Introducing C#11: Required properties

Introduction

C# 11 improves the initialization of objects and struct. Marking one or more properties as mandatory on initialization is now possible and will help you not to forget to initialize your properties correctly. In this post I will show you how it works with the object initializer syntax and the object instantiation with a constructor.

Required properties in practical

Marking properties as required requites to add the required keyword on your properties as follow:

	namespace Csharp11Demo.Models;
	public class Car
	{
	public required string Name { get; set; }
	public required int BrandId { get; set; }
	}

view raw Car.cs hosted with by GitHub

When initializing a car object, if you miss initializing a property, for example, the BrandId property, the compiler will raise the following error:

“Error CS9035 Required member ‘Car.BrandId’ must be set in the object initializer or attribute constructor.”

	namespace Csharp11Demo.Models;
	// "Error CS9035 Required member 'Car.BrandId' must be set in the object initializer or attribute constructor."
	var car = new Car { Name = "Toyota" };
	public class Car
	{
	public required string Name { get; set; }
	public required int BrandId { get; set; }
	}

view raw Car.cs hosted with by GitHub

Using a constructor will lead to the same error if you don’t initialize all required properties. Otherwise, if you do not voluntarily initialize your required properties you will have to decorate your class with the SetsRequiredMembers attribute to avoid any compilation error, Examples:

	namespace Csharp11Demo.Models;
	// "Error CS9035 Required member 'Car.BrandId' must be set in the object initializer or attribute constructor."
	var car = new Car("Toyota");
	public class Car
	{
	public required string Name { get; set; }
	public required int BrandId { get; set; }
	public Car(string name)
	{
	Name = name;
	}
	}

view raw Car.cs hosted with by GitHub

	namespace Csharp11Demo.Models;
	// No error
	var car = new Car("Toyota");
	public class Car
	{
	public required string Name { get; set; }
	public required int BrandId { get; set; }
	[SetsRequiredMembers]
	public Car(string name)
	{
	Name = name;
	}
	}

view raw Car.cs hosted with by GitHub

Isn’t practical? . I hope you won’t forget anymore your properties !