SlideShare a Scribd company logo

hafentalks #7 - Sandi Metz: Go Ahead, Make a Mess

hafentalks, profile picture
hafentalks

The document discusses the complexities of object-oriented design, emphasizing the importance of recognizing and managing 'messiness' in code. It highlights how knowledge and stability are intertwined with dependencies and potential pitfalls, urging developers to navigate these challenges effectively. Through various examples, the document illustrates the impact of dependency management and optimization strategies in coding practices.

Software
Related topics:
Insights on Software Development
1 of 268
Download to read offline
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
@sandimetz Jul 2017 Go Ahead Make a Mess Sandi Metz
@sandimetz Jul 2017 Project Life Cycle
@sandimetz Jul 2017 Satisfaction Timeline Start Beta 1.0 2.0 Today
@sandimetz Jul 2017 Satisfaction Timeline Start Beta 1.0 2.0 Today
@sandimetz Jul 2017 Satisfaction
@sandimetz Jul 2017 Satisfaction Those who cannot remember the past are condemned to repeat it.
@sandimetz Jul 2017
@sandimetz Jul 2017 Satisfaction
@sandimetz Jul 2017 The Mess
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Knowledge
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Dependencies
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Stability
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Hope
@sandimetz Jul 2017
@sandimetz Jul 2017 Satisfaction Timeline Start Beta 1.0 2.0 Today
@sandimetz Jul 2017 Timeline Start Beta 1.0 2.0 Today Object-Oriented Design
@sandimetz Jul 2017 Timeline Start Beta 1.0 2.0 Today Stop worrying and learn to love the mess Object-Oriented Design
@sandimetz Jul 2017
@sandimetz Jul 2017 Label the Knowledge
@sandimetz Jul 2017 Label the Knowledge Complicate the Code
@sandimetz Jul 2017 Label the Knowledge Complicate the Code Isolate the Instability
@sandimetz Jul 2017 Label the Knowledge Complicate the Code Isolate the Instability Manage the Mess
@sandimetz Jul 2017 Example #1 Label the Knowledge
@sandimetz Jul 2017 Example #1 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end
@sandimetz Jul 2017 Example #1 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end
@sandimetz Jul 2017 Example #1 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end
@sandimetz Jul 2017 Example #1 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end
@sandimetz Jul 2017 Example #1 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end
@sandimetz Jul 2017 Example #1 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end MESS
@sandimetz Jul 2017 Example #1 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end Omega Mess
@sandimetz Jul 2017
@sandimetz Jul 2017 Omega Mess
@sandimetz Jul 2017 Omega Mess End of the Line
@sandimetz Jul 2017 Omega Mess End of the Line No Dependencies
@sandimetz Jul 2017 Omega Mess End of the Line No Dependencies No Dependents
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Knowledge Stability
@sandimetz Jul 2017 External Knowledge Stability
@sandimetz Jul 2017 Internal External Knowledge Stability
@sandimetz Jul 2017 Internal External Knowledge Stability Low High
@sandimetz Jul 2017 Internal External Knowledge Stability Low High
@sandimetz Jul 2017 Internal External Knowledge Stability Low High
@sandimetz Jul 2017 Internal External Knowledge Stability Low High
@sandimetz Jul 2017 Internal External Knowledge Stability Low High
@sandimetz Jul 2017 Internal External Knowledge Stability Low High
@sandimetz Jul 2017 Internal External Knowledge Stability Low High
@sandimetz Jul 2017 Dependencies Shock
@sandimetz Jul 2017 Dependencies Shock Game
@sandimetz Jul 2017
@sandimetz Jul 2017 Omega
@sandimetz Jul 2017 Omega
@sandimetz Jul 2017
@sandimetz Jul 2017 Omega Mess
@sandimetz Jul 2017 Omega Mess Hides behind the message
@sandimetz Jul 2017 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end end Example #1
@sandimetz Jul 2017 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end end It’s not about the code Example #1
@sandimetz Jul 2017 It’s about the message
@sandimetz Jul 2017
@sandimetz Jul 2017 Interlude
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Public API
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Public API Expose
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Public API Private Behavior Expose
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Public API Private Behavior Expose Hide
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Public API Private Behavior Dependencies Expose Hide
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Public API Private Behavior Dependencies Expose Hide Minimize
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Public API Private Behavior Dependencies Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot 1 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method (expose) 2. cost calculation Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method (expose) 2. cost calculation Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method (expose) 2. cost calculation Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Plot 1 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot 1 2 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method (expose) 2. cost calculation (hide) Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method (expose) 2. cost calculation (hide) Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method (expose) 2. cost calculation (hide) Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method (expose) 2. cost calculation (hide) Game depends on 3. cost message 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot 3 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation Game depends on 3. cost message (minimize) 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation Game depends on 3. cost message (minimize) 4. Shock class name 5. cost receiver
