all the little things (railsconf)

@sandimetz Apr 2014
sandi metz
all the little things
1
Thursday, April 24, 14

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@sandimetz Apr 2014
Want better apps?
2

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@sandimetz Apr 2014
make smaller things
3

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@sandimetz Apr 2014
The Gilded Rose Kata
4

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@sandimetz Apr 2014
class GildedRose
attr_reader :name, :quality, :days_remaining
def initialize(name, quality, days_remaining)
@name, @quality, @days_remaining = name, quality, days_remaining
end
def tick
# ...
end
end
5

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@sandimetz Apr 2014
def tick
if @name != 'Aged Brie' && @name != 'Backstage passes to a TAFKAL80ETC c
if @quality > 0
if @name != 'Sulfuras, Hand of Ragnaros'
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @name == 'Backstage passes to a TAFKAL80ETC concert'
if @days_remaining < 11
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
# 21 more lines
def tick
if name != 'Aged Brie' && name != 'Backstage passes to a TAFKAL80ETC concert'
if quality > 0
if name != 'Sulfuras, Hand of Ragnaros'
@quality -‐= 1
end
end
else
if quality < 50
@quality += 1
if name == 'Backstage passes to a TAFKAL80ETC concert'
if days_remaining < 11
if quality < 50
@quality += 1
end
end
if quality < 50
@quality += 1
end
end
end
end
end
@days_remaining -‐= 1
end
if name != "Aged Brie"
if name != 'Backstage passes to a TAFKAL80ETC concert'
if quality > 0
@quality -‐= 1
end
end
else
@quality = quality -‐ quality
end
else
if quality < 50
@quality += 1
end
end
end
end
end
6

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@sandimetz Apr 2014
def tick
# 22 previous lines
end
if @name != "Aged Brie"
if @name != 'Backstage passes to a TAFKAL80ETC concert'
if @quality > 0
@quality -‐= 1
end
end
else
@quality = @quality -‐ @quality
end
else
if @quality < 50
@quality += 1
end
end
end
end
def tick
if quality > 0
@quality -‐= 1
end
end
else
if quality < 50
@quality += 1
if quality < 50
@quality += 1
end
end
if quality < 50
@quality += 1
end
end
end
end
end
end
if quality > 0
@quality -‐= 1
end
end
else
end
else
if quality < 50
@quality += 1
end
end
end
end
end
7

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@sandimetz Apr 2014
def tick
if @name != 'Aged Brie' && @name != 'Backstage passes to a TAFKAL80ETC concert'
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
8

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
44.7
0
25
50
big conditional
Complexity (Flog)
9

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
44.7
0
25
50
big conditional
Complexity (Flog)
50
9

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
44.7
0
25
50
big conditional
Complexity (Flog)
45
tick
50
9

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
10

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@sandimetz Apr 2014
11

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
12

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
Squint Test
12

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
changes in shape
13

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
2
14

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
changes in color
15

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
16

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
17

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
16 if statements
17

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
16 if statements
7 !=
17

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
16 if statements
7 !=
2 != with &&
17

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
16 if statements
7 !=
2 != with &&
3 magic strings
17

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
16 if statements
7 !=
2 != with &&
3 magic strings
? magic numbers
17

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
magic strings
18

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
‘Aged Brie’
magic strings
18

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
‘Aged Brie’
‘Sulfuras, Hand of Ragnaros’
magic strings
18

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
‘Aged Brie’
‘Sulfuras, Hand of Ragnaros’
‘Backstage passes
to a TAFKAL80ETC concert’
magic strings
18

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
it has tests
19

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@sandimetz Apr 2014
# Running:
S..S.S...S..........S....S.....
Fabulous run in 0.002800s, 11071.4286 runs/s, 17857.1429 assertions/s.
31 runs, 50 assertions, 0 failures, 0 errors, 6 skips
20

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@sandimetz Apr 2014
class GildedRoseTest < Minitest::Test
def test_normal_item_before_sell_date
def test_normal_item_on_sell_date
def test_normal_item_after_sell_date
def test_normal_item_of_zero_quality
def test_brie_before_sell_date
def test_brie_before_sell_date_with_max_quality
def test_brie_on_sell_date
def test_brie_on_sell_date_near_max_quality
def test_brie_on_sell_date_with_max_quality
def test_brie_after_sell_date
def test_brie_after_sell_date_with_max_quality
def test_sulfuras_before_sell_date
def test_sulfuras_on_sell_date
def test_sulfuras_after_sell_date
def test_backstage_pass_long_before_sell_date
def test_backstage_pass_medium_close_to_sell_date_upper_bound
def test_backstage_pass_medium_close_to_sell_date_upper_bound_at_max_quality
def test_backstage_pass_medium_close_to_sell_date_lower_bound
def test_backstage_pass_medium_close_to_sell_date_lower_bound_at_max_quality
def test_backstage_pass_very_close_to_sell_date_upper_bound
def test_backstage_pass_very_close_to_sell_date_upper_bound_at_max_quality
def test_backstage_pass_very_close_to_sell_date_lower_bound
def test_backstage_pass_very_close_to_sell_date_lower_bound_at_max_quality
def test_backstage_pass_on_sell_date
def test_backstage_pass_after_sell_date
21

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@sandimetz Apr 2014
brie
21

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@sandimetz Apr 2014
brie
sulfuras
21

