computing.cs hosted with by GitHub

The syntax to access the nested property is a bit verbose:

{ ProvinceTaxProperty: { ProvinceOrState: "Value" } }

C# 10 fixes that and allows to access directly the nested property by a dot:

	namespace DemoCsharp10
	{
	public class ProvinceOrStateTax
	{
	public string ProvinceOrState { get; set; }
	}
	public class CountryTax
	{
	public string CountryName { get; set; }
	public ProvinceOrStateTax ProvinceTaxProperty { get; set; }
	}
	public class Computing
	{
	private static decimal ComputePrice(CountryTax calculate, decimal price) =>
	calculate switch
	{
	{ ProvinceTaxProperty.ProvinceOrState: "Québec" } => 1.14975M * price,
	{ ProvinceTaxProperty.ProvinceOrState: "Alberta" } => 1.05M * price,
	{ ProvinceTaxProperty.ProvinceOrState: "Ontario" } => 1.13M * price,
	_ => 0
	};
	}
	}

view raw Computing.cs hosted with by GitHub

Much more practical isn’t it ?