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@sandimetz Sept 2012
Go Ahead
Make a Mess
Sandi Metz
1
Friday, September 14, 2012
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@sandimetz Sept 2012
Life Cycle
of a
Rails Project
2
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@sandimetz Sept 2012
Start Beta 1.0 2.0 Today
Satisfaction
Timeline
3
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@sandimetz Sept 2012
Start Beta 1.0 2.0 Today
Satisfaction
Timeline
4
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@sandimetz Sept 2012
Satisfaction
5
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@sandimetz Sept 2012
Satisfaction
Those who cannot remember the past
are condemned to repeat it.
5
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@sandimetz Sept 2012
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@sandimetz Sept 2012
Satisfaction
7
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@sandimetz Sept 2012
The Mess
8
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@sandimetz Sept 2012
9
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10
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@sandimetz Sept 2012
Knowledge
11
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@sandimetz Sept 2012
Dependencies
14
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15
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@sandimetz Sept 2012
Stability
17
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@sandimetz Sept 2012
Hope
21
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@sandimetz Sept 2012
Start Beta 1.0 2.0 Today
Satisfaction
Timeline
23
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@sandimetz Sept 2012
Object-Oriented Design
Stop worrying
and
learn to love the mess
24
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25
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Label the Knowledge
26
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Label the Knowledge
Complicate the Code
27
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Label the Knowledge
Complicate the Code
Isolate the Instability
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Label the Knowledge
Complicate the Code
Isolate the Instability
Manage the Mess
29
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@sandimetz Sept 2012
Example #1
Label the Knowledge
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@sandimetz Sept 2012
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
31
Friday, September 14, 2012
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Slide 33 text
@sandimetz Sept 2012
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
31
Friday, September 14, 2012
Slide 34
Slide 34 text
@sandimetz Sept 2012
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
31
Friday, September 14, 2012
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Slide 35 text
@sandimetz Sept 2012
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
31
Friday, September 14, 2012
Slide 36
Slide 36 text
@sandimetz Sept 2012
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
31
Friday, September 14, 2012
Slide 37
Slide 37 text
@sandimetz Sept 2012
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
31
Friday, September 14, 2012
Slide 38
Slide 38 text
@sandimetz Sept 2012
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
31
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32
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Omega Mess
32
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Omega Mess
End of the Line
32
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Omega Mess
End of the Line
No Dependencies
32
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Omega Mess
End of the Line
No Dependencies
No Dependents
32
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@sandimetz Sept 2012
33
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@sandimetz Sept 2012
33
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@sandimetz Sept 2012
33
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@sandimetz Sept 2012
33
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@sandimetz Sept 2012
33
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@sandimetz Sept 2012
33
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@sandimetz Sept 2012
33
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@sandimetz Sept 2012
34
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@sandimetz Sept 2012
Knowledge Stability
34
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@sandimetz Sept 2012
External
Knowledge Stability
34
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@sandimetz Sept 2012
Internal
External
Knowledge Stability
34
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@sandimetz Sept 2012
Internal
External
Knowledge Stability Low
High
34
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@sandimetz Sept 2012
Internal
External
Knowledge Stability Low
High
34
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@sandimetz Sept 2012
Internal
External
Knowledge Stability Low
High
34
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@sandimetz Sept 2012
Internal
External
Knowledge Stability Low
High
34
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@sandimetz Sept 2012
Internal
External
Knowledge Stability Low
High
34
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@sandimetz Sept 2012
Internal
External
Knowledge Stability Low
High
34
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@sandimetz Sept 2012
Internal
External
Knowledge Stability Low
High
34
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@sandimetz Sept 2012
Dependencies
Shock
35
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@sandimetz Sept 2012
Dependencies
Shock
Game
35
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@sandimetz Sept 2012
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@sandimetz Sept 2012
Omega
36
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@sandimetz Sept 2012