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@sandimetz Apr 2014
brie
sulfuras
backstage pass
21

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@sandimetz Apr 2014
brie
sulfuras
backstage pass
normal
21

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@sandimetz Apr 2014
item = GildedRose.new('normal', 10, 5)
item.tick
assert_equal 9, item.quality
assert_equal 4, item.days_remaining
end
let’s look at a test
22

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@sandimetz Apr 2014
item.tick
end
23

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@sandimetz Apr 2014
item.tick
end
name
23

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@sandimetz Apr 2014
item.tick
end
name
quality
23

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@sandimetz Apr 2014
item.tick
end
name
quality
days_remaining
23

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@sandimetz Apr 2014
item.tick
end
23

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@sandimetz Apr 2014
item.tick
end
reduced by 1
24

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@sandimetz Apr 2014
def test_conjured_item_before_sell_date
def test_conjured_item_at_zero_quality
def test_conjured_item_on_sell_date
def test_conjured_item_on_sell_date_at_zero_quality
def test_conjured_item_after_sell_date
def test_conjured_item_after_sell_date_at_zero_quality
end
25

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@sandimetz Apr 2014
end
6 skipped tests
25

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@sandimetz Apr 2014
end
26

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@sandimetz Apr 2014
27

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@sandimetz Apr 2014
Task:
27

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@sandimetz Apr 2014
Task:
Implement Conjured
27

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@sandimetz Apr 2014
end
28

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@sandimetz Apr 2014
end
I tried
28

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@sandimetz Apr 2014
end
but failed
29

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@sandimetz Apr 2014
end
miserably
30

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@sandimetz Apr 2014
the pattern failed me
31

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@sandimetz Apr 2014
32

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@sandimetz Apr 2014
Task:
32

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@sandimetz Apr 2014
Task:
Refactor code so I can
Implement Conjured
32

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@sandimetz Apr 2014
normal
33

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
# ....
def tick
if quality > 0
@quality -‐= 1
end
end
else
if quality < 50
@quality += 1
if quality < 50
@quality += 1
end
end
if quality < 50
@quality += 1
end
end
end
end
end
end
if quality > 0
@quality -‐= 1
end
end
else
end
else
if quality < 50
@quality += 1
end
end
end
end
end
34

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@sandimetz Apr 2014
def tick
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
def tick
if name == 'normal'
return
end
if quality > 0
@quality -‐= 1
end
end
else
if quality < 50
@quality += 1
if quality < 50
@quality += 1
end
end
if quality < 50
@quality += 1
end
end
end
end
end
end
if quality > 0
@quality -‐= 1
end
end
else
end
else
if quality < 50
@quality += 1
end
end
end
end
end
35

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@sandimetz Apr 2014
def tick
if name == 'normal'
return
end
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
def tick
if name == 'normal'
return
end
if quality > 0
@quality -‐= 1
end
end
else
if quality < 50
@quality += 1
if quality < 50
@quality += 1
end
end
if quality < 50
@quality += 1
end
end
end
end
end
end
if quality > 0
@quality -‐= 1
end
end
else
end
else
if quality < 50
@quality += 1
end
end
end
end
end
36

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@sandimetz Apr 2014
# Running:
.S...S...S..SFF....F.....SS.F..
1) Failure:
GildedRoseTest#test_normal_item_of_zero_quality [gilded_rose_test.rb:37]:
Expected: 4
Actual: 5
2) Failure:
GildedRoseTest#test_normal_item_before_sell_date [gilded_rose_test.rb:12]:
Expected: 9
Actual: 10
3) Failure:
GildedRoseTest#test_normal_item_on_sell_date [gilded_rose_test.rb:20]:
Expected: 8
Actual: 10
4) Failure:
GildedRoseTest#test_normal_item_after_sell_date [gilded_rose_test.rb:28]:
Expected: 8
Actual: 10
37

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@sandimetz Apr 2014
# Running:
.S...S...S..SFF....F.....SS.F..
1) Failure:
Expected: 4
Actual: 5
2) Failure:
Expected: 9
Actual: 10
3) Failure:
Expected: 8
Actual: 10
4) Failure:
Expected: 8
Actual: 10
4 failures
37

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@sandimetz Apr 2014
class GildedRose
def tick
if name == 'normal'
return
end
if @quality > 0
# ... 40 more lines
end
end
38

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@sandimetz Apr 2014
class GildedRose
def tick
if name == 'normal'
return
end
if @quality > 0
# ... 40 more lines
end
def normal_tick
end
end
39

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@sandimetz Apr 2014
class GildedRose
def tick
if name == 'normal'
return normal_tick
end
if @quality > 0
# ... 40 more lines
end
def normal_tick
end
end
40

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@sandimetz Apr 2014
# Running:
.S...S...S..SFF....F.....SS.F..
1) Failure:
Expected: 4
Actual: 5
2) Failure:
Expected: 9
Actual: 10
3) Failure:
Expected: 8
Actual: 10
4) Failure:
Expected: 8
Actual: 10
4 failures
41

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@sandimetz Apr 2014
item.tick
end
42

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@sandimetz Apr 2014
item.tick
end
class GildedRose
# ...
def normal_tick
end
end
43

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@sandimetz Apr 2014
item.tick
end
class GildedRose
# ...
def normal_tick
@quality -‐= 1
end
end
44

