Rules

We're iconoclasts who reject arbitrary constraints yet long for
understandable, predictable, changeable applications. We want code that
follows rules yet we refuse to let rules to get in our way. We're
deeply attached to the little rules that help get things done (No
trailing whitespace! Indent using two spaces!) and despise the big,
complicated ones that impose one-size-fits-all straitjackets on
otherwise sane programming problems.

This talk proposes 5 'little' rules for writing object-oriented code.
These rules are determinedly simple yet produce code that experts love
and novices can be trusted to change; they fill the space between
anarchy and order with practical, common sense. The rules guide without
impeding, help without hindering and constrain without binding, and let
you create applications that are easy to change and fun to work their
whole life long.

Transcript

1. @sandimetz Sep 2013
   Sandi Metz
   Rules
   1
   Sunday, September 15, 13
   

   View Slide

2. @sandimetz Sep 2013
   taboos
   2
   Sunday, September 15, 13
   

   View Slide

3. @sandimetz Sep 2013
   3
   Sunday, September 15, 13
   

   View Slide

4. @sandimetz Sep 2013
   laws
   4
   Sunday, September 15, 13
   

   View Slide

5. @sandimetz Sep 2013
   5
   Sunday, September 15, 13
   

   View Slide

6. @sandimetz Sep 2013
   norms
   6
   Sunday, September 15, 13
   

   View Slide

7. @sandimetz Sep 2013
   7
   Sunday, September 15, 13
   

   View Slide

8. @sandimetz Sep 2013
   obedience?
   8
   Sunday, September 15, 13
   

   View Slide

9. @sandimetz Sep 2013
   1
   self interest
   9
   Sunday, September 15, 13
   

   View Slide

10. @sandimetz Sep 2013
    10
    Sunday, September 15, 13
    

    View Slide

11. @sandimetz Sep 2013
    2
    identity
    status
    11
    Sunday, September 15, 13
    

    View Slide

12. @sandimetz Sep 2013
    12
    Sunday, September 15, 13
    

    View Slide

13. @sandimetz Sep 2013
    13
    Sunday, September 15, 13
    

    View Slide

14. @sandimetz Sep 2013
    14
    Sunday, September 15, 13
    

    View Slide

15. @sandimetz Sep 2013
    15
    Sunday, September 15, 13
    

    View Slide

16. @sandimetz Sep 2013
    16
    Sunday, September 15, 13
    

    View Slide

17. @sandimetz Sep 2013
    3
    authority
    17
    Sunday, September 15, 13
    

    View Slide

18. @sandimetz Sep 2013
    18
    Sunday, September 15, 13
    

    View Slide

19. @sandimetz Sep 2013
    19
    Sunday, September 15, 13
    

    View Slide

20. @sandimetz Sep 2013
    20
    Sunday, September 15, 13
    

    View Slide

21. @sandimetz Sep 2013
    4
    order
    21
    Sunday, September 15, 13
    

    View Slide

22. @sandimetz Sep 2013
    22
    Sunday, September 15, 13
    

    View Slide

23. @sandimetz Sep 2013
    23
    Sunday, September 15, 13
    

    View Slide

24. @sandimetz Sep 2013
    24
    Sunday, September 15, 13
    

    View Slide

25. @sandimetz Sep 2013
    5
    social
    sanctions
    25
    Sunday, September 15, 13
    

    View Slide

26. @sandimetz Sep 2013
    26
    Sunday, September 15, 13
    

    View Slide

27. @sandimetz Sep 2013
    6
    inherent
    sanctions
    27
    Sunday, September 15, 13
    

    View Slide

28. @sandimetz Sep 2013
    28
    Sunday, September 15, 13
    

    View Slide

29. @sandimetz Sep 2013
    7
    ignorance
    29
    Sunday, September 15, 13
    

    View Slide

30. @sandimetz Sep 2013
    30
    Sunday, September 15, 13
    

    View Slide

31. @sandimetz Sep 2013
    8
    habit
    31
    Sunday, September 15, 13
    

    View Slide

32. @sandimetz Sep 2013
    32
    Sunday, September 15, 13
    

    View Slide

33. @sandimetz Sep 2013
    33
    Sunday, September 15, 13
    

    View Slide

34. @sandimetz Sep 2013
    34
    Sunday, September 15, 13
    

    View Slide

35. @sandimetz Sep 2013
    taboos
    laws
    norms
    35
    Sunday, September 15, 13
    

    View Slide

36. @sandimetz Sep 2013
    self interest
    identity/status
    authority
    order
    social sanctions
    inherent sanctions
    ignorance
    habit
    36
    Sunday, September 15, 13
    

