Branch in Time

Full talk: https://tekin.co.uk/2019/02/a-talk-about-revision-histories

In one timeline a quick path to clarity. In the other a painful journey trying to uncover the obscure intent of a line of code. The only difference between these two realities? The revision history…

This is a story about revision histories and their impact on software maintainability. Think Sliding Doors, but with more Git!

Transcript

1. Branch in Time
   A story about revision histories
   @tekin
   

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2. Docs-R-Us
   Seema
   

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3. Seema Docs-R-Us
   

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4. class PatientsController < ApplicationController
   before_action :load_doctor
   def index
   @patients = sorted_patients
   end
   def show
   @patient = @doctor.patients.find(params[:id])
   end
   private
   def sorted_patients
   @doctor.patients.sort { |patient| patient.name }
   end
   def load_doctor
   @doctor = doctor_from_current_session
   

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5. class PatientsController < ApplicationController
   before_action :load_doctor
   def index
   @patients = sorted_patients
   end
   def show
   @patient = @doctor.patients.find(params[:id])
   end
   private
   def sorted_patients
   @doctor.patients.sort { |patient| patient.name }
   end
   def load_doctor
   @doctor = doctor_from_current_session
   

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6. class PatientsController < ApplicationController
   before_action :load_doctor
   def index
   @patients = sorted_patients
   end
   def show
   @patient = @doctor.patients.find(params[:id])
   end
   private
   def sorted_patients
   @doctor.patients.order(:name)
   end
   def load_doctor
   @doctor = doctor_from_current_session
   

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7. class PatientsController < ApplicationController
   before_action :load_doctor
   def index
   @patients = sorted_patients
   end
   def show
   @patient = @doctor.patients.find(params[:id])
   end
   private
   def sorted_patients
   @doctor.patients.order(:name)
   end
   def load_doctor
   @doctor = doctor_from_current_session
   $ rake
   Run options: --seed 45260
   # Running:
   ....................................................................
   ....................................................................
   ....................................................................
   ....................................
   Finished in 123.299088s, 23.8629 runs/s, 34.6397 assertions/s.
   3311 runs, 45124 assertions, 0 failures, 0 errors, 0 skips
   

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8. class Patient < ApplicationRecord
   has_many :appointments
   validates_presence_of :name, :address, :date_of_birth
   end
   class Doctor < ApplicationRecord
   has_many :appointments
   has_many :patients, through: :appointments
   belongs_to :practice
   validates_presence_of :name, :practice
   end
   

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9. Git Fu
   1. git blame
   

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10. $ git blame app/controllers/patients_controller.rb
    Git Fu: git blame
    

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11. 3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 1) # Controller for listing a doctor's pa
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 2) class PatientsController < Application
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 3) before_filter :load_doctor
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 4)
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 5) def index
    6047246d (Josie P 2010-10-29 09:32:25 +0100 6) @patients = sorted_patients
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 7) end
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 8)
    9598514f (Josie P 2010-06-28 17:03:21 +0100 9) def show
    9598514f (Josie P 2010-06-28 17:03:21 +0100 10) @patient = @doctor.patients.find(p
    9598514f (Josie P 2010-06-28 17:03:21 +0100 11) end
    9598514f (Richard E 2010-06-28 17:03:21 +0100 12)
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 13) private
    dbdd0fb9 (Josie P 2010-10-29 09:31:52 +0100 18)
    6047246d (Josie P 2010-10-29 09:32:25 +0100 19) def sorted_patients
    dbdd0fb9 (Josie P 2010-10-29 09:31:52 +0100 20) @doctor.patients.sort {|patient| p
    dbdd0f69 (Josie P 2010-10-29 09:31:52 +0100 21) end
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 14)
    $ git blame app/controllers/patients_controller.rb
    Git Fu: git blame
    

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12. --patch
    Git Fu: git blame
    $ git log dbdd0fb9
    

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13. $ git log dbdd0fb9 --patch
    commit dbdd0fb9e870b91e6925903553f07df3becc9414
    Author: Josie Pickford
    Date: Fri Oct 29 09:31:52 2010 +0100
    PR Feedback: Fixed a typo
    diff --git a/app/controllers/patients_controller.rb b/app/controllers/patients_controller
    index d7c6df5..1e3debb 100644
    --- a/app/controllers/patients_controller.rb
    +++ b/app/controllers/patients_controller.rb
    @@ -13,7 +13,7 @@ class PatientsController < ApplicationController
    private
    def sorted_patients
    - @doctor.patients.sort {|pateint| pateint.name }
    + @doctor.patients.sort {|patient| patient.name }
    end
    Git Fu: git blame
    