@sandimetz Jul 2017 Knowledge Plot 3 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot 4 53 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot 4 53 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot ? 4 53 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation Game depends on 3. cost message (minimize) 4. Shock class name 5. cost receiver ???
@sandimetz Jul 2017 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end end Example #1
@sandimetz Jul 2017 What is the future cost of doing nothing now?
@sandimetz Jul 2017 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end end Example #1
@sandimetz Jul 2017 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end end I would inject this dependency Example #1
@sandimetz Jul 2017 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end end I would inject this dependency I would neaten this mess Example #1
@sandimetz Jul 2017 class Game def shock_cost Shock.new.cost end end class Shock def cost # lines of messy math # ... # which eventually return cost end end I would inject this dependency I would neaten this mess You might not Example #1
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Example #2 Complicate the code
@sandimetz Jul 2017 Example #2 Complicate the code Shocks vary in cost
@sandimetz Jul 2017 Example #2 class Game def shock_cost(type) Shock.new(type).cost end end
@sandimetz Jul 2017 Example #2 class Game def shock_cost(type) Shock.new(type).cost end end
@sandimetz Jul 2017 Example #2 class Game def shock_cost(type) Shock.new(type).cost end end
@sandimetz Jul 2017 Example #2 class Shock attr_reader :type def initialize(type) # ... def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017 Example #2 class Shock attr_reader :type def initialize(type) # ... def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017 Example #2 class Shock attr_reader :type def initialize(type) # ... def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017 Example #2 class Shock attr_reader :type def initialize(type) # ... def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017 Example #2 class Shock attr_reader :type def initialize(type) # ... def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Omega?
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation 3. 4.
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. cost calculation 3. 4.
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation Omega Mess?
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation Omega Mess?
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation Meta Knowledge
@sandimetz Jul 2017
@sandimetz Jul 2017 Meta Knowledge
@sandimetz Jul 2017 Meta Knowledge Knowledge about Knowledge
@sandimetz Jul 2017
@sandimetz Jul 2017 Meta Knowledge
@sandimetz Jul 2017 Meta Knowledge The Domain of Design
@sandimetz Jul 2017
@sandimetz Jul 2017 Interlude
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Plot 2 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot 2 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations (move) 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations (move) 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot 3 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations (move) 3. four shock types (move) 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations (move) 3. four shock types (move) 4. which type gets what calculation
@sandimetz Jul 2017 Knowledge Plot Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Plot 4 Stable Unstable Within My Purpose Outside of My Purpose Expose Hide Minimize Move
@sandimetz Jul 2017 Knowledge Shock knows 1. cost method 2. four shock cost calculations (move) 3. four shock types (move) 4. which type gets what calculation (min)
@sandimetz Jul 2017 Preference
@sandimetz Jul 2017 Preference Send a message
@sandimetz Jul 2017 Preference Send a message rather than implement behavior
@sandimetz Jul 2017 Move it
@sandimetz Jul 2017 Move it Find the message
@sandimetz Jul 2017 Move it Find the message (Create the object)
@sandimetz Jul 2017 Move it Find the message (Create the object) Send the message
@sandimetz Jul 2017
@sandimetz Jul 2017 Example #3 Composition
@sandimetz Jul 2017 #3 Composition def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017 #3 Composition def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017 #3 Composition def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017 #3 Composition def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end What’s the message?
@sandimetz Jul 2017 #3 Composition def cost case type when :front someObligingObj.compute when :rear # a slightly different mess when :lefty # another variant else # and so on. end end
@sandimetz Jul 2017 #3 Composition def cost case type when :front someObligingObj.compute when :rear # a slightly different mess when :lefty # another variant else # and so on. end end ???
