David Chelimsky, RubyConf 2010: Maintaining balance while reducing duplication

Slide source: http://web.archive.org/web/20101218001604/http://blog.davidchelimsky.net/2010/11/13/rubyconf-slides-2/

These slides: adapted by me to highlight my favorite DRY anti-example ever

Video: http://www.confreaks.com/videos/434-rubyconf2010-maintaining-balance-while-reducing-duplication

Transcript

1. Maintaining balance while reducing duplication David Chelimsky Saturday, November 13, 2010
2. This talk is about duplication About duplication, is this talk Saturday, November 13, 2010
3. Duplication is bad Saturday, November 13, 2010
4. Code smell: Duplicated Code Saturday, November 13, 2010
5. “Duplicate code is the root of all evil in software design.” Saturday, November 13, 2010
6. Don’t Repeat Yourself The DRY principle Saturday, November 13, 2010
7. You keep using that word ... Saturday, November 13, 2010
8. Every piece of knowledge must have a single, unambiguous, authoritative representation within a system Saturday, November 13, 2010
9. Every piece of knowledge must have a single, unambiguous, authoritative representation within a system Saturday, November 13, 2010
10. Every piece of knowledge must have a single, unambiguous, authoritative representation within a system Saturday, November 13, 2010
11. ALLOCATIONS_ON_DATE = "allocations/{sourceType}/on/{year}/{month}" CREATE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" DELETE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}" Saturday, November 13, 2010
12. "allocations/{sourceType}/on/{year}/{month}" "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}" Saturday, November 13, 2010
13. ALLOCATIONS = "allocations" ALLOCATIONS_ON_DATE = ALLOCATIONS + "/{sourceType}/on/{year}/{month}" CREATE_ALLOCATION = ALLOCATIONS + "/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" DELETE_ALLOCATION = ALLOCATIONS + "/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}" Saturday, November 13, 2010
14. ALLOCATIONS = "allocations" SOURCE_TYPE = "/{sourceType}" ALLOCATIONS_ON_DATE = ALLOCATIONS + SOURCE_TYPE + "/on/{year}/{month}" CREATE_ALLOCATION = ALLOCATIONS + SOURCE_TYPE + "/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" DELETE_ALLOCATION = ALLOCATIONS + SOURCE_TYPE + "/{sourceId}/{targetType}/{targetId}/{year}/{month}" Saturday, November 13, 2010
15. ALLOCATIONS = "allocations" SOURCE_TYPE = "/{sourceType}" SOURCE_ID = "/{sourceId}" TARGET_TYPE = "/{targetType}" TARGET_ID = "/{targetId}" EFFECTIVE_DATE = "/{year}/{month}" ALLOCATIONS_ON_DATE = ALLOCATIONS + SOURCE_TYPE + "/on" + EFFECTIVE_DATE CREATE_ALLOCATION = ALLOCATIONS + SOURCE_TYPE + SOURCE_ID + TARGET_TYPE + TARGET_ID + EFFECTIVE_DATE + "/{percentage}" DELETE_ALLOCATION = ALLOCATIONS + SOURCE_TYPE + SOURCE_ID + TARGET_TYPE + TARGET_ID + EFFECTIVE_DATE Saturday, November 13, 2010
16. DELIMITERS = %w[/ { }] ALLOCATIONS = "allocations" EFFECTIVE_DATE = DELIMITERS[0..1].join + "year" + DELIMITERS[2] + DELIMITERS[0..1].join + "month" + DELIMITERS[2] SOURCE = "source" TARGET = "target" ID = "Id" TYPE = "Type" SOURCE_TYPE = DELIMITERS[0..1].join + SOURCE + TYPE + DELIMITERS[2] SOURCE_ID = DELIMITERS[0..1].join + SOURCE + ID + DELIMITERS[2] TARGET_TYPE = DELIMITERS[0..1].join + TARGET + TYPE + DELIMITERS[2] TARGET_ID = DELIMITERS[0..1].join + TARGET + ID + DELIMITERS[2] ALLOCATION_SOURCE = SOURCE_TYPE + SOURCE_ID ALLOCATION_TARGET = TARGET_TYPE + TARGET_ID ALLOCATIONS_ON_DATE = ALLOCATIONS + SOURCE_TYPE + DELIMITERS[0] + "on" + EFFECTIVE_DATE CREATE_ALLOCATION = ALLOCATIONS + ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE + DELIMITERS[0..1].join + "percentage" + DELIMITERS[2] DELETE_ALLOCATION = ALLOCATIONS + ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE Saturday, November 13, 2010