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@sandimetz Apr 2014
# Running:
.....S...FS....FS.S...FS....S..
1) Failure:
Expected: 0
Actual: -‐1
2) Failure:
Expected: 8
Actual: 9
3) Failure:
Expected: 8
Actual: 9
3 failures
45

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@sandimetz Apr 2014
item.tick
assert_equal -‐1, item.days_remaining
end
class GildedRose
# ...
def normal_tick
@quality -‐= 1
end
end
46

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@sandimetz Apr 2014
item.tick
end
class GildedRose
# ...
def normal_tick
@quality -‐= 1
end
end
47

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@sandimetz Apr 2014
item.tick
end
class GildedRose
# ...
def normal_tick
if @days_remaining > 0
@quality -‐= 1
end
end
end
48

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@sandimetz Apr 2014
item.tick
end
class GildedRose
# ...
def normal_tick
@quality -‐= 1
end
if @days_remaining <= 0
@quality -‐= 2
end
end
end
49

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@sandimetz Apr 2014
# Running:
...S.S.....S..S..SF.....S......
1) Failure:
Expected: 0
Actual: -‐1
1 failure ??
50

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@sandimetz Apr 2014
item.tick
end
class GildedRose
# ...
def normal_tick
@quality -‐= 1
end
@quality -‐= 2
end
end
end
51

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@sandimetz Apr 2014
item.tick
end
class GildedRose
# ...
def normal_tick
@quality -‐= 1
end
@quality -‐= 2
end
end
end
52

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@sandimetz Apr 2014
item.tick
end
class GildedRose
# ...
def normal_tick
if @quality != 0
@quality -‐= 1
end
@quality -‐= 2
end
end
end
end
53

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@sandimetz Apr 2014
# Running:
S..S.S...S..........S....S.....
54

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@sandimetz Apr 2014
refactor under green
55

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@sandimetz Apr 2014
reach for the
lowest hanging green
56

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@sandimetz Apr 2014
def normal_tick
if @quality != 0
@quality -‐= 1
end
@quality -‐= 2
end
end
end
57

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@sandimetz Apr 2014
def normal_tick
end
def normal_tick
if @quality != 0
@quality -‐= 1
end
@quality -‐= 2
end
end
end
58

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@sandimetz Apr 2014
def normal_tick
end
def normal_tick
if @quality != 0
@quality -‐= 1
end
@quality -‐= 2
end
end
end
59

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@sandimetz Apr 2014
def normal_tick
end
def normal_tick
if @quality != 0
@quality -‐= 1
end
@quality -‐= 2
end
end
end
60

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@sandimetz Apr 2014
def normal_tick
return if @quality == 0
end
def normal_tick
if @quality != 0
@quality -‐= 1
end
@quality -‐= 2
end
end
end
61

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@sandimetz Apr 2014
def normal_tick
end
def normal_tick
@quality -‐= 1
end
@quality -‐= 2
end
end
62

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@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def normal_tick
@quality -‐= 1
end
@quality -‐= 2
end
end
63

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@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
@quality -‐= 1 if @days_remaining <= 0
end
def normal_tick
@quality -‐= 1
end
@quality -‐= 2
end
end
64

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@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def normal_tick
end
65

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@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
66

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@sandimetz Apr 2014
# Running:
S..S.S...S..........S....S.....
67

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@sandimetz Apr 2014
class GildedRose
def tick
if name == 'normal'
return normal_tick
end
if @quality > 0
# ... 40 more lines
end
end
Reprise
68

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@sandimetz Apr 2014
class GildedRose
def tick
if name == 'normal'
return normal_tick
end
if @quality > 0
# ... 40 more lines
end
end
69

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@sandimetz Apr 2014
class GildedRose
def tick
if name == 'normal'
return normal_tick
end
if @quality > 0
# ... 40 more lines
end
def normal_tick
@quality -‐= 1
end
end
70

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@sandimetz Apr 2014
class GildedRose
def tick
if name == 'normal'
return normal_tick
end
if @quality > 0
# ... 40 more lines
end
def normal_tick
@quality -‐= 1
end
end
normal
70

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@sandimetz Apr 2014
# def test_normal ... etc
# def test_sulfuras ... etc
# def test_backstage ... etc
end
brie
71

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@sandimetz Apr 2014
def tick
if name == 'normal'
return normal_tick
end
# ...
end
72

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
end
# ...
end
73

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
74

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def brie_tick
end
75

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@sandimetz Apr 2014
# Running:
.F...F.....S.S.F..S.FF.S.F.FS.S
1) Failure:
GildedRoseTest#test_brie_on_sell_date_with_max_quality [gilded_rose_test.rb:78]:
Expected: 4
Actual: 5
2) Failure:
GildedRoseTest#test_brie_on_sell_date_near_max_quality [gilded_rose_test.rb:69]:
Expected: 50
Actual: 49
3) Failure:
GildedRoseTest#test_brie_on_sell_date [gilded_rose_test.rb:61]:
Expected: 12
Actual: 10
4) Failure:
GildedRoseTest#test_brie_after_sell_date_with_max_quality [gilded_rose_test.rb:94]:
Expected: -‐11
Actual: -‐10
5) Failure:
GildedRoseTest#test_brie_before_sell_date_with_max_quality [gilded_rose_test.rb:54]:
Expected: 6
Actual: 7
7 failures
76