Omega
36
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37
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Omega Mess
37
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Omega Mess
Hides behind
the message
37
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@sandimetz Sept 2012
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
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Friday, September 14, 2012
Slide 71
Slide 71 text
@sandimetz Sept 2012
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
38
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@sandimetz Sept 2012
39
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@sandimetz Sept 2012
It’s about
the message
39
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40
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41
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Interlude
42
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@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
43
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@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
43
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@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
43
Friday, September 14, 2012
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@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Public
API
43
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@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Public
API
Private
Behavior
43
Friday, September 14, 2012
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@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Public
API
Private
Behavior
Dependencies
43
Friday, September 14, 2012
Slide 83
Slide 83 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Public
API
Private
Behavior
Dependencies
Expose
43
Friday, September 14, 2012
Slide 84
Slide 84 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Public
API
Private
Behavior
Dependencies
Expose Hide
43
Friday, September 14, 2012
Slide 85
Slide 85 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Public
API
Private
Behavior
Dependencies
Expose Hide
Minimize
43
Friday, September 14, 2012
Slide 86
Slide 86 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Public
API
Private
Behavior
Dependencies
Expose Hide
Minimize Move
43
Friday, September 14, 2012
Slide 87
Slide 87 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
Game depends on
3. cost message
4. Shock class name
5. cost receiver
44
Friday, September 14, 2012
Slide 88
Slide 88 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
Game depends on
3. cost message
4. Shock class name
5. cost receiver
44
Friday, September 14, 2012
Slide 89
Slide 89 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
Game depends on
3. cost message
4. Shock class name
5. cost receiver
44
Friday, September 14, 2012
Slide 90
Slide 90 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
Game depends on
3. cost message
4. Shock class name
5. cost receiver
45
Friday, September 14, 2012
Slide 91
Slide 91 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
46
Friday, September 14, 2012
Slide 92
Slide 92 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
1
46
Friday, September 14, 2012
Slide 93
Slide 93 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method (expose)
2. cost calculation
Game depends on
3. cost message
4. Shock class name
5. cost receiver
47
Friday, September 14, 2012
Slide 94
Slide 94 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method (expose)
2. cost calculation
Game depends on
3. cost message
4. Shock class name
5. cost receiver
47
Friday, September 14, 2012
Slide 95
Slide 95 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
1
48
Friday, September 14, 2012
Slide 96
Slide 96 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
1
2
48
Friday, September 14, 2012
Slide 97
Slide 97 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method (expose)
2. cost calculation (hide)
Game depends on
3. cost message
4. Shock class name
5. cost receiver
49
Friday, September 14, 2012
Slide 98
Slide 98 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method (expose)
2. cost calculation (hide)
Game depends on
3. cost message
4. Shock class name
5. cost receiver
49
Friday, September 14, 2012
Slide 99
Slide 99 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method (expose)
2. cost calculation (hide)
Game depends on
3. cost message
4. Shock class name
5. cost receiver
49
Friday, September 14, 2012
Slide 100
Slide 100 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
50
Friday, September 14, 2012
Slide 101
Slide 101 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
3
50
Friday, September 14, 2012
Slide 102
Slide 102 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
Game depends on
3. cost message (minimize)
4. Shock class name
5. cost receiver
51
Friday, September 14, 2012
Slide 103
Slide 103 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
Game depends on
3. cost message (minimize)
4. Shock class name
5. cost receiver
51
Friday, September 14, 2012
Slide 104
Slide 104 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
3
52
Friday, September 14, 2012
Slide 105
Slide 105 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
4 5
3
52
Friday, September 14, 2012
Slide 106
Slide 106 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
4 5
3
52
Friday, September 14, 2012
Slide 107
Slide 107 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
?
Minimize Move
4 5
3
52
Friday, September 14, 2012
Slide 108
Slide 108 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
Game depends on
3. cost message (minimize)
4. Shock class name
5. cost receiver
???
53
Friday, September 14, 2012
Slide 109
Slide 109 text
@sandimetz Sept 2012
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
54
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Slide 110
Slide 110 text
@sandimetz Sept 2012
What is the
future cost of
doing nothing
now?
