House of Cards: Code Smells in Open-source C# Repositories
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This study analyzed over 1,988 open-source C# repositories on GitHub to detect 30 code smells, including 19 design smells and 11 implementation smells. The most frequently occurring smells were Magic Number (over 2.9 million instances), Unutilized Abstraction (over 90,000 instances), and Duplicate Abstraction (over 73,000 instances). There was a strong positive correlation between the occurrence of design smells and implementation smells. Certain smells also tended to co-occur within their category. Finally, design smell density decreased but implementation smell density increased as project size grew.
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House of Cards: Code Smells in Open-source C# Repositories
- 1. House of Cards: Code Smells in Open-source C# Repositories Tushar Sharma, Marios Fragkoulis, and Diomidis Spinellis Funded by SENECA project under Marie-Skłodowska Curie Actions
- 3. Code Smells …certain structures in the code that suggest (sometimes they scream for) the possibility of refactoring. - Kent Beck <!>
- 4. http://www.tusharma.in/smells/ A Taxonomy of Software Smells
- 5. Identified gap • Existing mining studies on smells lack • scale (Number of subject systems analyzed), and • breadth (Number of smells detected) • Solely performed on Java subject systems
- 6. Overview of the study Research questions 1988 open-source repositories Designite <!> 19 Design smells 11 Implementation smells Results
- 7. Detected design smells Abstraction smells: • Duplicate Abstraction • Imperative Abstraction • Multifaceted Abstraction • Unnecessary Abstraction • Unutilized Abstraction Encapsulation smells: • Deficient Encapsulation • Unexploited Encapsulation Modularization smells: • Broken Modularization • Cyclically-dependent Modularization • Hub-like Modularization • Insufficient Modularization Hierarchy smells: • Broken Hierarchy • Cyclic Hierarchy • Deep Hierarchy • Missing Hierarchy • Multipath Hierarchy • Rebellious Hierarchy • Unfactored Hierarchy • Wide Hierarchy
- 8. Detected implementation smells • Complex Conditional • Complex Method • Duplicate Code • Empty Catch Block • Long Identifier • Long Method • Long Parameter List • Long Statement • Magic Number • Missing Default • Virtual Method Call from Constructor
- 9. Mining GitHub C# repositories Repositories 1,988 Number of types 436,832 Number of methods 2,265,971 Lines of Code (C#) 49,303,314 Median LOC 4,391
- 10. RQ1. Frequency of smells
- 11. RQ1. What is the distribution of design and implementation smells in C# code? Unutilized Abstraction 90,786 Duplicate Abstraction 73,992 Unnecessary Abstraction 44,583 Imperative Abstraction 11,790 Multifaceted Abstraction 1,236 Deficient Encapsulation 30,214 Unexploited Encapsulation 6,964 Cyclically-dependent Modularization 52,436 Insufficient Modularization 26,429 Broken Modularization 15,624 Hub-like Modularization 676 Unfactored Hierarchy 20,962 Broken Hierarchy 20,332 Rebellious Hierarchy 11,794 Cyclic Hierarchy 4,342 Wide Hierarchy 3,140 Missing Hierarchy 2,598 Multipath Hierarchy 1,454 Deep Hierarchy 179
- 12. RQ1. What is the distribution of design and implementation smells in C# code? Unutilized Abstraction 90,786 Duplicate Abstraction 73,992 Unnecessary Abstraction 44,583 Imperative Abstraction 11,790 Multifaceted Abstraction 1,236 Deficient Encapsulation 30,214 Unexploited Encapsulation 6,964 Cyclically-dependent Modularization 52,436 Insufficient Modularization 26,429 Broken Modularization 15,624 Hub-like Modularization 676 Unfactored Hierarchy 20,962 Broken Hierarchy 20,332 Rebellious Hierarchy 11,794 Cyclic Hierarchy 4,342 Wide Hierarchy 3,140 Missing Hierarchy 2,598 Multipath Hierarchy 1,454 Deep Hierarchy 179
- 13. RQ1. What is the distribution of design and implementation smells in C# code? Magic Number 2,993,353 Long Statement 462,491 Complex Method 95,244 Long Parameter List 79,899 Missing Default 23,497 Complex Conditional 21,643 Duplicate Code 17,921 Long Method 17,521 Empty Catch Block 14,560 Long Identifier 7,741 Virtual Method Call from Constructor 4,545
- 14. RQ1. What is the distribution of design and implementation smells in C# code? Magic Number 2,993,353 Long Statement 462,491 Complex Method 95,244 Long Parameter List 79,899 Missing Default 23,497 Complex Conditional 21,643 Duplicate Code 17,921 Long Method 17,521 Empty Catch Block 14,560 Long Identifier 7,741 Virtual Method Call from Constructor 4,545 On average, one magic number smell per 16 lines of code!!
- 16. RQ2. What is the relationship between the occurrence of design smells and implementation smells? 0 5 10 15 20 0 2 4 6 8 10 12 Design Smells ImplementationSmells 1 8 15 22 30 37 44 51 58 65 72 79 86 94 101 108 115 Counts Co-occurrence between smell instances ⍴ = 0.78 (p-value < 2.2e-16) Co-occurrence between smell types ⍴ = 0.80 (p-value < 2.2e-16) The results emphasize the need to pay attention to smells at all granularities.0 50 100 150 200 250 300 02004006008001000 Design Smells Implementationsmells
- 18. RQ3. Is the principle of coexistence applicable to smells in C# projects? 𝐶 𝑠1, 𝑠2 = 𝑛1 ∗ 𝑛2 𝑁
- 19. RQ4. Smell density and project size
- 20. RQ4. Does smell density depend on the size of the C# repository? 0 50000 100000 150000 200000 020406080100 LOC DesignSmellsDensity 0 50000 100000 150000 200000 0100200300400500 LOC ImplementationSmellsDensity ⍴ = -0.25 (p-value < 2.2e-16) ⍴ = 0.27 (p-value < 2.2e-16)
- 21. Each C# class that you work with, on average, has approximately • 2 design smells (113*14.7/1000 = 1.67) and • 6 implementation smells (113*55.8/1000 = 6.2)