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def brie_tick
end
77

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def brie_tick
end
fast forward...
77

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def brie_tick
return if @quality >= 50
@quality += 1
@quality += 1 if @days_remaining <= 0
end
78

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def brie_tick
@quality += 1
end
brie
78

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@sandimetz Apr 2014
# Running:
...S......S.....SS.....SS......
79

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@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
Similarity
80

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@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
81

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@sandimetz Apr 2014
duplication is far cheaper
than the wrong abstraction
82

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@sandimetz Apr 2014
# def test_brie ... etc
# def test_backstage ... etc
end
sulfuras
83

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
when 'Sulfuras, Hand of Ragnaros'
return sulfuras_tick
end
# ...
end
def sulfuras_tick
end
84

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@sandimetz Apr 2014
# Running:
...S......S.....SS.....SS......
0 failures ?!?
85

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def sulfuras_tick
end
86

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def sulfuras_tick
end
nothing changes
86

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def sulfuras_tick
end
sulfuras
86

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@sandimetz Apr 2014
# def test_brie ... etc
# def test_sulfuras ... etc
end
backstage
87

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@sandimetz Apr 2014
def tick
case name
when 'normal'
when 'Aged Brie'
when 'Backstage passes to a TAFKAL80ETC concert'
return backstage_tick
end
# ...
end
def backstage_tick
return @quality = 0 if @days_remaining < 0
@quality += 1
@quality += 1 if @days_remaining < 10
end
backstage
88

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@sandimetz Apr 2014
# Running:
...S......S.....SS.....SS......
89

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@sandimetz Apr 2014
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
# ...
end
def normal_tick
@quality -‐= 1
end
def brie_tick
def sulfuras_tick
def backstage_tick
class GildedRose
@name, @quality, @days_remaining = name, quality, days_remai
end
def tick
case name
when 'normal'
return normal_tick
when 'Aged Brie'
return brie_tick
end
if name != 'Aged Brie' && name != 'Backstage passes to a TAF
if quality > 0
@quality -‐= 1
end
end
else
if quality < 50
@quality += 1
if quality < 50
@quality += 1
end
end
if quality < 50
@quality += 1
end
end
end
end
end
end
if quality > 0
@quality -‐= 1
end
end
else
end
else
if quality < 50
@quality += 1
end
end
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
90

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@sandimetz Apr 2014
# Running:
...S......S.....SS.....SS......
91

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@sandimetz Apr 2014
small methods are simple
92

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@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
small methods
93

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@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
class GildedRose
end
def tick
if @name != 'Aged Brie' && @name != 'Backstage passes to a TAFKAL80ETC
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
end
big conditional small methods
94

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@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
0
25
50
big conditional
Total Complexity
50
95

View Slide

@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
0
25
50
tick normal brie backstage other
40
Total Complexity
50
96

View Slide

@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
0
25
50
tick normal brie backstage other
12
40
45
Total Complexity
50
96

View Slide

@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
Complexity
50
big conditional
97

View Slide

@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
0
45
90
Complexity
50
big conditional
97

View Slide

@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
0
45
90
Complexity
50
84
40
small methods
big conditional 10 Refactorings
97

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@sandimetz Apr 2014
Task:
Implement Conjured
98

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@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
99

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
99

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
def brie_tick
99

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
def brie_tick
def sulfuras_tick
99

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
def brie_tick
def sulfuras_tick
def backstage_tick
99

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
def brie_tick
def sulfuras_tick
def backstage_tick
def conjured_tick
99

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
def brie_tick
def sulfuras_tick
def backstage_tick
def conjured_tick
???
99

View Slide

@sandimetz Apr 2014
the pattern still fails me
100

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@sandimetz Apr 2014
open / closed
101

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@sandimetz Apr 2014
open for extension
102

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@sandimetz Apr 2014
open for extension
closed for modiﬁcation
103

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@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
def brie_tick
def sulfuras_tick
def backstage_tick
104

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@sandimetz Apr 2014
OO Principles
105

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@sandimetz Apr 2014
OO Principles
a style guide for
arranging code
106

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
def brie_tick
def sulfuras_tick
def backstage_tick
107

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@sandimetz Apr 2014
they’re screaming to get out
108

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
def normal_tick
def brie_tick
def sulfuras_tick
def backstage_tick
109

View Slide

@sandimetz Apr 2014
brie_tick
backstage_tick
sulfuras_tick
normal_tick
GildedRose
110

View Slide

@sandimetz Apr 2014
Normal
brie_tick
backstage_tick
sulfuras_tick
normal_tick
GildedRose
111

View Slide

@sandimetz Apr 2014
tick
Normal
brie_tick
backstage_tick
sulfuras_tick
normal_tick
GildedRose
112

View Slide

@sandimetz Apr 2014
tick
Normal
brie_tick
backstage_tick
sulfuras_tick
normal_tick
GildedRose
113

View Slide

@sandimetz Apr 2014
tick
Normal
brie_tick
backstage_tick
sulfuras_tick
GildedRose
114

View Slide

@sandimetz Apr 2014
tick
Normal
GildedRose
brie_tick
backstage_tick
sulfuras_tick
115

View Slide

@sandimetz Apr 2014
tick
Normal
GildedRose
brie_tick
backstage_tick
sulfuras_tick
116

