Why might you want a class to have the sealed attribute?

I'm currently building my first big project relying heavily on super/subclasses for the structure of the project, so I've been learning a lot about how classes work in MATLAB.

I was looking through the class attribute page recently when I saw the 'sealed' attribute and it has me wondering what the point of it is. I understand that it prevents subclassing (and some searching on the forums seems to show that it's used for several native MATLAB classes), but my real question is why would you want to prevent that? It seems to imply that classes could be built in such a way that subclassing them could cause issues or unintended behavior, hence the desire to seal them. But I can't imagine how subclassing could cause such an issue or behavior.

So, my question would be: When should one consider using this attribute, and what kind of issues does it help avoid?

Answer 1

[Milan Bansal]

Hi Aaron Coville

The sealed attribute in MATLAB prevents a class from being subclassed (inherited from). When a class is marked as sealed, it means that other classes cannot extend or inherit from it. This can be useful in scenarios where:

1. Ensuring Control over Class Behavior: By sealing a class, you ensure that the intended behavior of the class remains consistent and cannot be altered or extended. This is important if you want to maintain strict control over the class's functionality, especially when certain behaviors or patterns must remain unchanged for the integrity of the application.
2. Preventing Inappropriate Inheritance: There may be cases where the class design does not lend itself well to extension, and allowing others to subclass it could lead to unforeseen issues, such as incorrect use of the base class's internal state or breaking intended encapsulation.

When to Use:

• If your class is designed with specific functionality that should not be extended or altered.
• When performance is critical, and you're looking to take advantage of any optimizations MATLAB may apply to sealed classes.
• If you want to enforce strict usage patterns to avoid misuses of your class in unintended ways.

Issues it Helps Avoid:

• Unintended Overrides: Without sealing, methods or properties might be accidentally or intentionally overridden, leading to unexpected behavior.
• Maintenance Complexity: Allowing subclassing can introduce more complexity when maintaining the code, as subclasses may introduce dependencies or conflicting behaviors.

Please refer to following documentation link to learn more about "class attributes"

https://www.mathworks.com/help/matlab/matlab_oop/class-attributes.html

Hope this helps!