17. def token(string) "/{#{string}}" end def allocation_path(path) "allocations#{path}" end EFFECTIVE_DATE = token("year") + token("month") SOURCE = "source" TARGET = "target" ID = "Id" TYPE = "Type" SOURCE_TYPE = token(SOURCE + TYPE) SOURCE_ID = token(SOURCE + ID) TARGET_TYPE = token(TARGET + TYPE) TARGET_ID = token(TARGET + ID) ALLOCATION_SOURCE = SOURCE_TYPE + SOURCE_ID ALLOCATION_TARGET = TARGET_TYPE + TARGET_ID ALLOCATIONS_ON_DATE = allocation_path(SOURCE_TYPE + "/on" + EFFECTIVE_DATE) CREATE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE + token("percentage") ) DELETE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE ) Saturday, November 13, 2010
18. "/allocations/developer/37/project/2010/10/42" def token(string) "/{#{string}}" end def allocation_path(path) "allocations#{path}" end EFFECTIVE_DATE = token("year") + token("month") SOURCE = "source" TARGET = "target" ID = "Id" TYPE = "Type" SOURCE_TYPE = token(SOURCE + TYPE) SOURCE_ID = token(SOURCE + ID) TARGET_TYPE = token(TARGET + TYPE) TARGET_ID = token(TARGET + ID) ALLOCATION_SOURCE = SOURCE_TYPE + SOURCE_ID ALLOCATION_TARGET = TARGET_TYPE + TARGET_ID ALLOCATIONS_ON_DATE = allocation_path(SOURCE_TYPE + "/on" + EFFECTIVE_DATE) CREATE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE + token("percentage") ) DELETE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE ) Saturday, November 13, 2010
19. "/allocations/developer/37/project/2010/10/42" ALLOCATIONS_ON_DATE = "allocations/{sourceType}/on/{year}/{month}" CREATE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" DELETE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}" "allocations/{sourceType}/on/{year}/{month}" "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}" Saturday, November 13, 2010
20. def token(string) "/{#{string}}" end def allocation_path(path) "allocations#{path}" end EFFECTIVE_DATE = token("year") + token("month") SOURCE = "source" TARGET = "target" ID = "Id" TYPE = "Type" SOURCE_TYPE = token(SOURCE + TYPE) SOURCE_ID = token(SOURCE + ID) TARGET_TYPE = token(TARGET + TYPE) TARGET_ID = token(TARGET + ID) ALLOCATION_SOURCE = SOURCE_TYPE + SOURCE_ID ALLOCATION_TARGET = TARGET_TYPE + TARGET_ID ALLOCATIONS_ON_DATE = allocation_path( SOURCE_TYPE + "/on" + EFFECTIVE_DATE ) CREATE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE + token("percentage") ) DELETE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE ) ALLOCATIONS_ON_DATE = "allocations/{sourceType}/on/{year}/{month}" CREATE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" DELETE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}" Saturday, November 13, 2010
21. def token(string) "/{#{string}}" end def allocation_path(path) "allocations#{path}" end EFFECTIVE_DATE = token("year") + token("month") SOURCE = "source" TARGET = "target" ID = "Id" TYPE = "Type" SOURCE_TYPE = token(SOURCE + TYPE) SOURCE_ID = token(SOURCE + ID) TARGET_TYPE = token(TARGET + TYPE) TARGET_ID = token(TARGET + ID) ALLOCATION_SOURCE = SOURCE_TYPE + SOURCE_ID ALLOCATION_TARGET = TARGET_TYPE + TARGET_ID ALLOCATIONS_ON_DATE = allocation_path( SOURCE_TYPE + "/on" + EFFECTIVE_DATE ) CREATE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE + token("percentage") ) DELETE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE ) ALLOCATIONS_ON_DATE = "allocations/{sourceType}/on/{year}/{month}" CREATE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" DELETE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}" some duplicate letters/words Saturday, November 13, 2010