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14. Git Fu
    1. git blame
    2. git log -S (AKA The Pickaxe)
    

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15. Git Fu: git log -S (AKA The Pickaxe)
    $ git log -S "sorted_patients" --patch --reverse
    

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16. Git Fu: git log -S (AKA The Pickaxe)
    $ git log -S "sorted_patients" --patch --reverse
    commit 23b6e0c6a9a7a392c312d4f0c51153e0769ebffc
    Author: Josie Pickford
    Date: Thurs Oct 28 17:55:32 2010 +0100
    Rename method
    diff --git a/app/controllers/patients_controller.rb b/app/controllers/
    patients_controller.rb
    index 51fbd8a..d7c6df5 100644
    --- a/app/controllers/patients_controller.rb
    +++ b/app/controllers/patients_controller.rb
    @@ -3,7 +3,7 @@ class PatientsController < ApplicationController
    before_filter :load_doctor
    def index
    - @patients = load_patients
    + @patients = sorted_patients
    end
    

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17. Git Fu
    1. git blame
    2. git log -S (AKA The Pickaxe)
    3. Pickaxe Round 2
    

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18. Git Fu: Pickaxe Round 2
    $ git log -S "load_patients" --patch --reverse
    commit 66f95816017b1c6582034d074333fa18884ad3c3
    Author: Josie Pickford
    Date: Thurs Oct 28 17:00:43 2010 +0100
    Fix patient ordering bug
    diff --git a/app/controllers/patients_controller.rb b/app/controllers/patients_controller
    index cb0e69c..51fbd8a 100644
    --- a/app/controllers/patients_controller.rb
    +++ b/app/controllers/patients_controller.rb
    @@ -3,7 +3,7 @@ class PatientsController < ApplicationController
    before_filter :load_doctor
    def index
    - @patients = @doctor.patients.order(:name)
    + @patients = load_patients
    end
    

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19. Git Fu
    1. git blame
    2. git log -S (AKA The Pickaxe)
    3. Pickaxe Round 2
    4. Find the Pull Request
    

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20. Git Fu: Find the Pull Request
    

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21. Git Fu: Find the Pull Request
    

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22. Git Fu: Find the Pull Request
    

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23. Git Fu: Find the Pull Request
    

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25. 8 years ago...
    

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26. Docs-R-Us
    Josie
    8 years ago...
    

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27. Doh!
    ☕
    8 years ago...
    Josie
    

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28. Y U NO ALPHABETICAL!?
    

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29. class PatientsController < ApplicationController
    before_filter :load_doctor
    def index
    @patients = @doctor.patients.order(:name)
    end
    def show
    @patient = @doctor.patients.find(params[:id])
    end
    private
    def load_doctor
    @doctor = doctor_from_current_session
    end
    end
    

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30. class PatientsController < ApplicationController
    before_filter :load_doctor
    def index
    @patients = @doctor.patients.order(:name)
    end
    def show
    @patient = @doctor.patients.find(params[:id])
    end
    private
    def load_doctor
    @doctor = doctor_from_current_session
    end
    end
    

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31. class Doctor < ApplicationRecord
    has_many :appointments, order: :appointment_date
    has_many :patients, through: :appointments
    belongs_to :practice
    validates_presence_of :name, :practice
    end
    

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32. class Doctor < ApplicationRecord
    has_many :appointments, order: :appointment_date
    has_many :patients, through: :appointments
    belongs_to :practice
    validates_presence_of :name, :practice
    end
    

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33. class Doctor < ApplicationRecord
    has_many :appointments, order: :appointment_date
    has_many :patients, through: :appointments
    belongs_to :practice
    validates_presence_of :name, :practice
    end
    doctor.patients.order(:name)
    Patients Load (1.0ms) SELECT "patients".* FROM "patients"
    INNER JOIN "appointments" ON "patients"."id" = "appointments"."patient_id"
    WHERE “appointments"."doctor_id" = $1
    ORDER BY “appointments"."appointment_date" ASC, "patients"."name" ASC
    irb(main):003:0>
    

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34. class Doctor < ApplicationRecord
    has_many :appointments
    has_many :patients, through: :appointments
    belongs_to :practice
    validates_presence_of :name, :practice
    end
    , order: :appointment_date
    

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35. class Doctor < ApplicationRecord
    has_many :appointments
    has_many :patients, through: :appointments
    belongs_to :practice
    validates_presence_of :name, :practice
    end
    $ rake
    Run options: --seed 45260
    # Running:
    .....F..........FFFF.........F..........FF..............FFFFFFFFF...
    ..............FFFFFFFFFFFFFFFFFF............................FFFF
    Finished in 1.273019s, 24.3516 runs/s, 35.3490 assertions/s.
    