55
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Slide 111
Slide 111 text
@sandimetz Sept 2012
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
56
Friday, September 14, 2012
Slide 112
Slide 112 text
@sandimetz Sept 2012
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
56
Friday, September 14, 2012
Slide 113
Slide 113 text
@sandimetz Sept 2012
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
56
Friday, September 14, 2012
Slide 114
Slide 114 text
@sandimetz Sept 2012
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
56
Friday, September 14, 2012
Slide 115
Slide 115 text
57
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Slide 116
Slide 116 text
58
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Slide 117
Slide 117 text
@sandimetz Sept 2012
Example #2
Complicate the code
59
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Slide 118
Slide 118 text
@sandimetz Sept 2012
Example #2
Complicate the code
Shocks vary in cost
59
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Slide 119
Slide 119 text
@sandimetz Sept 2012
Example #2
class
Game
def
shock_cost(type)
Shock.new(type).cost
end
end
60
Friday, September 14, 2012
Slide 120
Slide 120 text
@sandimetz Sept 2012
Example #2
class
Game
def
shock_cost(type)
Shock.new(type).cost
end
end
60
Friday, September 14, 2012
Slide 121
Slide 121 text
@sandimetz Sept 2012
Example #2
class
Game
def
shock_cost(type)
Shock.new(type).cost
end
end
60
Friday, September 14, 2012
Slide 122
Slide 122 text
@sandimetz Sept 2012
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
61
Friday, September 14, 2012
Slide 123
Slide 123 text
@sandimetz Sept 2012
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
61
Friday, September 14, 2012
Slide 124
Slide 124 text
@sandimetz Sept 2012
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
61
Friday, September 14, 2012
Slide 125
Slide 125 text
@sandimetz Sept 2012
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
61
Friday, September 14, 2012
Slide 126
Slide 126 text
@sandimetz Sept 2012
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
61
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Slide 127
Slide 127 text
@sandimetz Sept 2012
62
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Slide 128
Slide 128 text
@sandimetz Sept 2012
62
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Slide 129
Slide 129 text
@sandimetz Sept 2012
Omega?
62
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Slide 130
Slide 130 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
3.
4.
63
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Slide 131
Slide 131 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. cost calculation
3.
4.
63
Friday, September 14, 2012
Slide 132
Slide 132 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
64
Friday, September 14, 2012
Slide 133
Slide 133 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
64
Friday, September 14, 2012
Slide 134
Slide 134 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
64
Friday, September 14, 2012
Slide 135
Slide 135 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
65
Friday, September 14, 2012
Slide 136
Slide 136 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
Omega
Mess?
66
Friday, September 14, 2012
Slide 137
Slide 137 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
Omega
Mess?
66
Friday, September 14, 2012
Slide 138
Slide 138 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
Meta
Knowledge
67
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Slide 139
Slide 139 text
68
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Slide 140
Slide 140 text
Meta Knowledge
68
Friday, September 14, 2012
Slide 141
Slide 141 text
Meta Knowledge
Knowledge
about
Knowledge
68
Friday, September 14, 2012
Slide 142
Slide 142 text
69
Friday, September 14, 2012
Slide 143
Slide 143 text
Meta Knowledge
69
Friday, September 14, 2012
Slide 144
Slide 144 text
Meta Knowledge
The
Domain of
Design
69
Friday, September 14, 2012
Slide 145
Slide 145 text
70
Friday, September 14, 2012
Slide 146
Slide 146 text
Interlude
71
Friday, September 14, 2012
Slide 147
Slide 147 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
72
Friday, September 14, 2012
Slide 148
Slide 148 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
72
Friday, September 14, 2012
Slide 149
Slide 149 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
72
Friday, September 14, 2012
Slide 150
Slide 150 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
2
73
Friday, September 14, 2012
Slide 151
Slide 151 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
2
73
Friday, September 14, 2012
Slide 152
Slide 152 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations (move)
3. four shock types
4. which type gets what calculation
74
Friday, September 14, 2012
Slide 153
Slide 153 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations (move)
3. four shock types
4. which type gets what calculation
74
Friday, September 14, 2012
Slide 154
Slide 154 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
75
Friday, September 14, 2012
Slide 155
