Creating A Better Developer Experience By Avoiding Legacy Code

Presented at the virtual Android Summit 2020.

Transcript

1. Creating A Better Developer
   Experience By Avoiding Legacy
   Code
   Adam McNeilly - @AdamMc331
   @AdamMc331
   #AndroidSummit 1
   

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2. What Is Legacy Code?
   @AdamMc331
   #AndroidSummit 2
   

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3. What Is Legacy Code?
   @AdamMc331
   #AndroidSummit 3
   

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4. What Is Legacy Code?
   1. Code that was written before we knew better.
   @AdamMc331
   #AndroidSummit 3
   

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5. What Is Legacy Code?
   1. Code that was written before we knew better.
   2. Code that was written by someone else, who is no longer a
   maintainer.
   @AdamMc331
   #AndroidSummit 3
   

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6. What Is Legacy Code?
   1. Code that was written before we knew better.
   2. Code that was written by someone else, who is no longer a
   maintainer.
   3. Code that doesn't have tests.
   @AdamMc331
   #AndroidSummit 3
   

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7. What Is Legacy Code?
   1. Code that was written before we knew better.
   2. Code that was written by someone else, who is no longer a
   maintainer.
   3. Code that doesn't have tests.
   4. Code that we're unable to/afraid to change because everything might
   break.
   @AdamMc331
   #AndroidSummit 3
   

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8. What Is Legacy Code?
   1. Code that was written before we knew better.
   2. Code that was written by someone else, who is no longer a
   maintainer.
   3. Code that doesn't have tests.
   4. Code that we're unable to/afraid to change because everything might
   break.
   5. Code without any type of comments or documentation.
   @AdamMc331
   #AndroidSummit 3
   

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9. What Is Legacy Code?
   1. Code that was written before we knew better.
   2. Code that was written by someone else, who is no longer a
   maintainer.
   3. Code that doesn't have tests.
   4. Code that we're unable to/afraid to change because everything might
   break.
   5. Code without any type of comments or documentation.
   6. All of the above!
   @AdamMc331
   #AndroidSummit 3
   

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10. Why Do We Care?
    @AdamMc331
    #AndroidSummit 4
    

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11. Legacy Code Impacts Our Work
    @AdamMc331
    #AndroidSummit 5
    

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12. Legacy Code Impacts Our Work
    1. Legacy code can become a blocker for new development.
    @AdamMc331
    #AndroidSummit 5
    

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13. Legacy Code Impacts Our Work
    1. Legacy code can become a blocker for new development.
    2. Legacy code can prevent us from shipping with confidence.
    @AdamMc331
    #AndroidSummit 5
    

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14. Legacy Code Impacts Our Work
    1. Legacy code can become a blocker for new development.
    2. Legacy code can prevent us from shipping with confidence.
    3. Legacy code can be confusing and difficult to build on top of.
    @AdamMc331
    #AndroidSummit 5
    

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15. Legacy Code Impacts Our Work
    1. Legacy code can become a blocker for new development.
    2. Legacy code can prevent us from shipping with confidence.
    3. Legacy code can be confusing and difficult to build on top of.
    4. Legacy code is not fun to work with for these, and many other
    reasons.
    @AdamMc331
    #AndroidSummit 5
    

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16. Is Legacy Code
    Inevitable?
    @AdamMc331
    #AndroidSummit 6
    

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17. Is Legacy Code Inevitable?
    Code will age with time, and new practices will always arise.
    However, we can examine our own experiences with legacy code
    to help ensure our future selves and teammates have a better
    developer experience.
    @AdamMc331
    #AndroidSummit 7
    

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18. Myth: Legacy Code
    Was Written By
    Someone Else
    @AdamMc331
    #AndroidSummit 8
    

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19. Legacy Code Was Written By
    Someone Else
    @AdamMc331
    #AndroidSummit 9
    

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20. Legacy Code Was Written By
    Someone Else
    » We can't avoid people moving on to new opportunities.
    @AdamMc331
    #AndroidSummit 9
    

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21. Legacy Code Was Written By
    Someone Else
    » We can't avoid people moving on to new opportunities.
    » One day, YOU will be that someone.
    @AdamMc331
    #AndroidSummit 9
    

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22. Legacy Code Was Written By
    Someone Else
    » We can't avoid people moving on to new opportunities.
    » One day, YOU will be that someone.
    » Your past self from one year ago also wrote code like a
    different person.
    @AdamMc331
    #AndroidSummit 9
    

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23. @AdamMc331
    #AndroidSummit 10
    

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24. Exploring Causes Of
    Legacy Code
    @AdamMc331
    #AndroidSummit 11
    

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25. Legacy Code Doesn't
    Have Tests
    @AdamMc331
    #AndroidSummit 12
    