    View Slide

37. @sandimetz Sep 2013
    5
    Rules
    37
    Sunday, September 15, 13
    

    View Slide

38. @sandimetz Sep 2013
    5
    Constraints
    38
    Sunday, September 15, 13
    

    View Slide

39. @sandimetz Sep 2013
    100 lines
    per class
    39
    Sunday, September 15, 13
    

    View Slide

40. @sandimetz Sep 2013
    5 lines
    per method
    40
    Sunday, September 15, 13
    

    View Slide

41. @sandimetz Sep 2013
    4 parameters
    per method
    41
    Sunday, September 15, 13
    

    View Slide

42. @sandimetz Sep 2013
    1 instance var
    per rails view
    42
    Sunday, September 15, 13
    

    View Slide

43. @sandimetz Sep 2013
    2 class names
    per rails controller action
    43
    Sunday, September 15, 13
    

    View Slide

44. @sandimetz Sep 2013
    2 class names
    per rails controller action
    (business, presenter)
    43
    Sunday, September 15, 13
    

    View Slide

45. @sandimetz Sep 2013
    44
    Sunday, September 15, 13
    

    View Slide

46. @sandimetz Sep 2013
    Dispensation?
    44
    Sunday, September 15, 13
    

    View Slide

47. @sandimetz Sep 2013
    Dispensation?
    Convince
    your pair!*
    sdf
    *Rule #6
    44
    Sunday, September 15, 13
    

    View Slide

48. @sandimetz Sep 2013
    100 lines per class
       5 lines per method
       4 params per method
       1 ivar per view
       2 class names
    per controller action
    No
    More
    Than
    45
    Sunday, September 15, 13
    

    View Slide

49. @sandimetz Sep 2013
    consequences
    46
    Sunday, September 15, 13
    

    View Slide

50. @sandimetz Sep 2013
    bias towards
    small objects
    47
    Sunday, September 15, 13
    

    View Slide

51. @sandimetz Sep 2013
    bias towards
    POROs
    48
    Sunday, September 15, 13
    

    View Slide

52. @sandimetz Sep 2013
    bias away from
    dependencies
    49
    Sunday, September 15, 13
    

    View Slide

53. @sandimetz Sep 2013
    rule qualities
    50
    Sunday, September 15, 13
    

    View Slide

54. @sandimetz Sep 2013
    arbitrary
    cut-offs
    51
    Sunday, September 15, 13
    

    View Slide

55. @sandimetz Sep 2013
    consistent
    goals
    52
    Sunday, September 15, 13
    

    View Slide

56. @sandimetz Sep 2013
    tension
    53
    Sunday, September 15, 13
    

    View Slide

57. @sandimetz Sep 2013
    objects
    54
    Sunday, September 15, 13
    

    View Slide

58. @sandimetz Sep 2013
    objects
    vs
    55
    Sunday, September 15, 13
    

    View Slide

59. @sandimetz Sep 2013
    objects
    vs
    procedures
    56
    Sunday, September 15, 13
    

    View Slide

60. @sandimetz Sep 2013
    objects
    vs
    procedures
    57
    Sunday, September 15, 13
    

    View Slide

61. @sandimetz Sep 2013
    objects
    vs
    procedures
    58
    Sunday, September 15, 13
    

    View Slide

62. @sandimetz Sep 2013
    perspective
    59
    Sunday, September 15, 13
    

    View Slide

63. @sandimetz Sep 2013
    Rails app
    60
    Sunday, September 15, 13
    

    View Slide

64. @sandimetz Sep 2013
    Rails app
    vs
    61
    Sunday, September 15, 13
    

    View Slide

65. @sandimetz Sep 2013
    Rails app
    vs
    application
    that
    uses
    Rails
    62
    Sunday, September 15, 13
    

    View Slide

66. @sandimetz Sep 2013
    why follow
    rules?
    63
    Sunday, September 15, 13
    

    View Slide

67. @sandimetz Sep 2013
    self interest
    64
    Sunday, September 15, 13
    

    View Slide

68. @sandimetz Sep 2013
    signal others?
    65
    Sunday, September 15, 13
    

    View Slide

69. @sandimetz Sep 2013
    research
    66
    Sunday, September 15, 13
    

    View Slide

70. @sandimetz Sep 2013
    Erik O. Kimbrough
    Alexander Vostroknutov
    67
    Sunday, September 15, 13
    