Slide 155 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
3
75
Friday, September 14, 2012
Slide 156
Slide 156 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations (move)
3. four shock types (move)
4. which type gets what calculation
76
Friday, September 14, 2012
Slide 157
Slide 157 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations (move)
3. four shock types (move)
4. which type gets what calculation
76
Friday, September 14, 2012
Slide 158
Slide 158 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
77
Friday, September 14, 2012
Slide 159
Slide 159 text
@sandimetz Sept 2012
Knowledge Plot
Stable Unstable
Within My Purpose
Outside of My Purpose
Expose Hide
Minimize Move
4
77
Friday, September 14, 2012
Slide 160
Slide 160 text
@sandimetz Sept 2012
Knowledge
Shock knows
1. cost method
2. four shock cost calculations (move)
3. four shock types (move)
4. which type gets what calculation (min)
78
Friday, September 14, 2012
Slide 161
Slide 161 text
@sandimetz Sept 2012
Preference
79
Friday, September 14, 2012
Slide 162
Slide 162 text
@sandimetz Sept 2012
Preference
Send a message
79
Friday, September 14, 2012
Slide 163
Slide 163 text
@sandimetz Sept 2012
Preference
Send a message
rather than
implement behavior
79
Friday, September 14, 2012
Slide 164
Slide 164 text
@sandimetz Sept 2012
Move it
80
Friday, September 14, 2012
Slide 165
Slide 165 text
@sandimetz Sept 2012
Move it
Find the message
80
Friday, September 14, 2012
Slide 166
Slide 166 text
@sandimetz Sept 2012
Move it
Find the message
(Create the object)
80
Friday, September 14, 2012
Slide 167
Slide 167 text
@sandimetz Sept 2012
Move it
Find the message
(Create the object)
Send the message
80
Friday, September 14, 2012
Slide 168
Slide 168 text
81
Friday, September 14, 2012
Slide 169
Slide 169 text
@sandimetz Sept 2012
Example #3
Composition
82
Friday, September 14, 2012
Slide 170
Slide 170 text
@sandimetz Sept 2012
#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
83
Friday, September 14, 2012
Slide 171
Slide 171 text
@sandimetz Sept 2012
#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
83
Friday, September 14, 2012
Slide 172
Slide 172 text
@sandimetz Sept 2012
#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
83
Friday, September 14, 2012
Slide 173
Slide 173 text
@sandimetz Sept 2012
#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?
83
Friday, September 14, 2012
Slide 174
Slide 174 text
@sandimetz Sept 2012
#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
84
Friday, September 14, 2012
Slide 175
Slide 175 text
@sandimetz Sept 2012
#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
???
84
Friday, September 14, 2012
Slide 176
Slide 176 text
@sandimetz Sept 2012
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
85
Friday, September 14, 2012
Slide 177
Slide 177 text
@sandimetz Sept 2012
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
85
Friday, September 14, 2012
Slide 178
Slide 178 text
@sandimetz Sept 2012
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
85
Friday, September 14, 2012
Slide 179
Slide 179 text
@sandimetz Sept 2012
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
86
Friday, September 14, 2012
Slide 180
Slide 180 text
@sandimetz Sept 2012
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
86
Friday, September 14, 2012
Slide 181
Slide 181 text
@sandimetz Sept 2012
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
87
Friday, September 14, 2012
Slide 182
Slide 182 text
@sandimetz Sept 2012
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
87
Friday, September 14, 2012
Slide 183
Slide 183 text
@sandimetz Sept 2012
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
87
Friday, September 14, 2012
Slide 184
Slide 184 text
@sandimetz Sept 2012
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
87
Friday, September 14, 2012
Slide 185
Slide 185 text
@sandimetz Sept 2012
#3 Composition
class
FrontShockCost
def
compute
#
the
original
mess
end
end
class
RearShockCost
def
compute
#
slightly
changed
mess
end
end
#
etc
88
Friday, September 14, 2012
Slide 186
Slide 186 text
@sandimetz Sept 2012
#3 Composition
class
FrontShockCost
def
compute
#
the
original
mess
end
end
class
RearShockCost
def
compute
#
slightly
changed
mess
end
end
#
etc
88
Friday, September 14, 2012
Slide 187
Slide 187 text
@sandimetz Sept 2012
#3 Composition
class
FrontShockCost
def
compute
#
the
original
mess
end
end
class
RearShockCost
def
compute
#
slightly
changed
mess
end
end
#
etc
88
Friday, September 14, 2012
Slide 188
Slide 188 text
@sandimetz Sept 2012
#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
89
Friday, September 14, 2012
Slide 189
Slide 189 text
@sandimetz Sept 2012
#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
89
Friday, September 14, 2012
Slide 190
Slide 190 text
@sandimetz Sept 2012
#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
90
Friday, September 14, 2012
Slide 191
Slide 191 text
@sandimetz Sept 2012
#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
90
Friday, September 14, 2012
Slide 192
Slide 192 text
@sandimetz Sept 2012
#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?
