Should You Inherit from Standard Containers?

Subtyping Standard Containers: A Cautionary Tale

It has been a common topic of discussion on Stack Overflow whether inheriting from standard containers is a sound practice. While the concern has been raised that standard containers lack virtual destructors, this article aims to delve deeper into the reasons why subtyping standard containers should generally be avoided.

Perils of Lacking Virtual Destructors

The absence of virtual destructors in standard containers poses a serious challenge for polymorphic usage. Without virtual destructors, there is no guarantee that cleanup will be performed correctly in derived classes, leading to potential memory leaks and undefined behavior.

Design Flaws of Inheriting Containers

Even if virtual destructors were present, inheriting from containers still constitutes poor design. Instead of extending functionality through inheritance, it is preferable to use generic algorithms that work across all containers. This approach promotes code reuse and maintainability.

Inheriting from containers also compromises encapsulation. By breaking encapsulation, it becomes difficult to modify or maintain the internal workings of the container. Instead, it is better to keep the container's interface separate and introduce new behavior through external code, such as namespace-scope functions or containment in a new class.

Inheritance as a Misguided Means

Lastly, it is crucial to dispel the notion that inheritance is a suitable mechanism for extending behavior. This misconception has led to monolithic designs that are prone to rigidity and versioning issues.

Instead of inheriting to extend behavior, it is advisable to favor composable designs that allow components to be combined and recombined flexibly. Inheritance should primarily be used to enforce the Open/Closed Principle, where classes are open for extension but closed for modification.

In summary, inheriting from standard containers should be treated with caution. Lack of virtual destructors, design deficiencies, and the pitfalls of using inheritance for behavior extension all point to the superiority of alternative approaches, such as generic algorithms, composable designs, and the Open/Closed Principle.

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