View Slide

@sandimetz Apr 2014
def normal_tick
@quality -‐= 1
end
117

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@sandimetz Apr 2014
def tick
@quality -‐= 1
end
118

View Slide

@sandimetz Apr 2014
class Normal
def tick
@quality -‐= 1
end
end
119

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@sandimetz Apr 2014
class Normal
def initialize(quality, days_remaining)
@quality, @days_remaining = quality, days_remaining
end
def tick
@quality -‐= 1
end
end
120

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@sandimetz Apr 2014
class Normal
attr_reader :quality, :days_remaining
end
def tick
@quality -‐= 1
end
end
121

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@sandimetz Apr 2014

class Normal
end
def tick
@quality -‐= 1
end
end
122

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@sandimetz Apr 2014
class GildedRose
def normal_tick
end
class Normal
end
def tick
@quality -‐= 1
end
end
123

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@sandimetz Apr 2014
class GildedRose
def normal_tick
@item = Normal.new(quality, days_remaining)
end
class Normal
end
def tick
@quality -‐= 1
end
end
124

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@sandimetz Apr 2014
class GildedRose
def normal_tick
item.tick
end
class Normal
end
def tick
@quality -‐= 1
end
end
125

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@sandimetz Apr 2014
tick
Normal
GildedRose
brie_tick
backstage_tick
sulfuras_tick
126

View Slide

@sandimetz Apr 2014
normal is an object
127

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@sandimetz Apr 2014
brie/sulfuras/backstage are not
128

View Slide

@sandimetz Apr 2014
class GildedRose
def normal_tick
item.tick
end
129

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@sandimetz Apr 2014
class GildedRose
def normal_tick
item.tick
end
def brie_tick
@quality += 1
end
130

View Slide

@sandimetz Apr 2014
class GildedRose
def normal_tick
item.tick
end
def brie_tick
@quality += 1
end
def quality
end
def days_remaining
end
131

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@sandimetz Apr 2014
class GildedRose
def normal_tick
item.tick
end
def brie_tick
@quality += 1
end
def quality
return item.quality if item
end
def days_remaining
end
132

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@sandimetz Apr 2014
class GildedRose
def normal_tick
item.tick
end
def brie_tick
@quality += 1
end
def quality
@quality
end
def days_remaining
end
133

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@sandimetz Apr 2014
class GildedRose
def normal_tick
item.tick
end
def brie_tick
@quality += 1
end
def quality
@quality
end
def days_remaining
return item.days_remaining if item
@days_remaining
end
134

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@sandimetz Apr 2014
brie
135

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@sandimetz Apr 2014
class GildedRose
def brie_tick
@quality += 1
end
136

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@sandimetz Apr 2014
class GildedRose
def brie_tick
@quality += 1
end
class Brie
end
137

View Slide

@sandimetz Apr 2014
class GildedRose
def brie_tick
@quality += 1
end
class Brie
def tick
end
end
138

View Slide

@sandimetz Apr 2014
class GildedRose
def brie_tick
end
class Brie
def tick
@quality += 1
end
end
139

View Slide

@sandimetz Apr 2014
class GildedRose
def brie_tick
end
class Brie
end
def tick
@quality += 1
end
end
140

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@sandimetz Apr 2014
class GildedRose
def brie_tick
@item = Brie.new(quality, days_remaining)
item.tick
end
class Brie
end
def tick
@quality += 1
end
end
141

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@sandimetz Apr 2014
sulfuras
142

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@sandimetz Apr 2014
class GildedRose
def sulfuras_tick
end
143

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@sandimetz Apr 2014
class GildedRose
def sulfuras_tick
end
class Sulfuras
end
def tick
end
end
144

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@sandimetz Apr 2014
class GildedRose
def sulfuras_tick
end
class Sulfuras
end
def tick
end
end
145

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@sandimetz Apr 2014
class GildedRose
def sulfuras_tick
@item = Sulfuras.new(quality, days_remaining)
item.tick
end
class Sulfuras
end
def tick
end
end
146

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@sandimetz Apr 2014
backstage
147

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@sandimetz Apr 2014
class GildedRose
def backstage_tick
@quality += 1
end
148

View Slide

@sandimetz Apr 2014
class GildedRose
def backstage_tick
@quality += 1
end
class Backstage
def tick
end
149

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@sandimetz Apr 2014
class GildedRose
def backstage_tick
end
class Backstage
def tick
@quality += 1
end
150

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@sandimetz Apr 2014
class GildedRose
def backstage_tick
end
class Backstage
end
def tick
@quality += 1
end
151

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@sandimetz Apr 2014
class GildedRose
def backstage_tick
end
class Backstage
end
def tick
@quality += 1
end
152

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@sandimetz Apr 2014
class GildedRose
def backstage_tick
end
class Backstage
end
def tick
@quality += 1
end
153

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@sandimetz Apr 2014
class GildedRose
def backstage_tick
@item = Backstage.new(quality, days_remaining)
item.tick
end
class Backstage
end
def tick
@quality += 1
end
154

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@sandimetz Apr 2014
normal/brie/sulfuras/backstage
are now objects
155

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@sandimetz Apr 2014
GildedRose
tick
Normal
tick
Brie
tick
Sulfuras
attr_reader :item
tick
Backstage
attr_reader
:quality,
:days_remaining
156

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
item.tick
end
def brie_tick
item.tick
end
# etc
157