90
Friday, September 14, 2012
Slide 193
Slide 193 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
91
Friday, September 14, 2012
Slide 194
Slide 194 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four shock cost calculations
3. four shock types
4. which type gets what calculation
91
Friday, September 14, 2012
Slide 195
Slide 195 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four ShockCostxx classes
3. four shock types
4. which type gets what calculation
92
Friday, September 14, 2012
Slide 196
Slide 196 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four ShockCostxx classes
3. four shock types
4. which type gets what calculation
93
Friday, September 14, 2012
Slide 197
Slide 197 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four ShockCostxx classes
3. four shock types
4. which type gets what class
94
Friday, September 14, 2012
Slide 198
Slide 198 text
@sandimetz Sept 2012
Good News
Calculations are isolated
95
Friday, September 14, 2012
Slide 199
Slide 199 text
@sandimetz Sept 2012
Bad News
Still have dependencies
96
Friday, September 14, 2012
Slide 200
Slide 200 text
@sandimetz Sept 2012
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
97
Friday, September 14, 2012
Slide 201
Slide 201 text
@sandimetz Sept 2012
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
97
Friday, September 14, 2012
Slide 202
Slide 202 text
@sandimetz Sept 2012
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
FrontShockCost.new.compute
#3 Composition
98
Friday, September 14, 2012
Slide 203
Slide 203 text
@sandimetz Sept 2012
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
98
Friday, September 14, 2012
Slide 204
Slide 204 text
@sandimetz Sept 2012
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
98
Friday, September 14, 2012
Slide 205
Slide 205 text
@sandimetz Sept 2012
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
Convention over con guration
98
Friday, September 14, 2012
Slide 206
Slide 206 text
@sandimetz Sept 2012
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.titleize
+
"ShockCost"
#3 Composition
Convention over con guration
98
Friday, September 14, 2012
Slide 207
Slide 207 text
@sandimetz Sept 2012
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.titleize
+
"ShockCost"
eval(class_name).new.compute
#3 Composition
Convention over con guration
when
:foo
FooShockCost.new.compute
99
Friday, September 14, 2012
Slide 208
Slide 208 text
@sandimetz Sept 2012
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.titleize
+
"ShockCost"
eval(class_name).new.compute
Object.const_get(class_name).new.compute
#3 Composition
Convention over con guration
when
:foo
FooShockCost.new.compute
100
Friday, September 14, 2012
Slide 209
Slide 209 text
@sandimetz Sept 2012
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.titleize
+
"ShockCost"
eval(class_name).new.compute
Object.const_get(class_name).new.compute
class_name.constantize.new.compute
#3 Composition
Convention over con guration
when
:foo
FooShockCost.new.compute
101
Friday, September 14, 2012
Slide 210
Slide 210 text
@sandimetz Sept 2012
Example #3
class
Shock
def
cost(type)
class_name
=
(type.to_s.titleize
+
"ShockCost")
class_name.constantize.new.compute
end
end
102
Friday, September 14, 2012
Slide 211
Slide 211 text
@sandimetz Sept 2012
Example #3
class
Shock
def
cost(type)
class_name
=
(type.to_s.titleize
+
"ShockCost")
class_name.constantize.new.compute
end
end
102
Friday, September 14, 2012
Slide 212
Slide 212 text
@sandimetz Sept 2012
Example #3
class
Shock
def
cost(type)
class_name
=
(type.to_s.titleize
+
"ShockCost")
class_name.constantize.new.compute
end
end
Factory
102
Friday, September 14, 2012
Slide 213
Slide 213 text
@sandimetz Sept 2012
We
<3
Factories
103
Friday, September 14, 2012
Slide 214
Slide 214 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four ShockCostxx classes
3. four shock types
4. which type gets what class
104
Friday, September 14, 2012
Slide 215
Slide 215 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four ShockCostxx classes
3. four shock types
4. which type gets what class
104
Friday, September 14, 2012
Slide 216
Slide 216 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four ShockCostxx classes
3. four shock types
4. which type gets what class
104
Friday, September 14, 2012
Slide 217
Slide 217 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. four ShockCostxx classes
3. four shock types
4. which type gets what class
104
Friday, September 14, 2012
Slide 218
Slide 218 text
@sandimetz Sept 2012
Meta Knowledge
Shock knows
1. cost method
2. the convention
105
Friday, September 14, 2012
Slide 219
Slide 219 text
@sandimetz Sept 2012
Before
#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
106
Friday, September 14, 2012
Slide 220
Slide 220 text
@sandimetz Sept 2012
Before
#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
106
Friday, September 14, 2012
Slide 221
Slide 221 text
@sandimetz Sept 2012
After
Example #3
class
Shock
def
cost(type)
class_name
=
(type.to_s.titleize
+
"ShockCost")
class_name.constantize.new.compute
end
end
107
Friday, September 14, 2012
Slide 222
Slide 222 text
@sandimetz Sept 2012
After
Example #3
class
Shock
def
cost(type)
to_class(type).new.compute