@sandimetz Jul 2017 def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition class FrontShockCost def compute # the original mess end end
@sandimetz Jul 2017 def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition class FrontShockCost def compute # the original mess end end
@sandimetz Jul 2017 def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition class FrontShockCost def compute # the original mess end end Hide the Mess
@sandimetz Jul 2017 def cost case type when :front FrontShockCost.new.compute when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition class FrontShockCost def compute # the original mess end end
@sandimetz Jul 2017 def cost case type when :front FrontShockCost.new.compute when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition class FrontShockCost def compute # the original mess end end Send the Message
@sandimetz Jul 2017 def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition
@sandimetz Jul 2017 def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition
@sandimetz Jul 2017 def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition
@sandimetz Jul 2017 def cost case type when :front # the original mess when :rear # a slightly different mess when :lefty # another variant else # and so on. end end #3 Composition Hide all of the Messes
@sandimetz Jul 2017 #3 Composition class FrontShockCost def compute # the original mess end end class RearShockCost def compute # slightly changed mess end end # etc
@sandimetz Jul 2017 #3 Composition class FrontShockCost def compute # the original mess end end class RearShockCost def compute # slightly changed mess end end # etc
@sandimetz Jul 2017 #3 Composition class FrontShockCost def compute # the original mess end end class RearShockCost def compute # slightly changed mess end end # etc
@sandimetz Jul 2017 #3 Composition class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end
@sandimetz Jul 2017 #3 Composition class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end Send the Message
@sandimetz Jul 2017 #3 Composition class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end
@sandimetz Jul 2017 #3 Composition class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end Really?
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four shock cost calculations 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four ShockCostxx classes 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four ShockCostxx classes 3. four shock types 4. which type gets what calculation
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four ShockCostxx classes 3. four shock types 4. which type gets what class
@sandimetz Jul 2017 Good News Calculations are isolated
@sandimetz Jul 2017 Bad News Still have dependencies
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end #3 Composition
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end #3 Composition
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end when :front #3 Composition
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end when :foo FooShockCost.new.compute #3 Composition
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end when :foo FooShockCost.new.compute #3 Composition
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end when :foo FooShockCost.new.compute #3 Composition Conventionoverconfiguration
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end when :foo FooShockCost.new.compute class_name = type.to_s.capitalize + "ShockCost" #3 Composition Conventionoverconfiguration
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end class_name = type.to_s.capitalize + "ShockCost" eval(class_name).new.compute #3 Composition Conventionoverconfiguration when :foo FooShockCost.new.compute
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end class_name = type.to_s.capitalize + "ShockCost" eval(class_name).new.compute Object.const_get(class_name).new.compute #3 Composition Conventionoverconfiguration when :foo FooShockCost.new.compute
@sandimetz Jul 2017 class Shock def cost(type) case type when :front FrontShockCost.new.compute when :rear RearShockCost.new.compute when :lefty LeftyShockCost.new.compute else ShockCost.new.compute end end # ... end class_name = type.to_s.capitalize + "ShockCost" eval(class_name).new.compute Object.const_get(class_name).new.compute class_name.constantize.new.compute #3 Composition Conventionoverconfiguration when :foo FooShockCost.new.compute
@sandimetz Jul 2017 Example #3 class Shock def cost(type) class_name = (type.to_s.capitalize + "ShockCost") Object.const_get(class_name).new.compute end end
@sandimetz Jul 2017 Example #3 class Shock def cost(type) class_name = (type.to_s.capitalize + "ShockCost") Object.const_get(class_name).new.compute end end
@sandimetz Jul 2017 Example #3 class Shock def cost(type) class_name = (type.to_s.capitalize + "ShockCost") Object.const_get(class_name).new.compute end end Factory
@sandimetz Jul 2017 We <3 Factories
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four ShockCostxx classes 3. four shock types 4. which type gets what class
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four ShockCostxx classes 3. four shock types 4. which type gets what class