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36. class PatientsController < ApplicationController
    before_filter :load_doctor
    def index
    @patients = @doctor.patients.order(:name)
    end
    def show
    @patient = @doctor.patients.find(params[:id])
    end
    private
    def load_doctor
    @doctor = doctor_from_current_session
    end
    end
    

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37. class PatientsController < ApplicationController
    before_filter :load_doctor
    def index
    @patients =
    end
    def show
    @patient = @doctor.patients.find(params[:id])
    end
    private
    def load_patients
    @doctor.patients.sort { |pateint| pateint.name }
    end
    def load_doctor
    @doctor = doctor_from_current_session
    load_patients
    

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38. Branch history
    

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39. Pull Request (YOLO)
    

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40. Build broke...
    

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41. Build broke...
    

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42. Just one more commit...
    

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43. ... and another
    

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44. Ship it!
    

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45. Intermission
    

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46. Intermission
    

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47. No reorder( ) in Rails 2.3.8
    Intermission
    

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48. 8 years ago...
    

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49. Docs-R-Us
    8 years ago...
    Josie
    

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50. Damn fine coffee!
    8 years ago...
    ☕
    Josie
    

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51. Y U NO ALPHABETICAL!?
    

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52. Branch history
    

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53. Branch history
    

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54. Branch history
    

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55. Git Fu
    1. git rebase --interactive
    

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56. git rebase --interactive head~3
    Git Fu: git rebase --interactive
    $
    

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57. git rebase --interactive head~3
    Git Fu: git rebase --interactive
    $
    

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58. git rebase --interactive head~3
    Git Fu: git rebase --interactive
    $
    

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59. Git Fu: git rebase --interactive
    git rebase --interactive head~3
    $
    

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60. Pull Request
    

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61. Build broke...
    

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62. Fix the build
    git add test/integration
    $
    $
    [fix-patient-order-bug ee74d2f] Fix patient ordering bug
    Date: Fri Oct 29 09:36:08 2010 +0100
    3 files changed, 44 insertions(+), 3 deletion(-)
    $
    git commit --amend --no-edit
    

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63. Fix the build
    git push --force-with-lease
    git add test/integration
    $
    $
    [fix-patient-order-bug ee74d2f] Fix patient ordering bug
    Date: Fri Oct 29 09:36:08 2010 +0100
    3 files changed, 44 insertions(+), 3 deletion(-)
    $
    git commit --amend --no-edit
    

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64. Ship it!
    

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65. Back to the
    future...
    

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66. Docs-R-Us
    Seema
    Seema
    

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67. class PatientsController < ApplicationController
    before_action :load_doctor
    def index
    @patients = sorted_patients
    end
    def show
    @patient = @doctor.patients.find(params[:id])
    end
    private
    def sorted_patients
    @doctor.patients.sort { |patient| patient.name }
    end
    def load_doctor
    @doctor = doctor_from_current_session
    

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68. 3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 1) # Controller for listing a doctor's pa
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 2) class PatientsController < Application
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 3) before_filter :load_doctor
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 4)
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 5) def index
    6047246d (Josie P 2010-10-29 09:32:25 +0100 6) @patients = sorted_patients
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 7) end
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 8)
    9598514f (Josie P 2010-06-28 17:03:21 +0100 9) def show
    9598514f (Josie P 2010-06-28 17:03:21 +0100 10) @patient = @doctor.patients.find(p
    9598514f (Josie P 2010-06-28 17:03:21 +0100 11) end
    9598514f (Richard E 2010-06-28 17:03:21 +0100 12)
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 13) private
    dbdd0fb9 (Josie P 2010-10-29 09:31:52 +0100 18)
    6047246d (Josie P 2010-10-29 09:32:25 +0100 19) def sorted_patients
    33ec144e (Josie P 2010-10-29 09:31:52 +0100 20) @doctor.patients.sort {|patient| p
    dbdd0f69 (Josie P 2010-10-29 09:31:52 +0100 21) end
    3fc122c2 (Richard E 2010-06-28 17:02:54 +0100 14)
    $ git blame app/controllers/patients_controller.rb
    Git Fu: git blame
    

