Cloning Considered Harmful

Considered Harmful?

presented byNicolas Bettenburg

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10-15% cloned!

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Intentional e.g., Copy & Paste

Unintentional e.g., Language Idioms

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Cloning = additional maintenance effort

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Clones consideredharmful!

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But Wait!Is that the right thing

to do?

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Example: Cloning to experiment without risk

experimental

stable

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Understand Reasonbehind duplicationbefore deciding!

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Catalogue of High-Level Cloning Patterns

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8 general cloning patterns

CustomizationTemplatingForking

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Hardware Variations

Clone existing driver+ No risk of changing existing driver- Code growth~ Dead code can creep into system

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Clone existing code and fix low level platform interaction+ Avoid complexity of virtualization layer- Hard to propagate bug fixes~ Ensure consistent behavior of all clones

Platform Variations

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Clone existing code and experiment+ Maintain stable code- Merging later may be difficult~ Consistent maintenance becomes difficult

Experimental Variations

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Cloning due to language constraints+ Make reuse of trusted code possible- Increased maintenance (close evolution)~ Explicit and rigorous linking of all duplicates

Boiler-plating

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Clone reoccurring call sequences+ Learn from code and reduce effort- Degradation of Code Quality~ Changes to API require maintenance of all clones

API/Library Protocols

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Idioms provide standardization+ Selfdocumenting and improve comprehensibility- Faulty implementations are easily overlooked~ no long term issues

Language Idioms

a = malloc(64);if (a == null) {out(“Error!”);

}...

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Clone to provide work arounds+ Clone buggy code and fix- Source of the bug is not addressed~ Remove clone when bug is fixed

Bug Workarounds

...a = sqroot(81);if (a != 9) {a = 9;

}...

...a = sqroot(81);...

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Clone to reuse and adapt existing solutions+ Less effort needed- Long-term cost outweighs short-term benefit~ Cost of refactoring rises over time

Replicate & Specialize

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Conclusions

•Templating requires synchronization•Variation requires monitoring of changes•Forking need outlining

•Not all clones require refactoring•Some situations warrant the effort•Measure risk vs. long-term cost

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Considering Cloning harmful in general can be harmful!

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