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four ShockCostxx classes 3. four shock types 4. which type gets what class
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. four ShockCostxx classes 3. four shock types 4. which type gets what class
@sandimetz Jul 2017 Meta Knowledge Shock knows 1. cost method 2. the convention
Before @sandimetz Jul 2017 #3 Composition def cost case type when :front # the original mess when :rear # a slightly # different mess when :lefty # another variant else # and so on. end end
Before @sandimetz Jul 2017 #3 Composition def cost case type when :front # the original mess when :rear # a slightly # different mess when :lefty # another variant else # and so on. end end Many changes affect this code
After @sandimetz Jul 2017 Example #3 class Shock def cost(type) class_name = (type.to_s.capitalize + "ShockCost") Object.const_get(class_name).new.compute end end
After @sandimetz Jul 2017 Example #3 class Shock def cost(type) class_name = (type.to_s.capitalize + "ShockCost") Object.const_get(class_name).new.compute end end
After @sandimetz Jul 2017 Example #3 class Shock def cost(type) class_name = (type.to_s.capitalize + "ShockCost") Object.const_get(class_name).new.compute end def coster(type) Object.const_get(type.to_s.capitalize + “ShockCost").new end end
After @sandimetz Jul 2017 Example #3 class Shock def cost(type) coster(type).compute end def coster(type) Object.const_get(type.to_s.capitalize + “ShockCost").new end end
After @sandimetz Jul 2017 Example #3 class Shock def cost(type) coster(type).compute end def coster(type) Object.const_get(type.to_s.capitalize + “ShockCost").new end end Few changes affect this code
After @sandimetz Jul 2017 Example #3 class FrontShockCost def compute # the original mess end end class Shock def cost(type) coster(type).compute end def coster(type) Object.const_get(type.to_s.capitalize + “ShockCost").new end end Few changes affect this code
After @sandimetz Jul 2017 Example #3 class FrontShockCost def compute # the original mess end end class Shock def cost(type) coster(type).compute end def coster(type) Object.const_get(type.to_s.capitalize + “ShockCost").new end end class RearShockCost def compute # slightly changed mess end end Few changes affect this code
After @sandimetz Jul 2017 Example #3 class FrontShockCost def compute # the original mess end end class Shock def cost(type) coster(type).compute end def coster(type) Object.const_get(type.to_s.capitalize + “ShockCost").new end end class RearShockCost def compute # slightly changed mess end end Etc... Few changes affect this code
After @sandimetz Jul 2017 Example #3 class FrontShockCost def compute # the original mess end end class Shock def cost(type) coster(type).compute end def coster(type) Object.const_get(type.to_s.capitalize + “ShockCost").new end end class RearShockCost def compute # slightly changed mess end end Etc... Few changes affect this code Need a new one? Follow the convention!
@sandimetz Jul 2017 Composition
@sandimetz Jul 2017 Shock ?
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 Shock
@sandimetz Jul 2017 The Role
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Reprise Find the message (Create the object) Send the message
@sandimetz Jul 2017 Omega Mess
@sandimetz Jul 2017 Omega Mess Hide It
@sandimetz Jul 2017 Meta Knowledge
@sandimetz Jul 2017 Meta Knowledge Organize It
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Depend on Stability
@sandimetz Jul 2017 Depend on Stability Find the Message
@sandimetz Jul 2017 Isolate Uncertainty
@sandimetz Jul 2017 Isolate Uncertainty Hide the Mess
@sandimetz Jul 2017 We stand on the shoulders of giants
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017
@sandimetz Jul 2017 Thanks Sandi Metz
@sandimetz Jul 2017 http://www.flickr.com/photos/slumadridcampus/5736110401/ http://www.flickr.com/photos/jennifermarquez/4441957235/ http://www.flickr.com/photos/58789412@N00/4106497024/ http://www.flickr.com/photos/27927484@N00/264072199/ http://www.flickr.com/photos/alexindigo/2572565946/in/photostream/ http://www.flickr.com/photos/moje_moje/4500967490/ http://www.flickr.com/photos/dr_nixon/4366089630/ http://www.flickr.com/photos/question_everything/4778500858/ http://www.flickr.com/photos/thegforcers/6202236364/in/photostream/ http://www.flickr.com/photos/jeffhester/2785524078/ http://www.flickr.com/photos/thegforcers/6040964794/in/photostream/ http://www.flickr.com/photos/magnus_akselvoll/4741056713/ http://www.flickr.com/photos/chiotsrun/6553699405/ http://www.flickr.com/photos/45682148@N05/7943889710/ http://www.flickr.com/photos/piper/393928412/ http://www.flickr.com/photos/thegforcers/6202237588/in/photostream/ http://www.flickr.com/photos/juju2nantes/5895167252/ Credits
@sandimetz Jul 2017 http://www.flickr.com/photos/harlequeen/3323992902/ http://www.flickr.com/photos/thegforcers/6114852991/in/photostream/ http://www.flickr.com/photos/qatarperegrine/5040119481/ http://www.flickr.com/photos/reneeanddolan/6152499201/ http://www.flickr.com/photos/tchelseat/7628965564/ http://www.flickr.com/photos/clappstar/1064543301/ http://www.flickr.com/photos/nycarthur/2482218423/ http://www.flickr.com/photos/oliverlaumann/5525877007/ http://www.websequencediagrams.com/ Credits
@sandimetz http://poodr.com Jul 2017
@sandimetz http://99bottlesbook.com Jul 2017
@sandimetz Sandi Metz @sandimetz http://sandimetz.com Jul 2017

