Unlocking the Power of Sealed Classes in Programming
When working with restricted hierarchies, where a value can only take on one of a limited set of types, traditional class structures can fall short. This is where sealed classes come in – a powerful tool that solves a common problem in programming.
The Problem with Traditional Class Structures
Consider a scenario where you have a base class Expr with two derived classes Const and Sum. In this setup, it’s mandatory to include an else branch for default conditions in when expressions. But what happens when you add a new subclass? The compiler won’t detect anything, and you may end up with bugs. It would be ideal if the compiler could issue an error when you introduce a new subclass.
Introducing Sealed Classes
Sealed classes provide a solution to this problem by restricting the possibility of creating subclasses. By using the sealed modifier, you can ensure that all subclasses are handled in a when expression, eliminating the need for an else branch. This means that if you derive a new subclass, the compiler will complain unless it’s handled in the when expression.
Key Characteristics of Sealed Classes
There are a few important notes to keep in mind when working with sealed classes:
- All subclasses must be declared in the same file as the sealed class.
- A sealed class is abstract and cannot be instantiated directly.
- Constructors of a sealed class are private by default and cannot be made non-private.
Sealed Classes vs. Enums: What’s the Difference?
Sealed classes and enums share some similarities, as both restrict the set of possible values. However, there’s a key difference: enums can only have a single instance, whereas a subclass of a sealed class can have multiple instances.
By leveraging sealed classes, you can write more robust and maintainable code, ensuring that your programs are less prone to errors and bugs. So why not give them a try?