end
def
to_class(type)
(type.to_s.titleize
+
"ShockCost").constantize
end
end
108
Friday, September 14, 2012
Slide 223
Slide 223 text
@sandimetz Sept 2012
After
Example #3
class
Shock
def
cost(type)
to_class(type).new.compute
end
def
to_class(type)
(type.to_s.titleize
+
"ShockCost").constantize
end
end
Few changes
affect this code
109
Friday, September 14, 2012
Slide 224
Slide 224 text
@sandimetz Sept 2012
After
Example #3
class
FrontShockCost
def
compute
#
the
original
mess
end
end
class
Shock
def
cost(type)
to_class(type).new.compute
end
def
to_class(type)
(type.to_s.titleize
+
"ShockCost").constantize
end
end
Few changes
affect this code
109
Friday, September 14, 2012
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@sandimetz Sept 2012
After
Example #3
class
FrontShockCost
def
compute
#
the
original
mess
end
end
class
Shock
def
cost(type)
to_class(type).new.compute
end
def
to_class(type)
(type.to_s.titleize
+
"ShockCost").constantize
end
end
class
RearShockCost
def
compute
#
slightly
changed
mess
end
end
Few changes
affect this code
109
Friday, September 14, 2012
Slide 226
Slide 226 text
@sandimetz Sept 2012
After
Example #3
class
FrontShockCost
def
compute
#
the
original
mess
end
end
class
Shock
def
cost(type)
to_class(type).new.compute
end
def
to_class(type)
(type.to_s.titleize
+
"ShockCost").constantize
end
end
class
RearShockCost
def
compute
#
slightly
changed
mess
end
end
Etc...
Few changes
affect this code
109
Friday, September 14, 2012
Slide 227
Slide 227 text
@sandimetz Sept 2012
After
Example #3
class
FrontShockCost
def
compute
#
the
original
mess
end
end
class
Shock
def
cost(type)
to_class(type).new.compute
end
def
to_class(type)
(type.to_s.titleize
+
"ShockCost").constantize
end
end
class
RearShockCost
def
compute
#
slightly
changed
mess
end
end
Etc...
Few changes
affect this code
Need a new one?
Follow the
convention!
109
Friday, September 14, 2012
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@sandimetz Sept 2012
Composition
110
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@sandimetz Sept 2012
Shock
?
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@sandimetz Sept 2012
Shock
111
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@sandimetz Sept 2012
Shock
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@sandimetz Sept 2012
Shock
112
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@sandimetz Sept 2012
Shock
113
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@sandimetz Sept 2012
Shock
114
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@sandimetz Sept 2012
Shock
115
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@sandimetz Sept 2012
Shock
115
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@sandimetz Sept 2012
Shock
116
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@sandimetz Sept 2012
Shock
116
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@sandimetz Sept 2012
The Role
117
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@sandimetz Sept 2012
118
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@sandimetz Sept 2012
118
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@sandimetz Sept 2012
Reprise
Find the message
(Create the object)
Send the message
119
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@sandimetz Sept 2012
Omega Mess
120
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@sandimetz Sept 2012
Omega Mess
Hide It
120
Friday, September 14, 2012
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@sandimetz Sept 2012
Meta Knowledge
121
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@sandimetz Sept 2012
Meta Knowledge
Organize It
121
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122
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123
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124
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Depend on Stability
125
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Depend on Stability
Find the Message
126
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Slide 252 text
Isolate Uncertainty
127
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Isolate Uncertainty
Hide the Mess
128
Friday, September 14, 2012
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We Stand on the
Shoulders of Giants
129
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Slide 255 text
130
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131
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132
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133
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134
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135
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Thanks
Sandi Metz
136
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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
137
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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
138
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http://bit.ly/
poodr-combo
139
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Hot
off
the
press
http://bit.ly/
poodr-combo
139
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Questions?
140
Friday, September 14, 2012