More Related Content

PDF
hafentalks #10 - Jurgen Appelo: "Managing for Happiness"
hafentalks
 
PDF
hafentalks #9 - Jeff Gothelf: "Almost Everything I've Learned from 6 Years of...
hafentalks
 
PDF
hafentalks #5 - André Häusling: "Mythos Agilität – über Sinn und Unsinn des a...
hafentalks
 
PDF
hafentalks #4 -Kontantin Haase: Wie wir Gehaltsverhandlungen durch eine Sinat...
hafentalks
 
PDF
hafentalks #1 - Chad Fowler: Impermanence as the key to good systems thinking
hafentalks
 
PDF
2024 Trend Updates: What Really Works In SEO & Content Marketing
Search Engine Journal
 
PDF
Storytelling For The Web: Integrate Storytelling in your Design Process
Chiara Aliotta
 
PDF
Artificial Intelligence, Data and Competition – SCHREPEL – June 2024 OECD dis...
OECD Directorate for Financial and Enterprise Affairs
 
hafentalks #10 - Jurgen Appelo: "Managing for Happiness"
hafentalks
 
hafentalks #9 - Jeff Gothelf: "Almost Everything I've Learned from 6 Years of...
hafentalks
 
hafentalks #5 - André Häusling: "Mythos Agilität – über Sinn und Unsinn des a...
hafentalks
 
hafentalks #4 -Kontantin Haase: Wie wir Gehaltsverhandlungen durch eine Sinat...
hafentalks
 
hafentalks #1 - Chad Fowler: Impermanence as the key to good systems thinking
hafentalks
 
