Introducing C# 10: Record struct
source link: https://anthonygiretti.com/2021/08/03/introducing-c-10-record-struct/
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
Introducing C# 10: Record struct
Introduction
Last year with the release of C# 9, Microsoft introduced records. The record keyword gives a reference
type new superpowers like immutability declared with positional records (or by using init-only properties), equality comparisons that mimic value types, and with-expressions that allows you to create a new record instance with the same property values, the properties you need to change. This drastically simplifies the process to copy objects.
This year, C# 10 brings records structs. They’ll carry a lot of the advantages of C# 9 records (which are reference types, like classes), but don’t get fooled: there are differences with structs because…. structs are different from classes!
In this article, we will see what a record struct is, and why a record class doesn’t behave like a record struct.
If you need a reminder on record class, you read this post:
https://anthonygiretti.com/2020/06/17/introducing-c-9-records/
This article has been made with my friend Dave Brock and I would like to take the opportunity to thanks him. I you wanna follow him you can find his post and his social medias infos: https://www.daveabrock.com/.
Syntax
First of all, Microsoft has made an improvement to record classes. With C# 9, to declare a record you replaced the “class” keyword with “record.” To avoid confusion when declaring structs as records, C# 10 allows a new syntax to declare a class as a record by mixing record and class keywords:
public record class Product {}The C# 9 syntax remains valid:
public record Product {}Declaring a struct as a record looks like this:
public record struct Product {}It’s a more convenient approach to avoid confusion between a record class and a record struct. A record struct is a struct with all its struct properties and a record class is a class with all its class properties.
Immutability
Init-only properties are allowed on record structs:
public record struct Product { public string Name { get; init; } public int CategoryId { get; init; } }
If you try to reassign a property that has the init keyword set after its initialization you’ll get a compilation error:
using System;
public class Program { public static void Main() { var product = new Product { Name = "VideoGame", CategoryId = 1 };
product.Name = ""; // Error CS8852 Init-only property or indexer 'Product.Name' can only be assigned in an object initializer, or on 'this' or 'base' in an instance constructor or an 'init' accessor. } }
Using positional records is quite different for record structs. Positional records on struct doesn’t make the record immutable as a record class. Because it’s a struct you have to set the readonly keyword to make the record struct immutable. The following code is equivalent to the previous declaration above:
public readonly record struct Product(string Name, int CategoryId);
With-expressions
Like a record class, a record struct allows the usage of with-expressions and works similarly to a record class:
using System;
public class Program { public static void Main() { var product = new Product { Name = "VideoGame", CategoryId = 1 };
var newProduct = product with { CategoryId = 2 }; } }
Equality comparison
Because a record struct is a struct, comparing (with Equals method) two structs that have the same values will always return true. A struct is a value type, unlike a class. A regular struct doesn’t implement == and != operators, so it’s impossible to compare two structs with these operators. However, the comparison with these operators is allowed on a record struct:
using System;
public class Program { public static void Main() { var product1 = new Product { Name = "VideoGame", CategoryId = 1 };
var product2 = new Product { Name = "VideoGame", CategoryId = 1 };
Console.WriteLine(product1.Equals(product2)); // Returns true
Console.WriteLine(product1 == product2); // Returns true. Only allowed on record structs, not allowed on regular structs } }
Printing members
Record structs implement a new override of the ToString() method that allows printing a structured string of the struct record. With the same signature of Product struct, let’s compare the output:
public class Program { public static void Main() { var product1 = new Product { Name = "VideoGame", CategoryId = 1 };
Console.WriteLine(product); // Will output: Product { Name= VideoGame, CategoryId = 1 } } }
If Product is a regular struct:
Id Product is a record struct:
Performance
In terms of performance, structs offer performance benefits. In some benchmarks, using record structs is 20 times faster than a regular struct. A future post will show off detailed benchmarks.
Conclusion
This article aimed to introduce record struct with C# 10. Because it’s a big feature, probably the most in C# 10, I probably missed some aspects of record structs. At this time of writing C# 10 is still in preview, and this article may evolve once C# 10 is released.
Hope you’ll enjoy record structs, personnaly I love it! 
Like this:
Recommend
About Joyk
Aggregate valuable and interesting links.
Joyk means Joy of geeK