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@sandimetz Apr 2014
rewind
158

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
item.tick
end
def brie_tick
item.tick
end
# etc
159

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
item.tick
end
def brie_tick
item.tick
end
# etc
160

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
item.tick
end
def brie_tick
item.tick
end
# etc
161

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
end
def brie_tick
item.tick
end
# etc
162

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def brie_tick
item.tick
end
# etc
163

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def brie_tick
item.tick
end
# etc
164

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
end
end
def brie_tick
item.tick
end
# etc
165

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
item.tick
item.tick
item.tick
end
end
166

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@sandimetz Apr 2014
abstract away the duplication
167

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
item.tick
item.tick
item.tick
end
end
168

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@sandimetz Apr 2014
class GildedRose
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
item.tick
item.tick
item.tick
end
end
169

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@sandimetz Apr 2014
class GildedRose
attr_reader :name, :item
end
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
item.tick
item.tick
item.tick
end
end
170

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@sandimetz Apr 2014
class GildedRose
@item = ???
end
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
item.tick
item.tick
item.tick
end
end
171

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@sandimetz Apr 2014
class GildedRose
@item = ???.new(quality, days_remaining)
end
def tick
case name
when 'normal'
item.tick
when 'Aged Brie'
item.tick
item.tick
item.tick
end
end
172

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@sandimetz Apr 2014
class GildedRose
end
def
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Sulfuras
Backstage
end
173

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@sandimetz Apr 2014
class GildedRose
end
def
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Sulfuras
Backstage
end
end
174

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@sandimetz Apr 2014
class GildedRose
end
def klass_for(name)
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Sulfuras
Backstage
end
end
175

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@sandimetz Apr 2014
class GildedRose
@item = klass_for(name).new(quality, days_remaining)
end
def klass_for(name)
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Sulfuras
Backstage
end
end
176

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@sandimetz Apr 2014
class GildedRose
attr_reader :item
end
def klass_for(name)
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Sulfuras
Backstage
end
end
177

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@sandimetz Apr 2014
class GildedRose
attr_reader :item
end
def klass_for(name)
# ...
end
178

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@sandimetz Apr 2014
class GildedRose
attr_reader :item
end
def klass_for(name)
# ...
end
def tick
item.tick
end
179

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@sandimetz Apr 2014
class GildedRose
attr_reader :item
end
def klass_for(name)
# ...
end
def tick
item.tick
end
def quality
@quality
end
def days_remaining
@days_remaining
end
180

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@sandimetz Apr 2014
class GildedRose
attr_reader :item
end
def klass_for(name)
# ...
end
def tick
item.tick
end
def quality
end
def days_remaining
end
181

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@sandimetz Apr 2014
class GildedRose
attr_reader :item
end
def klass_for(name)
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
182

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@sandimetz Apr 2014
class GildedRose
attr_reader :item
end
def klass_for(name)
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
183

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@sandimetz Apr 2014
item is a role
184

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@sandimetz Apr 2014
GildedRose
tick
Normal
tick
Brie
tick
Sulfuras
attr_reader :item
tick
Backstage
attr_reader
:quality,
:days_remaining
185

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@sandimetz Apr 2014
attr_reader :item
GildedRose
ItemRole
def tick
def quality
def days_remaining
186

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@sandimetz Apr 2014
attr_reader :item
ItemRole
def tick
def quality
def days_remaining
GildedRose
187

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@sandimetz Apr 2014
attr_reader :item
def tick
end
def quality
end
def days_remaining
end
ItemRole
def tick
def quality
def days_remaining
GildedRose
187

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@sandimetz Apr 2014
attr_reader :item
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
GildedRose
ItemRole
def tick
def quality
def days_remaining
188

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@sandimetz Apr 2014
Foo
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
attr_reader :item
GildedRose
ItemRole
def tick
def quality
def days_remaining
189

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@sandimetz Apr 2014
Foo
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
attr_reader :item
attr_reader :rose
GildedRose
ItemRole
def tick
def quality
def days_remaining
189

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@sandimetz Apr 2014
Foo
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
attr_reader :item
attr_reader :rose
def doit
rose.tick
rose.quality
rose.days_remaining
end
GildedRose
ItemRole
def tick
def quality
def days_remaining
189

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@sandimetz Apr 2014
Foo
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
attr_reader :item
attr_reader :rose
def doit
rose.tick
rose.quality
rose.days_remaining
end
GildedRose
ItemRole
def tick
def quality
def days_remaining
190

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@sandimetz Apr 2014
Foo
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
attr_reader :item
attr_reader :rose
def doit
rose.tick
rose.quality
rose.days_remaining
end
GildedRose
ItemRole
def tick
def quality
def days_remaining
Middleman
190

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@sandimetz Apr 2014
Foo
attr_reader :item
attr_reader :rose
GildedRose
ItemRole
def tick
def quality
def days_remaining
191

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@sandimetz Apr 2014
Foo
attr_reader :item
attr_reader :rose
def getit
@rose =
GildedRose.new(
‘normal’, ...)
end
GildedRose
ItemRole
def tick
def quality
def days_remaining
191

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@sandimetz Apr 2014
Foo
def initialize(name,...)
@item =
klass_for(name).
new(
quality,
days_remaining)
end
def klass_for(name)
case name
when 'normal'
Normal
attr_reader :item
attr_reader :rose
def getit
@rose =
GildedRose.new(
‘normal’, ...)
end
GildedRose
ItemRole
def tick
def quality
def days_remaining
191