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26. Legacy Code Doesn't Have Tests
    @AdamMc331
    #AndroidSummit 13
    

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27. Legacy Code Doesn't Have Tests
    There are two reasons code doesn't have tests:
    @AdamMc331
    #AndroidSummit 14
    

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28. Legacy Code Doesn't Have Tests
    There are two reasons code doesn't have tests:
    1. The author chose not to write any.
    @AdamMc331
    #AndroidSummit 14
    

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29. Legacy Code Doesn't Have Tests
    There are two reasons code doesn't have tests:
    1. The author chose not to write any.
    2. The code wasn't testable in the first place.
    @AdamMc331
    #AndroidSummit 14
    

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30. Untestable Code
    @AdamMc331
    #AndroidSummit 15
    

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31. Untestable Code
    1. Code with a lot of static references.
    @AdamMc331
    #AndroidSummit 15
    

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32. Untestable Code
    1. Code with a lot of static references.
    2. Code that doesn't leverage proper dependency injection.
    @AdamMc331
    #AndroidSummit 15
    

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33. Untestable Code
    1. Code with a lot of static references.
    2. Code that doesn't leverage proper dependency injection.
    These unclear static dependencies can sometimes indicate fragile
    code that people are afraid to change.
    @AdamMc331
    #AndroidSummit 16
    

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34. Untestable Code
    class ProfileViewModel : ViewModel() {
    private fun loadProfile() {
    try {
    // ...
    } catch (e: Throwable) {
    MyErrorTool.getInstance().logException(e)
    }
    }
    }
    @AdamMc331
    #AndroidSummit 17
    

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35. Untestable Code
    } catch (e: Throwable) {
    MyErrorTool.getInstance().logException(e)
    }
    @AdamMc331
    #AndroidSummit 18
    

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36. Untestable Code
    } catch (e: Throwable) {
    MyErrorTool.getInstance().logException(e)
    }
    » MyErrorTool is difficult to mock for unit tests.
    @AdamMc331
    #AndroidSummit 18
    

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37. Untestable Code
    } catch (e: Throwable) {
    MyErrorTool.getInstance().logException(e)
    }
    » MyErrorTool is difficult to mock for unit tests.
    » We don't want our negative tests to actually log errors to our
    production tool.
    @AdamMc331
    #AndroidSummit 18
    

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38. Untestable Code
    } catch (e: Throwable) {
    MyErrorTool.getInstance().logException(e)
    }
    » MyErrorTool is difficult to mock for unit tests.
    » We don't want our negative tests to actually log errors to our
    production tool.
    » This tool could be running setup that crashes our tests.
    @AdamMc331
    #AndroidSummit 18
    

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39. Untestable Code - Quick Solution
    // Inject error tool with default value.
    class ProfileViewModel(
    private val errorTool: MyErrorTool = MyErrorTool.getInstance()
    ) : ViewModel() {
    private fun loadProfile() {
    try {
    // ...
    } catch (e: Throwable) {
    errorTool.logException(e)
    }
    }
    }
    @AdamMc331
    #AndroidSummit 19
    

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40. Tightly Coupled
    Dependencies Become
    Legacy Code
    @AdamMc331
    #AndroidSummit 20
    

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41. Tightly Coupled Dependencies
    Become Legacy Code
    @AdamMc331
    #AndroidSummit 21
    

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42. Tightly Coupled Dependencies
    Become Legacy Code
    » Companies change third party vendors (analytics trackers,
    error reporters).
    @AdamMc331
    #AndroidSummit 21
    

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43. Tightly Coupled Dependencies
    Become Legacy Code
    » Companies change third party vendors (analytics trackers,
    error reporters).
    » Companies may change tech stacks (REST to GraphQL).
    @AdamMc331
    #AndroidSummit 21
    

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44. Tightly Coupled Dependencies
    Become Legacy Code
    » Companies change third party vendors (analytics trackers,
    error reporters).
    » Companies may change tech stacks (REST to GraphQL).
    » New image loading libraries are made every few years.
    @AdamMc331
    #AndroidSummit 21
    

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45. Tightly Coupled Dependencies
    Become Legacy Code
    » Companies change third party vendors (analytics trackers,
    error reporters).
    » Companies may change tech stacks (REST to GraphQL).
    » New image loading libraries are made every few years.
    » Code that doesn't allow these things to be changed is likely to
    become legacy code.
    @AdamMc331
    #AndroidSummit 21
    

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46. Strict Dependencies
    // Codebase strongly relies on `MyErrorTool`
    class ProfileViewModel(
    private val errorTool: MyErrorTool = MyErrorTool.getInstance()
    ) : ViewModel()
    @AdamMc331
    #AndroidSummit 22
    