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69. $ git log 33ec144e --patch
    commit 33ec144e70b91e6925903553f07df3becc9414
    Author: Josie Pickford
    Date: Friday Oct 29 09:44:49 2010 +0100
    Fix patient ordering bug
    The patients association is returning patients in appointment date
    order, even when called with an explicit `order(:name)` scope. This is
    because the patients association is a has_many :through the appointments
    association, which has a default order by appointment_date. This causes
    any queries on the association to always sort first by appointment date:
    ORDER BY “appointments"."appointment_date" ASC, "patients"."name" ASC)
    Removing the default ordering from the appointments association is going
    to take a bit of unpicking. To get the bug resolved in the meantime we
    can re-sort the patient records after they've been loaded. Separate
    work has been planned to remove the default ordering altogether.
    Git Fu: git blame
    

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70. class Doctor < ApplicationRecord
    has_many :appointments
    has_many :patients, through: :appointments
    belongs_to :practice
    validates_presence_of :name, :practice
    end
    

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72. • Naming things
    • Automated tests
    • Abstractions
    • Refactoring
    

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73. Your software
    is more than
    the code
    

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75. Programming as
    Theory Building
    Peter Naur
    

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76. Revision History as
    Theory Capturing
    

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79. View Slide

80. Git Fu
    1. Configure an environment for good commit
    messages
    

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81. Configure an environment for good commit messages
    $ git commit -m "Did a thing"
    

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82. Configure an environment for good commit messages
    $ git config --global core.editor “subl -w”
    

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83. Configure an environment for good commit messages
    $ git config --global commit.verbose true
    

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84. Git Fu
    1. Configure an environment for good commit
    messages
    2. Capture the why, not the what
    

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85. Capture the why, not the what
    

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86. Git Fu
    1. Configure an environment for good commit
    messages
    2. Capture the why, not the what
    3. Shape each commit
    

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87. Shape each commit
    • Create small atomic commits
    • Shape as you go, not at the end
    • $ git add --patch / -p
    

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88. Shape each commit
    dd3b43c Refactor Foo
    44b4bd8 Add Bar to Foo
    

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89. Git Fu
    1. Configure an environment for good commit
    messages
    2. Capture the why, not the what
    4. Treat (local) commits as mutable
    3. Shape each commit
    

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90. Treat (local) commits as mutable
    • $ git commit --amend
    • $ git rebase --interactive
    • $ git rebase --abort
    • --fixup / --autosquash
    

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91. Git Fu
    1. Configure an environment for good commit
    messages
    2. Capture the why, not the what
    5. Build your instincts; search your histories
    4. Treat (local) commits as mutable
    3. Shape each commit
    

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92. Build your instincts; search your histories
    • $ git blame file.rb
    • $ git log -S "some_code"
    • $ git annotate file.rb
    

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93. Git Fu
    1. Configure an environment for good commit
    messages
    2. Capture the why, not the what
    5. Treat (local) commits as mutable
    4. Build your instincts; search your histories
    3. Shape each commit
    

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94. tekin.co.uk
    

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96. View Slide

97. Thanks for the Git Fu
    @dgheath21
    @angelajtodd
    @grahamashton
    

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98. Help each
    other Git
    Better
    

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99. Seema Memoji
    Josie Memoji
    Created by
    Inspiration for the story-based approach
    Talk Feedback and Advice
    Slide Advisor
    Git Fu Indent
    Hospital Icon
    Winding Road Photo
    Sound Effects
    TEKIN SULEYMAN
    TEKIN SULEYMAN
    TEKIN SULEYMAN
    NADIA ODUNAYO
    ANDY CROLL
    ANGELA TODD
    GRAHAM ASHTON
    MURRAY STEELE
    NADIA ODUNAYO
    KATRINA OWEN
    BRUCE LEE, ENTER THE DRAGON (1972)
    FLATICON.COM
    JESSE BOWSER ON UNSPLASH
    LEGEND OF ZELDA, A LINK TO THE PAST
    Cast
    

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100. Branch in Time
     A story about revision histories
     @tekin
     

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