2024 Trend Updates: What Really Works In SEO & Content Marketing
Search Engine Journal
 
Storytelling For The Web: Integrate Storytelling in your Design Process
Chiara Aliotta
 
Artificial Intelligence, Data and Competition – SCHREPEL – June 2024 OECD dis...
OECD Directorate for Financial and Enterprise Affairs
 

Recently uploaded (20)

PDF
Comprehensive Salesforce Implementation Services.pdf
VALiNTRY360
 
PDF
ShowUs: Pharo Stream Deck (ESUG 2025, Gdansk)
ESUG
 
DOCX
The Five Best AI Cover Tools in 2025.docx
aivoicelabofficial
 
PPTX
Presentation of Computer CLASS 2 .pptx
darshilchaudhary558
 
PPTX
Save Business Costs with CRM Software for Insurance Agents
Insurance Tech Services
 
PDF
How Creative Agencies Leverage Project Management Software.pdf
Orangescrum
 
PDF
Community & News Update Q2 Meet Up 2025
VictoriaMetrics
 
PDF
How to Confidently Manage Project Budgets
OnePlan Solutions
 
PDF
Microsoft Teams Essentials; The pricing and the versions_PDF.pdf
Q-Advise
 
PPTX
Safe Confined Space Entry Monitoring_ Singapore Experts.pptx
prasadexiga0
 
PDF
Jenkins: An open-source automation server powering CI/CD Automation
SaikatBasu37
 
PDF
Become an Agentblazer Champion Challenge Kickoff
Dele Amefo
 
PDF
How to Migrate SBCGlobal Email to Yahoo Easily
raymondjones7273
 
PPTX
Odoo Consulting Services by CandidRoot Solutions
CandidRoot Solutions Private Limited
 
PDF
IEEE-CS Tech Predictions, SWEBOK and Quantum Software: Towards Q-SWEBOK
Hironori Washizaki
 
PDF
The Future of Smart Factories Why Embedded Analytics Leads the Way
Varsha Nayak
 
PDF
Best Smart Port Software of 2025 Why Envision Leads the Market.pdf
Envision Enterprise Solutions
 
PDF
Build Multi-agent using Agent Development Kit
FadyIbrahim23
 
PDF
Micromaid: A simple Mermaid-like chart generator for Pharo
ESUG
 
PPTX
What to Capture When It Breaks: 16 Artifacts That Reveal Root Causes
Tier1 app
 
Comprehensive Salesforce Implementation Services.pdf
VALiNTRY360
 
ShowUs: Pharo Stream Deck (ESUG 2025, Gdansk)
ESUG
 
The Five Best AI Cover Tools in 2025.docx
aivoicelabofficial
 
Presentation of Computer CLASS 2 .pptx
darshilchaudhary558
 
Save Business Costs with CRM Software for Insurance Agents
Insurance Tech Services
 
How Creative Agencies Leverage Project Management Software.pdf
Orangescrum
 
Community & News Update Q2 Meet Up 2025
VictoriaMetrics
 
How to Confidently Manage Project Budgets
OnePlan Solutions
 
Microsoft Teams Essentials; The pricing and the versions_PDF.pdf
Q-Advise
 
Safe Confined Space Entry Monitoring_ Singapore Experts.pptx
prasadexiga0
 
Jenkins: An open-source automation server powering CI/CD Automation
SaikatBasu37
 
Become an Agentblazer Champion Challenge Kickoff
Dele Amefo
 
How to Migrate SBCGlobal Email to Yahoo Easily
raymondjones7273
 
Odoo Consulting Services by CandidRoot Solutions
CandidRoot Solutions Private Limited
 
IEEE-CS Tech Predictions, SWEBOK and Quantum Software: Towards Q-SWEBOK
Hironori Washizaki
 
