Code Housekeeping - Part 9 - Seal Classes & Records By Default

Code Housekeeping refers to general rules of thumb that make code easier to read, digest, and modify for other developers, yourself included.

If I were to open any of your projects, I can bet almost all of your classes will look like this:

public class Car
{
    public required string Name { get; set; }
    public required string Model { get; set; }
    public required int YearOfManufacture { get; set; }

    public override string ToString()
    {
        return $"{Name}, {Model} ({YearOfManufacture})";
    }
}

Your modifiers is almost always public .

This means that any downstream user can extend your class.

public class SportsCar : Car
{
    public required int MaxSpeed { get; set; }

    public override string ToString()
    {
        return $"This a Sports {Name}, {Model}";
    }
}

But why is that by default the class is extensible?

The reality is a class that allows extensibility must be designed with extensibility in mind. This is almost always not the case.

Get into the habit of sealing your classes by default, like this:

public sealed class Car
{
  public required string Name { get; set; }
  public required string Model { get; set; }
  public required int YearOfManufacture { get; set; }

  public override string ToString()
  {
  	return $"{Name}, {Model} ({YearOfManufacture})";
  }
}

By default, you cannot extend this.

If later down the road you, or a downstream user requires to extend the class, a conversation can be had about it, and the appropriate design modifications can be done to the class to allow this.

Otherwise trying to inherit a sealed class gives you a compiler error:

If i had my way I would have the default modifier for modern IDEs to be sealed for any new code.

Fun fact - in the Kotlin language classes are sealed by default.

TLDR

Seal classes by default, until a need arises to extend them.

The code is in my GitHub.

Happy hacking!