Micro-clones are tiny duplicated pieces of code; they typically comprise only a few statements or lines. In this paper, we expose the “last line effect,” the phenomenon that the last line or statement in a micro-clone is much more likely to contain an error than the previous lines or statements. We do this by analyzing 208 open source projects and reporting on 202 faulty micro-clones

1. The Last Line Effect
Moritz Beller
@Inventitech
Andy Zaidman
Andrey Karpov

2. TrinityCore Example
Last Line Effect

3. TrinityCore Example
Last Line Effect

4. TrinityCore Example
Last Line Effect

5. Chromium Example
Last Statement Effect

6. Chromium Example
Last Statement Effect

7. Chromium Example
Last Statement Effect

8. Chromium Example
Last Statement Effect

9. Chromium Example
Last Statement Effect

10. Chromium Example

11. Chromium Example

12. Chromium Example

13. Chromium Example

14. Chromium Example

15. Chromium Example

16. Chromium Example
Clone Class

17. Chromium Example
Clone Class
AST-Node1

18. Chromium Example
Clone Class
AST-Node
1
1

19. Chromium Example
Clone Class
AST-Node
1 2
1

20. Chromium Example
Clone Class
AST-Node
1 2 3
1

21. Chromium Example
Clone Class
AST-Node
1 2 3 4
1

22. Chromium Example
Clone Class
AST-Node
1 2 3 4 5
1

23. Chromium Example
Clone Class
AST-Node
1 2 3 4 5
1

24. Chromium Example
Clone Class
AST-Node
1 2 3 4 5
1
Type 2 Clone: “syntactically identical cop[ies]; only variable, type, or
function identifiers have […] changed.” Koschke, 2007.

25. Chromium Example
Clone Class
AST-Node
1 2 3 4 5
1
Type 2 Clone: “syntactically identical cop[ies]; only variable, type, or
function identifiers have […] changed.” Koschke, 2007.
Very Short Type 2-Clone:
Micro-Clone

26. Very Short Clones:
Micro-Clones

27. Shortcut: Identical Subexpressions

28. Shortcut: Identical Subexpressions

29. Shortcut: Identical Subexpressions

30. Shortcut: Identical Subexpressions

31. Shortcut: Identical Subexpressions

32. Shortcut: Identical Subexpressions
Shortcut to Faulty Micro-Clones

34. PVS-Studio

35. PVS-Studio

36. 208 OSS projectsPVS-Studio

37. 208 OSS projectsPVS-Studio

38. 208 OSS projectsPVS-Studio

39. 208 OSS projectsPVS-Studio
202 Faulty Micro-Clones

40. 208 OSS projectsPVS-Studio
202 Faulty Micro-Clones

41. Error Distribution for Micro-Clones
> 1 Line

42. Error Distribution for Micro-Clones
Within 1 Line

43. What We Do Not Know (Yet) ...

44. ●
Why did we find so few faulty micro-clones?
What We Do Not Know (Yet) ...

45. ●
Why did we find so few faulty micro-clones?
What We Do Not Know (Yet) ...

46. ●
Why did we find so few faulty micro-clones?
What We Do Not Know (Yet) ...

47. ●
Why did we find so few faulty micro-clones?
What We Do Not Know (Yet) ...
●
Are faulty micro-clones common among micro-clones?

48. ●
Why did we find so few faulty micro-clones?
What We Do Not Know (Yet) ...
●
Are faulty micro-clones common among micro-clones?

49. ●
Why did we find so few faulty micro-clones?
What We Do Not Know (Yet) ...
●
Are faulty micro-clones common among micro-clones?

50. ●
Why did we find so few faulty micro-clones?
What We Do Not Know (Yet) ...
●
Are faulty micro-clones common among micro-clones?
●
How are micro-clones created and evolved?

51. ●
Why did we find so few faulty micro-clones?
What We Do Not Know (Yet) ...
●
Are faulty micro-clones common among micro-clones?
●
How are micro-clones created and evolved?

52. @Inventitech
Moritz Beller, TU Delft
The Last Line Effect

53. @Inventitech
Moritz Beller, TU Delft
The Last Line Effect

54. @Inventitech
Moritz Beller, TU Delft
The Last Line Effect

55. @Inventitech
Moritz Beller, TU Delft
The Last Line Effect
> code.|