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47. Strict Dependencies
    // Codebase strongly relies on `MyErrorTool`
    class ProfileViewModel(
    private val errorTool: MyErrorTool = MyErrorTool.getInstance()
    ) : ViewModel()
    » This class is strictly tied to MyErrorTool method contracts.
    @AdamMc331
    #AndroidSummit 22
    

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48. Strict Dependencies
    // Codebase strongly relies on `MyErrorTool`
    class ProfileViewModel(
    private val errorTool: MyErrorTool = MyErrorTool.getInstance()
    ) : ViewModel()
    » This class is strictly tied to MyErrorTool method contracts.
    » Despite dependency injection, this will make swapping our
    error tool difficult.
    @AdamMc331
    #AndroidSummit 22
    

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49. Wrapping Dependencies
    interface ErrorReporter {
    fun reportError(error: Throwable)
    }
    class FirebaseErrorReporter : ErrorReporter {
    override fun reportError(error: Throwable) {
    Firebase.getInstance().logException(error)
    }
    }
    @AdamMc331
    #AndroidSummit 23
    

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50. Wrapping Dependencies
    // Firebase is default, but we have the ability
    // to pass anything we want here.
    class ProfileViewModel(
    private val errorReporter: ErrorReporter = FirebaseErrorReporter()
    ) : ViewModel()
    @AdamMc331
    #AndroidSummit 24
    

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51. Wrapping Dependencies
    @AdamMc331
    #AndroidSummit 25
    

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52. Wrapping Dependencies
    » Easier to provide fake/mock implementations in tests.
    @AdamMc331
    #AndroidSummit 25
    

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53. Wrapping Dependencies
    » Easier to provide fake/mock implementations in tests.
    » Easier to entirely swap third party tools.
    @AdamMc331
    #AndroidSummit 25
    

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54. Wrapping Dependencies
    » Easier to provide fake/mock implementations in tests.
    » Easier to entirely swap third party tools.
    » Easier to update tools.
    @AdamMc331
    #AndroidSummit 25
    

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55. Wrapping Dependencies
    val coreModule = module {
    /**
    * Change the reporter supplied by your DI manager,
    * the entire app just updates!
    */
    single {
    FirebaseErrorReporter()
    // SentryErrorReporter()
    // EmbraceErrorReporter()
    }
    }
    @AdamMc331
    #AndroidSummit 26
    

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56. Wrapping Dependencies
    class FirebaseErrorReporter : ErrorReporter {
    /**
    * Wrapping this method makes it easy to update our project
    * if the library changes its method signature.
    */
    override fun reportError(error: Throwable) {
    // Firebase.getInstance().logException(error)
    Firebase.getInstance().logError(error)
    }
    }
    @AdamMc331
    #AndroidSummit 27
    

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57. These Steps Avoid A Lot Of
    Legacy Code Pain Points
    @AdamMc331
    #AndroidSummit 28
    

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58. These Steps Avoid A Lot Of
    Legacy Code Pain Points
    » We have testable code that we can ship with confidence.
    @AdamMc331
    #AndroidSummit 28
    

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59. These Steps Avoid A Lot Of
    Legacy Code Pain Points
    » We have testable code that we can ship with confidence.
    » We have decoupled third party tools, giving us freedom to
    swap vendors with ease.
    @AdamMc331
    #AndroidSummit 28
    

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60. These Steps Avoid A Lot Of
    Legacy Code Pain Points
    » We have testable code that we can ship with confidence.
    » We have decoupled third party tools, giving us freedom to
    swap vendors with ease.
    » We can confidently upgrade our third party tools and limit the
    code changes required.
    @AdamMc331
    #AndroidSummit 28
    

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61. Legacy Code Is Code
    No One On The Team
    Understands
    @AdamMc331
    #AndroidSummit 29
    

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62. Legacy Code Is Code
    No One On The Team
    Understands Doesn't
    Have Documentation
    @AdamMc331
    #AndroidSummit 30
    

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63. How Undocumented Code
    Becomes Legacy Code
    @AdamMc331
    #AndroidSummit 31
    

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64. How Undocumented Code
    Becomes Legacy Code
    1. The author of the code understood what they were writing.
    @AdamMc331
    #AndroidSummit 31
    

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65. How Undocumented Code
    Becomes Legacy Code
    1. The author of the code understood what they were writing.
    2. The author felt that the code was self documenting.
    @AdamMc331
    #AndroidSummit 31
    

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66. How Undocumented Code
    Becomes Legacy Code
    1. The author of the code understood what they were writing.
    2. The author felt that the code was self documenting.
    3. The author didn't provide additional context.
    @AdamMc331
    #AndroidSummit 31
    