    View Slide

71. @sandimetz Sep 2013
    Using Rules to
    Screen for Cooperative Types:
    Rule-Following and Restraint in
    Common Pool Resource Systems
    68
    Sunday, September 15, 13
    

    View Slide

72. @sandimetz Sep 2013
    Using Rules to
    Screen for Cooperative Types:
    Rule-Following and Restraint in
    Common Pool Resource Systems
    69
    Sunday, September 15, 13
    

    View Slide

73. @sandimetz Sep 2013
    study
    70
    Sunday, September 15, 13
    

    View Slide

74. @sandimetz Sep 2013
    study
    part 1
    71
    Sunday, September 15, 13
    

    View Slide

75. @sandimetz Sep 2013
    identify
    followers
    vs
    breakers
    72
    Sunday, September 15, 13
    

    View Slide

76. @sandimetz Sep 2013
    73
    Sunday, September 15, 13
    

    View Slide

77. @sandimetz Sep 2013
    Task: Walk--------->
    73
    Sunday, September 15, 13
    

    View Slide

78. @sandimetz Sep 2013
    Task: Walk--------->
    73
    Sunday, September 15, 13
    

    View Slide

79. @sandimetz Sep 2013
    Task: Walk--------->
    73
    Sunday, September 15, 13
    

    View Slide

80. @sandimetz Sep 2013
    given 8€
    74
    Sunday, September 15, 13
    

    View Slide

81. @sandimetz Sep 2013
    lose .08€ per second
    75
    Sunday, September 15, 13
    

    View Slide

82. @sandimetz Sep 2013
    red light = 5 seconds
    76
    Sunday, September 15, 13
    

    View Slide

83. @sandimetz Sep 2013
    “Wait for green light.”
    77
    Sunday, September 15, 13
    

    View Slide

84. @sandimetz Sep 2013
    some folks
    78
    Sunday, September 15, 13
    

    View Slide

85. @sandimetz Sep 2013
    79
    Sunday, September 15, 13
    

    View Slide

86. @sandimetz Sep 2013
    79
    Sunday, September 15, 13
    

    View Slide

87. @sandimetz Sep 2013
    80
    Sunday, September 15, 13
    

    View Slide

88. @sandimetz Sep 2013
    80
    Sunday, September 15, 13
    

    View Slide

89. @sandimetz Sep 2013
    81
    Sunday, September 15, 13
    

    View Slide

90. @sandimetz Sep 2013
    82
    Sunday, September 15, 13
    

    View Slide

91. @sandimetz Sep 2013
    82
    Sunday, September 15, 13
    

    View Slide

92. @sandimetz Sep 2013
    83
    Sunday, September 15, 13
    

    View Slide

93. @sandimetz Sep 2013
    etc...
    83
    Sunday, September 15, 13
    

    View Slide

94. @sandimetz Sep 2013
    other folks
    84
    Sunday, September 15, 13
    

    View Slide

95. @sandimetz Sep 2013
    85
    Sunday, September 15, 13
    

    View Slide

96. @sandimetz Sep 2013
    85
    Sunday, September 15, 13
    

    View Slide

97. @sandimetz Sep 2013
    study
    part 2
    86
    Sunday, September 15, 13
    

    View Slide

98. @sandimetz Sep 2013
    separate
    into like
    groups
    87
    Sunday, September 15, 13
    

    View Slide

99. @sandimetz Sep 2013
    play
    cooperative
    game
    88
    Sunday, September 15, 13
    

    View Slide

100. @sandimetz Sep 2013
     89
     Sunday, September 15, 13
     

     View Slide

101. @sandimetz Sep 2013
      4 players
     89
     Sunday, September 15, 13
     

     View Slide

102. @sandimetz Sep 2013
      4 players
     10 rounds
     89
     Sunday, September 15, 13
     

     View Slide

103. @sandimetz Sep 2013
      4 players
     10 rounds
     draw tokens
     89
     Sunday, September 15, 13
     

     View Slide

104. @sandimetz Sep 2013
     90
     Sunday, September 15, 13
     

     View Slide

105. @sandimetz Sep 2013
     90
     Sunday, September 15, 13
     

     View Slide

106. @sandimetz Sep 2013
     ∞
     90
     Sunday, September 15, 13
     

     View Slide

107. @sandimetz Sep 2013
     1
     1
     1
     1
     ∞
     90
     Sunday, September 15, 13
     

     View Slide

108. @sandimetz Sep 2013
     1
     1
     1
     1
     ∞
     90
     Sunday, September 15, 13
     

