How to create immutable objects in C#?

Question

In a question about Best practices for C# pattern validation, the highest voted answer says:

I tend to perform all of my validation in the constructor

Answer 1

C# 9 is coming up with new feature names as Record. Init-only properties are great if you want to make individual properties immutable. If you want the whole object to be immutable and behave like a value, then you should consider declaring it as a record:

public data class Person
{
    public string FirstName { get; init; }
    public string LastName { get; init; }
}

The data keyword on the class declaration marks it as a record.

Reference: https://devblogs.microsoft.com/dotnet/welcome-to-c-9-0/#records