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67. How Undocumented Code
    Becomes Legacy Code
    1. The author of the code understood what they were writing.
    2. The author felt that the code was self documenting.
    3. The author didn't provide additional context.
    4. The author leaves the team, only for someone else to find this class
    much later.
    @AdamMc331
    #AndroidSummit 31
    

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68. How Undocumented Code
    Becomes Legacy Code
    1. The author of the code understood what they were writing.
    2. The author felt that the code was self documenting.
    3. The author didn't provide additional context.
    4. The author leaves the team, only for someone else to find this class
    much later.
    5. The new team has no idea how this code works, or if it can be changed.
    @AdamMc331
    #AndroidSummit 31
    

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69. Looking After Future
    Developers With
    Documentation
    @AdamMc331
    #AndroidSummit 32
    

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70. Document When You Rely
    External Code Samples
    /**
    * Feature XYZ requires a ViewPager like experience, but
    * without the user being able to control each step. We've
    * implemented a ViewPager that rejects any user interraction.
    *
    * Source: https://stackoverflow.com/a/9650884/3131147
    */
    class NonSwipeableViewPager(
    context: Context,
    attrs: AttributeSet? = null
    ) : ViewPager(context, attrs) {
    }
    @AdamMc331
    #AndroidSummit 33
    

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71. Document When You Rely
    External Code Samples
    /**
    * Feature XYZ requires a ViewPager like experience, but
    * without the user being able to control each step. We've
    * implemented a ViewPager that rejects any user interraction.
    *
    * Source: https://stackoverflow.com/a/9650884/3131147
    */
    class NonSwipeableViewPager(
    context: Context,
    attrs: AttributeSet? = null
    ) : ViewPager(context, attrs) {
    }
    » This allows future devs to understand why this class was added, and explore if there are new first-party solutions.
    @AdamMc331
    #AndroidSummit 33
    

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72. Document When You Work
    Around Library Bugs
    /**
    * Due to github.com/company/library/issues/1234 we needed
    * to implement this work around to prevent a crash on
    * Android devices running API 21.
    */
    private fun doLibraryWorkAround() {
    // ...
    }
    @AdamMc331
    #AndroidSummit 34
    

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73. Document When You Work
    Around Library Bugs
    /**
    * Due to github.com/company/library/issues/1234 we needed
    * to implement this work around to prevent a crash on
    * Android devices running API 21.
    */
    private fun doLibraryWorkAround() {
    // ...
    }
    » This allows future devs to understand what this block of code is doing, and explore if the bug has been fixed
    in a subsequent library update.
    @AdamMc331
    #AndroidSummit 34
    

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74. Document When You Use
    Libraries For Specific Use Cases
    implementation("androidx.security:security-crypto:$rootProject.ext.versions.security") {
    because("This dependency allows us to use EncryptedSharedPreferences to store sensitive information.")
    }
    @AdamMc331
    #AndroidSummit 35
    

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75. Document When You Use
    Libraries For Specific Use Cases
    implementation("androidx.security:security-crypto:$rootProject.ext.versions.security") {
    because("This dependency allows us to use EncryptedSharedPreferences to store sensitive information.")
    }
    » This allows future devs to update version numbers with
    confidence, as well as understanding what to test, and why
    this library was chosen.
    @AdamMc331
    #AndroidSummit 35
    

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76. Why This
    Documentation
    Matters
    @AdamMc331
    #AndroidSummit 36
    

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77. Why This Documentation Matters
    We're not trying to prevent code from becoming obsolete and
    outdated. We're trying to help the future maintainers respond
    accordingly.
    @AdamMc331
    #AndroidSummit 37
    

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78. Recap
    @AdamMc331
    #AndroidSummit 38
    

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79. Recap
    » Writing testable code with decent coverage helps future
    developers refactor with confidence.
    @AdamMc331
    #AndroidSummit 38
    

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80. Recap
    » Writing testable code with decent coverage helps future
    developers refactor with confidence.
    » Wrapping dependencies allows future developers to update
    and replace tooling easily.
    @AdamMc331
    #AndroidSummit 38
    

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81. Recap
    » Writing testable code with decent coverage helps future
    developers refactor with confidence.
    » Wrapping dependencies allows future developers to update
    and replace tooling easily.
    » Documenting certain decisions allows future developers to
    confidently understand, refactor, and replace code written by
    someone else.
    @AdamMc331
    #AndroidSummit 38
    

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82. Remember
    The goal isn't to completely eradicate legacy code. It's to look out
    for our future teammates by not leaving behind rigid, confusing,
    and unmaintainable code.
    @AdamMc331
    #AndroidSummit 39
    

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83. Thanks!
    @AdamMc331
    #AndroidSummit 40
    

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