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Cover image for Code Smell 43 - Concrete Classes Subclassified

Code Smell 43 - Concrete Classes Subclassified

Maxi Contieri
Learn something new every day. - I am a senior software engineer working in industry, teaching and writing on software design, SOLID principles, DDD and TDD.
Updated on ・1 min read

Inheritance. Concrete classes. Reuse. A fantastic mix up.

Problems

Solutions

  1. Subclasses should be specializations.

  2. Refactor Hierarchies.

  3. Favor Composition.

  4. Leaf classes should be concrete.

  5. Not leaf classes should be abstract.

Sample Code

Wrong

Right

Detection

Overriding a concrete method is a clear smell. We can enforce these policies on most linters.

Abstract classes should have just a few concrete methods. We can check against a predefined threshold for offenders.

Tags

  • Composition

Conclusion

Accidental sub-classification is the first obvious advantage for junior developers.

More mature ones find composition opportunities instead.

Composition is dynamic, multiple, pluggable, more testable, more maintainable and less coupled than inheritance.

Only sub-classify an entity if it follows the relationships behaves like.

After sub-classing the parent class should be abstract.

Relations

More info

Wikipedia


Software is a gas; it expands to fill its container.

Nathan Myhrvold

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