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@sandimetz Apr 2014
Foo
def initialize(name,...)
@item =
klass_for(name).
new(
quality,
days_remaining)
end
def klass_for(name)
case name
when 'normal'
Normal
attr_reader :item
attr_reader :rose
def getit
@rose =
GildedRose.new(
‘normal’, ...)
end
GildedRose
ItemRole
def tick
def quality
def days_remaining
Item
Factory
191

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@sandimetz Apr 2014
class GildedRose
attr_reader :item
end
def klass_for(name)
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
192

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@sandimetz Apr 2014
module GildedRose
attr_reader :item
end
def klass_for(name)
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
193

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@sandimetz Apr 2014
module GildedRose
attr_reader :item
def self.for(name, quality, days_remaining)
end
def klass_for(name)
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
194

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@sandimetz Apr 2014
module GildedRose
attr_reader :item
end
def self.klass_for(name)
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
195

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@sandimetz Apr 2014
module GildedRose
attr_reader :item
klass_for(name).new(quality, days_remaining)
end
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
196

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@sandimetz Apr 2014
module GildedRose
end
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
197

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@sandimetz Apr 2014
module GildedRose
end
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
198

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@sandimetz Apr 2014
module GildedRose
end
# ...
end
def tick
item.tick
end
def quality
item.quality
end
def days_remaining
item.days_remaining
end
class Normal
class Brie
class Sulfuras
class Backstage
end
Middleman
198

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@sandimetz Apr 2014
module GildedRose
end
# ...
end
class Normal
class Brie
class Sulfuras
class Backstage
end
199

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@sandimetz Apr 2014
Foo
def self.for(name,...)
end
attr_reader :rose
def getit
@rose =
GildedRose.for(
‘normal’, ...)
end
GildedRose
200

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@sandimetz Apr 2014
Foo
attr_reader :rose
def getit
@rose =
GildedRose.for(
‘normal’, ...)
end
ItemRole
def tick
def quality
def days_remaining
def self.for(name,...)
end
GildedRose
201

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@sandimetz Apr 2014
extract common code
202

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@sandimetz Apr 2014
module GildedRose
end
# ...
end
class Normal
class Brie
class Sulfuras
class Backstage
end
203

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@sandimetz Apr 2014
module GildedRose
class Normal
end
def tick
# ...
end
end
204

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@sandimetz Apr 2014
module GildedRose
class Normal
end
def tick
# ...
end
end
class Brie
end
def tick
# ...
end
end
205

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@sandimetz Apr 2014
module GildedRose
class Normal
end
def tick
# ...
end
end
class Brie
end
def tick
206

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@sandimetz Apr 2014
module GildedRose
class Item
end
class Normal
end
def tick
# ...
end
end
class Brie
end
def tick
207

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal
def tick
# ...
end
end
class Brie
end
def tick
208

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie
end
def tick
209

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie
end
def tick
# ...
end
end
210

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie < Item
end
def tick
# ...
end
end
211

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie < Item
def tick
# ...
end
end
212

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie < Item
def tick
# ...
end
end
class Sulfuras < Item
def tick
end
end
class Backstage < Item
def tick
213

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@sandimetz Apr 2014
inheritance is not evil
214

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@sandimetz Apr 2014
but we sometimes are
215

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie < Item
def tick
# ...
end
end
def tick
end
end
def tick
216

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie < Item
def tick
# ...
end
end
def tick
end
end
def tick
Item
quality
days_remaining
216

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie < Item
def tick
# ...
end
end
def tick
end
end
def tick
Item
quality
days_remaining
Normal
Brie
Sulfuras
Backstage
quality
days_remaining
tick
216

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@sandimetz Apr 2014
module GildedRose
class Item
end
end
class Normal < Item
def tick
# ...
end
end
class Brie < Item
def tick
# ...
end
end
def tick
end
end
217

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@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
# ...
end
end
class Brie < Item
def tick
# ...
end
end
def tick
end
end
218

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@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
def tick
end
end
219

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@sandimetz Apr 2014
module GildedRose
class Item
def tick
end
end
def tick
end
end
220

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@sandimetz Apr 2014
module GildedRose
class Item
def tick
end
end
def tick
end
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Sulfuras
Backstage
end
end
221

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@sandimetz Apr 2014
module GildedRose
class Item
def tick
end
end
def tick
end
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
222

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@sandimetz Apr 2014
module GildedRose
class Item
def tick
end
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
223

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@sandimetz Apr 2014
module GildedRose
class Item
def tick
end
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
224

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@sandimetz Apr 2014
module GildedRose
class Item
def tick
end
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
225

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@sandimetz Apr 2014
extract conﬁguration
226

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@sandimetz Apr 2014
module GildedRose
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
end
227

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@sandimetz Apr 2014
module GildedRose
DEFAULT_CLASS = Item
SPECIALIZED_CLASSES = {
'normal' => Normal,
'Aged Brie' => Brie,
'Backstage passes to a TAFKAL80ETC concert' => Backstage }
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
end
228

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@sandimetz Apr 2014
module GildedRose
'normal' => Normal,
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
end
229