22. def token(string) "/{#{string}}" end def allocation_path(path) "allocations#{path}" end EFFECTIVE_DATE = token("year") + token("month") SOURCE = "source" TARGET = "target" ID = "Id" TYPE = "Type" SOURCE_TYPE = token(SOURCE + TYPE) SOURCE_ID = token(SOURCE + ID) TARGET_TYPE = token(TARGET + TYPE) TARGET_ID = token(TARGET + ID) ALLOCATION_SOURCE = SOURCE_TYPE + SOURCE_ID ALLOCATION_TARGET = TARGET_TYPE + TARGET_ID ALLOCATIONS_ON_DATE = allocation_path( SOURCE_TYPE + "/on" + EFFECTIVE_DATE ) CREATE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE + token("percentage") ) DELETE_ALLOCATION = allocation_path( ALLOCATION_SOURCE + ALLOCATION_TARGET + EFFECTIVE_DATE ) ALLOCATIONS_ON_DATE = "allocations/{sourceType}/on/{year}/{month}" CREATE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}/{percentage}" DELETE_ALLOCATION = "allocations/{sourceType}/{sourceId}/{targetType}/{targetId}/{year}/{month}" some duplicate letters/words #!(*&?$@ Saturday, November 13, 2010
23. DRY does not mean “don’t type the same characters twice” Saturday, November 13, 2010
24. DRY is about duplicated concepts Saturday, November 13, 2010
25. every time you reduce duplication you increase coupling by introducing new dependencies Saturday, November 13, 2010
26. it is important to depend on the right things Saturday, November 13, 2010
27. DRY is about isolation of change Saturday, November 13, 2010
28. depend on things which are less likely to change Saturday, November 13, 2010
29. The Dependency Inversion Principle depend on abstractions Saturday, November 13, 2010
30. in Ruby, almost everything is an abstraction Saturday, November 13, 2010
31. How do I know if this particular duplication is problematic? Saturday, November 13, 2010
32. Purpose/Intention Saturday, November 13, 2010
33. Risk Saturday, November 13, 2010
34. Have to change in more than one place? Saturday, November 13, 2010
35. Might forget to change in other place! Saturday, November 13, 2010
36. Duplication is not always obvious Saturday, November 13, 2010
37. Same name, different meaning Saturday, November 13, 2010
38. Less duplication can mean more indirection Saturday, November 13, 2010
39. this can make it harder to reason about code Saturday, November 13, 2010
40. Metaprogramming is helpful when you can’t know the runtime conditions Saturday, November 13, 2010
41. Metaprogramming can also make it harder to reason about code Saturday, November 13, 2010
42. Many problems in software can be traced back to duplication, but ... Saturday, November 13, 2010
43. ... not all duplication is inherently evil Saturday, November 13, 2010
44. Duplication comes in many forms Saturday, November 13, 2010
45. Duplication appears for several reasons Saturday, November 13, 2010
46. Every piece of knowledge must have a single, unambiguous, authoritative representation within a system Saturday, November 13, 2010
47. This is not really about duplicated strings of characters Saturday, November 13, 2010
48. DRY is about duplicated concepts Saturday, November 13, 2010
49. every time you reduce duplication you increase coupling by introducing new dependencies Saturday, November 13, 2010
50. depend on things which are less likely to change Saturday, November 13, 2010
51. learn about code smells Saturday, November 13, 2010
52. Duplicated Code Feature Envy Inappropriate Intimacy Large Class Long Method Saturday, November 13, 2010
53. learn more principles! Saturday, November 13, 2010
54. •Single Responsibility •Open/Closed •Liskov Substitution •Interface Segregation •Dependency Inversion SOLID Principles Saturday, November 13, 2010
55. OO in one sentence keep it shy, DRY, and tell the other guy! Saturday, November 13, 2010