The Record Type in C#

The record type is a feature introduced in C# 9.0 that allows you to define a reference type that focuses on immutability and structural equality.

Unlike traditional classes, record types are designed to represent data rather than behaviors. This makes them suitable for modeling data, for example.

How to Use record

Defining a Record

To define a record type, the record keyword is used followed by the type name and the list of properties. Below is a basic example:

public record Person(string Name, int Age);

Accessing Properties

Accessing properties of a record is done directly, just like in classes:

Console.WriteLine(person.Name); // Output: Ana
Console.WriteLine(person.Age);   // Output: 30

Structural Equality

Two instances of a record are equal if their properties have the same values:

var person1 = new Person("Ana", 30);
var person2 = new Person("Ana", 30);
var person3 = new Person("Luis", 25);

Console.WriteLine(person1 == person2); // Output: True
Console.WriteLine(person1 == person3); // Output: False

record types automatically override the Equals and GetHashCode methods to provide structural equality.

Immutability

By default, properties of a record are immutable. This means they cannot be modified once the instance has been created.

var product = new Product("Tablet", 300.00m);
// product.Price = 250.00m; // Compilation error: cannot modify a read-only property

Deconstruction

You can deconstruct a record into its individual components using deconstruction syntax:

var (name, age) = person;
Console.WriteLine($"Name: {name}, Age: {age}"); // Output: Name: Ana, Age: 30

Copy with Modification

Although record types are immutable, you can create a copy of a record with some modifications using the with expression.

var product = new Product("Monitor", 200.00m);
var modifiedProduct = product with { Price = 180.00m };

Console.WriteLine(modifiedProduct.Price); // Prints 180.00

Record Inheritance

record types also support inheritance, allowing you to create a hierarchy of record types:

public record Employee(string Name, int Age, string Position) : Person(Name, Age);

Pattern Matching

record types allow the use of pattern matching to compare values and extract data:

public void ShowPerson(Person person)
{
    if (person is Person { Age: >= 18 } adult)
    {
        Console.WriteLine($"{adult.Name} is an adult.");
    }
    else
    {
        Console.WriteLine($"{person.Name} is not an adult.");
    }
}