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@sandimetz Apr 2014
module GildedRose
'normal' => Normal,
klass_for(name).
new(quality, days_remaining)
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
end
230

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@sandimetz Apr 2014
module GildedRose
'normal' => Normal,
(SPECIALIZED_CLASSES[name] || DEFAULT_CLASS).
end
case name
when 'normal'
Normal
when 'Aged Brie'
Brie
Item
Backstage
end
end
end
231

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@sandimetz Apr 2014
module GildedRose
'normal' => Normal,
end
end
232

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@sandimetz Apr 2014
small objects
233

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@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
(SPECIALIZED_CLASSES[name] || DEFAULT_CLASS).new(quality,
end
end
234

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@sandimetz Apr 2014
module GildedRose
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
235

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@sandimetz Apr 2014
module GildedRose
'normal' => Normal,
end
end module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
236

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@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
(SPECIALIZED_CLASSES[name] || DEFAULT_CLASS).new(quality, days_remainin
end
end small objects
237

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@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end small objects
class GildedRose
end
def tick
if @name != 'Aged Brie' && @name != 'Backstage passes to a TAFKAL80ETC
if @quality > 0
@quality -‐= 1
end
end
else
if @quality < 50
@quality += 1
if @quality < 50
@quality += 1
end
end
if @quality < 50
@quality += 1
end
end
end
end
end
end
if @quality > 0
@quality -‐= 1
end
end
else
end
else
if @quality < 50
@quality += 1
end
end
end
end
end
big conditional
238

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@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
small methods
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
small objects
239

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@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
(SPECIALIZED_CLASSES[name] || DEFAULT_CLASS).new(quality, days_remaining)
end
end
0
25
50
big conditional small methods small objects
tick/for normal brie backstage other
Total Complexity
40
50
240

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@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
33
40
50
Total Complexity
241

View Slide

@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
50
84
40
Total Complexity
242

View Slide

@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
0
45
90
50
84
40
Total Complexity
242

View Slide

@sandimetz Apr 2014
class GildedRose
end
def tick
case name
when 'normal'
normal_tick
when 'Aged Brie'
brie_tick
sulfuras_tick
backstage_tick
end
end
def normal_tick
@quality -‐= 1
end
def brie_tick
@quality += 1
end
def sulfuras_tick
end
def backstage_tick
@quality += 1
end
end
0
45
90
50
84
40 33
86
Total Complexity
242

View Slide

@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
big cond small meth small objs
33
Complexity
40
50
243

View Slide

@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
GildedRose small meth small objs
33
Complexity
40
50
244

View Slide

@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
GildedRose GildedRose(2) small objs
33
Complexity
40
50
245

View Slide

@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
GildedRose GildedRose(2) many objs
33
Complexity
40
50
246

View Slide

@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
GildedRose GildedRose(2) many objs Backstage
33
Complexity
40
50
12
247

View Slide

@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
GildedRose GildedRose(2) many objs Backstage average
33
Complexity
40
50
7
12
248

View Slide

@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
GildedRose Backstage
Complexity
50
12
249

View Slide

@sandimetz Apr 2014
module GildedRose
class Item
end
def tick
end
end
class Normal < Item
def tick
@quality -‐= 1
end
end
class Brie < Item
def tick
@quality += 1
end
end
def tick
@quality += 1
end
end
'normal' => Normal,
end
end
0
25
50
GildedRose Backstage
Complexity
50
12
75%
249

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@sandimetz Apr 2014
Task:
Implement Conjured
250

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@sandimetz Apr 2014
module GildedRose
251

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@sandimetz Apr 2014
module GildedRose
class Conjured < Item
def tick
@quality -‐= 2
end
end
252

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@sandimetz Apr 2014
module GildedRose
def tick
@quality -‐= 2
end
end
'normal' => Normal,
'Backstage passes to a TAFKAL80ETC concert' => Backstage}
253

View Slide

@sandimetz Apr 2014
module GildedRose
def tick
@quality -‐= 2
end
end
'normal' => Normal,
'Backstage passes to a TAFKAL80ETC concert' => Backstage,
'Conjured Mana Cake' => Conjured }
254

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@sandimetz Apr 2014
# Running:
...............................
255

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@sandimetz Apr 2014
Summary
256

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@sandimetz Apr 2014
prefer duplication
over the wrong abstraction
257

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@sandimetz Apr 2014
reach for open / closed
258

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@sandimetz Apr 2014
make small things
259

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@sandimetz Apr 2014
refactor through complexity
260

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@sandimetz Apr 2014
refactor to simplicity
261

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@sandimetz Apr 2014
love your code
262

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@sandimetz Apr 2014
Sandi Metz
@sandimetz Apr 2014
263

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@sandimetz Apr 2014
Sandi Metz
@sandimetz
@sandimetz Apr 2014
263

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@sandimetz Apr 2014
Sandi Metz
@sandimetz
@sandimetz Apr 2014
http://sandimetz.com
263

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http://poodr.com
Sandi Metz
@sandimetz
@sandimetz Apr 2014
264

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@sandimetz Apr 2014
@sandimetz Apr 2014
http://practicalrailsbook.com
265

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@sandimetz Apr 2014
London Course
http://kickstartacademy.io/courses/
practical-object-oriented-design
June 25-27
July 3-4
266

View Slide

all the little things (railsconf)

all the little things (railsconf)

Sandi Metz

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