     View Slide

109. @sandimetz Sep 2013
     1
     1
     1
     1
     360
     ∞
     90
     Sunday, September 15, 13
     

     View Slide

110. @sandimetz Sep 2013
     1
     1
     1
     1
     360
     2
     ∞
     90
     Sunday, September 15, 13
     

     View Slide

111. @sandimetz Sep 2013
     each player draws
     60 tokens
     per round
     91
     Sunday, September 15, 13
     

     View Slide

112. @sandimetz Sep 2013
     Round 1
     92
     Sunday, September 15, 13
     

     View Slide

113. @sandimetz Sep 2013
     Round 1
     120
     92
     Sunday, September 15, 13
     

     View Slide

114. @sandimetz Sep 2013
     120
     Regeneration
     93
     Sunday, September 15, 13
     

     View Slide

115. @sandimetz Sep 2013
     120 * .5
     Regeneration
     94
     Sunday, September 15, 13
     

     View Slide

116. @sandimetz Sep 2013
     180
     Regeneration
     95
     Sunday, September 15, 13
     

     View Slide

117. @sandimetz Sep 2013
     Regeneration
     96
     Sunday, September 15, 13
     

     View Slide

118. @sandimetz Sep 2013
     Regeneration
     96
     Sunday, September 15, 13
     

     View Slide

119. @sandimetz Sep 2013
     30
     Regeneration
     97
     Sunday, September 15, 13
     

     View Slide

120. @sandimetz Sep 2013
     30
     Regeneration
     97
     Sunday, September 15, 13
     

     View Slide

121. @sandimetz Sep 2013
     Round 2
     180 remain??
     98
     Sunday, September 15, 13
     

     View Slide

122. @sandimetz Sep 2013
     Round 2
     180 - 30 = 150
     99
     Sunday, September 15, 13
     

     View Slide

123. @sandimetz Sep 2013
     Round 2
     180 - 30 = 150
     150 / 4 = 37.5
     100
     Sunday, September 15, 13
     

     View Slide

124. @sandimetz Sep 2013
     Round 2
     37!
     101
     Sunday, September 15, 13
     

     View Slide

125. @sandimetz Sep 2013
     180
     Round 2
     1
     1
     1
     1
     2
     102
     Sunday, September 15, 13
     

     View Slide

126. @sandimetz Sep 2013
     Round 2
     103
     Sunday, September 15, 13
     

     View Slide

127. @sandimetz Sep 2013
     Round 2
     32
     103
     Sunday, September 15, 13
     

     View Slide

128. @sandimetz Sep 2013
     32
     Regeneration
     104
     Sunday, September 15, 13
     

     View Slide

129. @sandimetz Sep 2013
     32 * .5
     Regeneration
     105
     Sunday, September 15, 13
     

     View Slide

130. @sandimetz Sep 2013
     48
     Regeneration
     106
     Sunday, September 15, 13
     

     View Slide

131. @sandimetz Sep 2013
     48
     Regeneration
     Etc...
     106
     Sunday, September 15, 13
     

     View Slide

132. @sandimetz Sep 2013
     (current - 30) / 4
     107
     Sunday, September 15, 13
     

     View Slide

133. @sandimetz Sep 2013
     results
     108
     Sunday, September 15, 13
     

     View Slide

134. @sandimetz Sep 2013
     followers
     109
     Sunday, September 15, 13
     

     View Slide

135. @sandimetz Sep 2013
     followers
     cooperate for mutual
     long term gain
     109
     Sunday, September 15, 13
     

     View Slide

136. @sandimetz Sep 2013
     breakers
     110
     Sunday, September 15, 13
     

     View Slide

137. @sandimetz Sep 2013
     breakers
     throw team under bus
     110
     Sunday, September 15, 13
     

     View Slide

138. @sandimetz Sep 2013
     60!
     60!
     60!
     60!
     111
     Sunday, September 15, 13
     

     View Slide

139. @sandimetz Sep 2013
     mixed groups
     112
     Sunday, September 15, 13
     

     View Slide

140. @sandimetz Sep 2013
     mixed groups
     behave like
     breaker groups
     112
     Sunday, September 15, 13
     

     View Slide

141. @sandimetz Sep 2013
     30!
     30!
     30!
     50!
     113
     Sunday, September 15, 13
     

     View Slide

142. @sandimetz Sep 2013
     50!
     114
     Sunday, September 15, 13
     

     View Slide

143. @sandimetz Sep 2013
     60!
     60!
     60!
     50!
     114
     Sunday, September 15, 13
     

