Working on a Legacy App

Transcript

1. Hi
   

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2. Marco Sero
   @marcosero
   

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3. Microsoft
   

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4. iOS @ Yammer
   

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5. WORKING ON A
   LEGACY APP
   

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6. DEFINITION OF
   LEGACY
   

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7. "Anything handed down
   from the past, as from an
   ancestor or predecessor"
   

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8. "Obsolete"
   

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9. DEFINITION OF
   LEGACY CODE
   

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10. No Unit Tests
    

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11. Still used in
    Production
    

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12. IT JUST
    WORKS*
    *most of the time
    

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13. Written in a language
    that you don't
    typically do new
    development in
    

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14. Swift 1.2
    

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15. Old and complicated
    History
    

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16. Many
    Contributors...
    

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17. ...That have all quit
    

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18. Let's recap
    ✔ Still used in production !
    ✔ Old or deprecated language !
    ✔ Without unit tests !
    ✔ Old history with many, many contributors... !
    ✔ ...most of which not around anymore !
    

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19. Or whenever
    you feel like this
    

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20. Not much
    Legacy
    on iOS
    

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21. iOS development is new(ish)
    Short app lifetime
    Easier to re-write
    

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22. So why bother?
    

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25. JUST
    STOP
    PLEASE
    STOP
    

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26. WHERE DO I
    START?
    

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27. STATS
    

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28. Identify the risk and start there
    $ find YourApp -iname "*.h" |
    xargs grep -h 'interface' |
    cut -d ' ' -f 2 |
    while read class;
    do echo `grep -r "\b$class\b" YourApp --include "*.m" | wc -l` $class;
    done |
    sort -n -u
    from Destroy All Software screencasts.
    

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30. Leverage
    git
    

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31. Git Blame
    ⌥⌘⇧㾑
    

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35. git log -L 1,1:/your/file
    

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36. COMMIT MESSAGES
    

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39. Your
    COMMIT MESSAGES
    are your
    LEGACY
    

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40. (Maybe) DEAD
    CODE
    

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41. TOMBSTONES
    - (void)possibleDeadCode
    {
    // current date when tombstone was added
    log_tombstone(@"2015-08-21");
    }
    • Log found?
    ➡ Code is alive !
    • Log not found?
    ➡ Code is dead "
    From David Schnepper's Ignite talk, "Isn't
    That Code Dead?"
    

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42. CONTINUOUS
    DESTRUCTION
    

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43. Inheritance
    

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45. @implementation RootViewController
    - (void)doSomething:(NSString *)aString { }
    @end
    @implementation RootViewController_iPad
    - (void)doSomething:(NSString *)aString {
    NSLog(@"%@ iPad", aString);
    }
    @end
    @implementation RootViewController_iPhone
    - (void)doSomething:(NSString *)aString {
    NSLog(@"%@ iPhone", aString);
    }
    @end
    RootViewController *vc = [[RootViewController_iPad alloc] init];
    [vc doSomething:@"cool"]; // prints "cool iPad"
    

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46. @implementation RootViewController
    - (void)doSomething:(NSString *)aString { }
    @end
    @implementation RootViewController_iPad
    - (void)doSomething {
    NSLog(@"iPad");
    }
    @end
    @implementation RootViewController_iPhone
    - (void)doSomething:(NSString *)aString {
    NSLog(@"%@ iPhone", aString);
    }
    @end
    RootViewController *vc = [[RootViewController_iPad alloc] init];
    [vc doSomething:@"cool"]; // prints nothing
    

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47. class RootViewController: UIViewController {
    func doSomething(aString: String) { }
    }
    class RootViewController_iPad: RootViewController {
    override func doSomething(aString: String) {
    print(aString + "iPad")
    }
    }
    class RootViewController_iPhone: RootViewController {
    override func doSomething(aString: String) {
    print(aString + "iPhone")
    }
    }
    

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48. class RootViewController: UIViewController {
    func doSomething(aString: String) { }
    }
    class RootViewController_iPad: RootViewController {
    override func doSomething() { // COMPILE ERROR
    print("iPad")
    }
    }
    class RootViewController_iPhone: RootViewController {
    override func doSomething(aString: String) {
    print(aString + "iPhone")
    }
    }
    

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49. "I've got your
    back"
    — Chris Lattner on Swift's Safety
    

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50. THIRD-PARTY
    DEPENDENCIES
    

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51. AVOID
    THEM
    (if possible)
    

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52. Build a small, but non-trivial, Rails app. [...] Go away for six
    months. Come back and update all of your dependencies. Your
    app no longer works.
    — Gary Bernhardt
    

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53. Build a small, but non-trivial, iOS app. [...] Go away for six months.
    Come back and update all of your dependencies. Your app no
    longer works.
    — Marco Sero
    

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54. FORKS
    

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55. Recap:
    • Start identifying the risk
    • Leverage Git
    • Spend some time writing good commit messages
    • Continuous destruction of dead code
    • Avoid subclasses and touch them with care
    • Third party dependencies have a cost and private forks are
    almost always a bad idea
    

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57. BE A GOOD CITIZEN
    

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58. HAVE FUN
    !"#
    

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59. Thank you.
    @marcosero
    • Working Effectively with Legacy Code by Michael Feathers
    • Utter Disregard for Git Commit History by Zach Holman
    http://zachholman.com/posts/git-commit-history/
    • Destroy All Software screencast by Gary Bernhardt
    https://www.destroyallsoftware.com/screencasts
    • Isn't That Code Dead? by David Schnepper
    https://www.youtube.com/watch?v=29UXzfQWOhQ
    

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