The Future of Smart Factories Why Embedded Analytics Leads the Way
Varsha Nayak
 
Best Smart Port Software of 2025 Why Envision Leads the Market.pdf
Envision Enterprise Solutions
 
Build Multi-agent using Agent Development Kit
FadyIbrahim23
 
Micromaid: A simple Mermaid-like chart generator for Pharo
ESUG
 
What to Capture When It Breaks: 16 Artifacts That Reveal Root Causes
Tier1 app
 
Ad

Featured (20)

PDF
How to Leverage AI to Boost Employee Wellness - Lydia Di Francesco - SocialHR...
SocialHRCamp
 
PDF
2024 State of Marketing Report – by Hubspot
Marius Sescu
 
PDF
Everything You Need To Know About ChatGPT
Expeed Software
 
PDF
Product Design Trends in 2024 | Teenage Engineerings
Pixeldarts
 
PDF
How Race, Age and Gender Shape Attitudes Towards Mental Health
ThinkNow
 
PDF
AI Trends in Creative Operations 2024 by Artwork Flow.pdf
marketingartwork
 
PDF
Skeleton Culture Code
Skeleton Technologies
 
PDF
PEPSICO Presentation to CAGNY Conference Feb 2024
Neil Kimberley
 
PDF
Content Methodology: A Best Practices Report (Webinar)
contently
 
PPTX
How to Prepare For a Successful Job Search for 2024
Albert Qian
 
PDF
Social Media Marketing Trends 2024 // The Global Indie Insights
Kurio // The Social Media Age(ncy)
 
PDF
Trends In Paid Search: Navigating The Digital Landscape In 2024
Search Engine Journal
 
PDF
5 Public speaking tips from TED - Visualized summary
SpeakerHub
 
PDF
ChatGPT and the Future of Work - Clark Boyd
Clark Boyd
 
PDF
Getting into the tech field. what next
Tessa Mero
 
PDF
Google's Just Not That Into You: Understanding Core Updates & Search Intent
Lily Ray
 
PDF
How to have difficult conversations
Rajiv Jayarajah, MAppComm, ACC
 
PDF
Introduction to Data Science
Christy Abraham Joy
 
PDF
Time Management & Productivity - Best Practices
Vit Horky
 
PDF
The six step guide to practical project management
MindGenius
 
How to Leverage AI to Boost Employee Wellness - Lydia Di Francesco - SocialHR...
SocialHRCamp
 
2024 State of Marketing Report – by Hubspot
Marius Sescu
 
Everything You Need To Know About ChatGPT
Expeed Software
 
Product Design Trends in 2024 | Teenage Engineerings
Pixeldarts
 
How Race, Age and Gender Shape Attitudes Towards Mental Health
ThinkNow
 
AI Trends in Creative Operations 2024 by Artwork Flow.pdf
marketingartwork
 
Skeleton Culture Code
Skeleton Technologies
 
PEPSICO Presentation to CAGNY Conference Feb 2024
Neil Kimberley
 
Content Methodology: A Best Practices Report (Webinar)
contently
 
How to Prepare For a Successful Job Search for 2024
Albert Qian
 
Social Media Marketing Trends 2024 // The Global Indie Insights
Kurio // The Social Media Age(ncy)
 
Trends In Paid Search: Navigating The Digital Landscape In 2024
Search Engine Journal
 
5 Public speaking tips from TED - Visualized summary
SpeakerHub
 
ChatGPT and the Future of Work - Clark Boyd
Clark Boyd
 
Getting into the tech field. what next
Tessa Mero
 
Google's Just Not That Into You: Understanding Core Updates & Search Intent
Lily Ray
 
How to have difficult conversations
Rajiv Jayarajah, MAppComm, ACC
 
Introduction to Data Science
Christy Abraham Joy
 
Time Management & Productivity - Best Practices
Vit Horky
 
The six step guide to practical project management
MindGenius
 
Ad

hafentalks #7 - Sandi Metz: Go Ahead, Make a Mess