     View Slide

144. @sandimetz Sep 2013
     consequences
     (reprise)
     115
     Sunday, September 15, 13
     

     View Slide

145. @sandimetz Sep 2013
     bias towards
     small objects
     116
     Sunday, September 15, 13
     

     View Slide

146. @sandimetz Sep 2013
     bias towards
     POROs
     117
     Sunday, September 15, 13
     

     View Slide

147. @sandimetz Sep 2013
     bias away from
     dependencies
     118
     Sunday, September 15, 13
     

     View Slide

148. @sandimetz Sep 2013
     bias towards
     collaboration
     119
     Sunday, September 15, 13
     

     View Slide

149. @sandimetz Sep 2013
     bias towards
     collaboration
     119
     Sunday, September 15, 13
     

     View Slide

150. @sandimetz Sep 2013
     self interest
     identity/status
     authority
     order
     social sanctions
     inherent sanctions
     ignorance
     habit
     120
     Sunday, September 15, 13
     

     View Slide

151. @sandimetz Sep 2013
     9
     signal cooperation
     121
     Sunday, September 15, 13
     

     View Slide

152. @sandimetz Sep 2013
     rules matter
     122
     Sunday, September 15, 13
     

     View Slide

153. @sandimetz Sep 2013
     write
     better
     software
     123
     Sunday, September 15, 13
     

     View Slide

154. @sandimetz Sep 2013
     find
     trustworthy
     humans
     124
     Sunday, September 15, 13
     

     View Slide

155. @sandimetz Sep 2013
     Thanks
     125
     Sunday, September 15, 13
     

     View Slide

156. @sandimetz Sep 2013
     Credits
     http://www.flickr.com/photos/paul-w-locke/1792803096/ Cannibal Pumpkins
     http://www.flickr.com/photos/john_pp/3155064087/ 100K Speed limit sign on cliff with hiker
     http://www.flickr.com/photos/paphio/272769602/ Cops cheek kissing
     http://www.flickr.com/photos/pixel8-rcrd/5791227393/ kid winning contest
     http://www.flickr.com/photos/fluffy_steve/2537798898/ two goths
     http://www.flickr.com/photos/bobjagendorf/3064198102/ wall street shuffle
     http://www.flickr.com/photos/pdsphil/278060802/ rubyconf room 2006
     http://www.flickr.com/photos/danicuki/6319528505/ konstanin and jose
     http://www.flickr.com/photos/lucasrenan/5142409437/ 3 ruby nerds, 10/26/2010
     http://www.flickr.com/photos/85529750@N00/5200928365/ pope barcelona
     http://www.flickr.com/photos/nathaninsandiego/3783772122/ umpire
     http://www.flickr.com/photos/rrrodrigo/4664885112/ matz
     http://www.flickr.com/photos/85529750@N00/5200928365/ pope barcelona
     http://www.flickr.com/photos/nathaninsandiego/3783772122/ umpire
     http://www.flickr.com/photos/rrrodrigo/4664885112/ matz
     http://www.flickr.com/photos/z_wenjie/7820625836 pansies
     http://www.flickr.com/photos/haikugirl/4813516858/ trees
     http://www.flickr.com/photos/emsef/2407145479/ bus stop queue
     http://www.flickr.com/photos/theretrographer/9228096325/ rows of jail cells brightly lit
     126
     Sunday, September 15, 13
     

     View Slide

157. @sandimetz Sep 2013
     Credits
     http://www.flickr.com/photos/jakebouma/102485568/ Car cliff warning
     http://www.flickr.com/photos/burge009/5215723703/ free tatoos
     http://www.flickr.com/photos/singularitysummit/6261754179/ one swarming robot
     http://www.flickr.com/photos/singularitysummit/6262287656/ swarming robots swarming
     http://www.flickr.com/photos/osakasteve/17178084/ swarming robots in a line
     http://en.wikipedia.org/wiki/Social_rule_system_theory
     Kinbrough, Erik O., Vosroknutov, Alexander (2012 draft), Using Rules to Screen for Cooperative
     Types: Rule-Following and Restraint in Common Pool Resource Systems
     127
     Sunday, September 15, 13
     

     View Slide

158. http://poodr.com
     Sandi Metz
     @sandimetz
     @sandimetz Sep 2013
     128
     Sunday, September 15, 13
     

     View Slide

159. @sandimetz Sep 2013
     Questions?
     129
     Sunday, September 15, 13
     

     View Slide

160. http://poodr.com
     Sandi Metz
     @sandimetz
     @sandimetz Sep 2013
     130
     Sunday, September 15, 13
     

     View Slide