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Code Smell 32 - Singletons

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.
Originally published at maximilianocontieri.com Updated on ・2 min read

The most used and (in)famous design pattern in the world is causing us great harm.

Problems

  • Coupling

  • Testability

  • Accidental implementation problems.

  • Multi threading issues.

  • Static methods polluting.

  • Object creation contract violation.

  • Bijection mismatch.

  • Memory issues.

  • Premature Optimization.

Solutions

  1. Avoid it.

  2. Use contextual unique objects.

  3. Benchmark object creation.

Examples

  • Database Access

  • Globals

  • Loggers

  • Helpers

Sample Code

Wrong

God is the archetypical singleton example.

Right

Detection

This is a design pattern. We should avoid it by policy.

We can add linter rules for patterns like 'getInstance()' so new developers cannot infect code with this anti-pattern.

Tags

  • Globals

Conclusion

This is an historical mistake already acknowledged by the community. Nevertheless, lazy developers bring it again and again. We need to reach a consensus on its drawbacks.

Relations

More info

Credits

Photo by Maria Teneva on Unsplash


The Diagram is Not the Model. The model is not the diagram. It is an abstraction, a set of concepts and relationships between them.

Eric Evans

Discussion (2)

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yoursunny profile image
Junxiao Shi

How is GodFactory supposed to be used if it always throws?

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mcsee profile image
Maxi Contieri Author

Hi. I changed the example and removed factory usage since I think it was a bit confusing