The DRY Principle has had a dramatic impact on the software development industry, however most software developers associate the DRY Principle with code duplication rather than duplicate knowledge. In this talk we explore why the DRY Principle is related to domain driven design and how you can identify premature abstractions in your codebase.

1. THE DRY PRINCIPLE
IS MISUNDERSTOOD

2. Steven Solomon
Lead Software Engineer
Twitter: @ssolo112
Medium: @ssolomon
LinkedIn: tinyurl.com/ssolo112

3. I’m writing a book.
It is a software
book with a story
leanpub.com/agilesoftware
Available Now!

4. DRY
PRINCIPLE

5. “DRYING UP CODE”

6. By Annie Spratt on Unsplash
GROCERY APPLICATION

7. Dry Goods
Produce Meats
WHAT IS IN THE APPLICATION?

8. Dry Goods
Produce Meats
Margin: 300%
Margin: 200%
Margin: 100%
PRICING GROCERIES

9. # produce.rb
class Produce
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal('100'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
PRODUCE

10. # dry_good.rb
class DryGood
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal(‘200'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
DRY GOOD

11. # meat.rb
class Meat
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal(‘300'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
MEAT

12. “DRY Principle is about removing
duplicate code
-Grocery App Developers

13. By Annie Spratt on Unsplash
GROCERY APPLICATION

14. class Meat
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal('300'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
class Produce
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal('100'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
class DryGood
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal('200'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
REMOVING CODE DUPLICATION

15. class Meat
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal('300'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
class Produce
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal('100'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
class DryGood
def initialize(cost)
@cost = cost
end
def price
psychological_price(@cost * BigDecimal('200'))
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
REMOVING CODE DUPLICATION

16. # priceable.rb
module Priceable
def price
psychological_price(@cost * @margin)
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

17. # priceable.rb
module Priceable
def price
psychological_price(@cost * @margin)
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

18. # produce.rb
class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
end
# meat.rb
class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
end
# dry_good.rb
class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
end

19. # produce.rb
class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
end
# meat.rb
class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
end
# dry_good.rb
class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
end

20. Djim Loic on Unsplash

21. 0
2.5
5
7.5
10
Iteration 1 Iteration 2 Iteration 3 Iteration 4
Bugs Stories
BUGS INCREASED OVER TIME

22. Ricardo Viana on Unsplash

23. # priceable.rb
module Priceable
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

24. WHY DID THIS HAPPEN?

25. THE DRY PRINCIPLE
IS NOT ABOUT
DUPLICATE CODE

26. “Every piece of knowledge must have a
single, unambiguous, authoritative
representation within a system
-Dave Thomas & Andy Hunt

27. TECHNIQUES

28. TALKING TO
THE
PRODUCT
TEAM

29. CROSS-FUNCTIONAL TEAM
Product Design
Software

30. CROSS-FUNCTIONAL TEAM LANGUAGES
Business User
Technical

31. DOMAIN LANGUAGE
Business User
Technical
Domain Language

32. Mark Rabe - Unsplash

33. Meat
Produce
Priceable
:price
DryGood

34. Meat
Produce
Priceable
:price
DryGood
???

35. Meat
Produce
Priceable
:price
DryGood

36. Meat
Produce
Priceable
:price
DryGood

37. Meat
Produce
:price DryGood
:price
:price

38. Business
User
Technical
DOMAIN LANGUAGE

39. Business
User
Technical
DryGood
Produce
Meat
DOMAIN LANGUAGE
Priceable

40. Business
User
Technical
DryGood
Produce
Meat
Priceable
DOMAIN LANGUAGE

41. Business
User
Technical
DryGood
Produce
Meat
DOMAIN LANGUAGE

42. Business
User
Technical
DryGood
Produce
Meat
DOMAIN LANGUAGE

43. TALKING TO
THE
PRODUCT
TEAM

44. BITS
VS
CLUMPS
https://www.facebook.com/notes/kent-
beck/bits-clumps-and-just-right/
792597974106402

45. DryGood Produce
CAN I REASON ABOUT THESE SEPARATELY?
:price:price

46. BACKLOG
➤ Produce prices are based on season
➤ Meat prices are based on cut
➤ Produce prices are based on region
➤ Fish prices are based on rarity
➤ Produce prices end in “34”

47. BACKLOG
➤ Produce prices are based on season
➤ Meat prices are based on cut
➤ Produce prices are based on region
➤ Fish prices are based on rarity
➤ Produce prices end in “34”

48. DryGood Produce
CAN I REASON ABOUT THESE SEPARATELY?
:price:price
Yes

49. ARE THEY SEPARATE?
Produce
Priceable
:price
DryGood

50. ARE THEY SEPARATE?
Produce
Priceable
:price
DryGood
No

51. ARE THEY SEPARATE?
Produce
Priceable
:price
DryGood

52. ARE THEY SEPARATE?
Produce
Priceable
:price
DryGood
Priceable
:price

53. ARE THEY SEPARATE?
Produce
:price
DryGood
:price

54. BITS
VS
CLUMPS
https://www.facebook.com/notes/kent-
beck/bits-clumps-and-just-right/
792597974106402

55. NOTICING
DIVERGENT
CHANGE

56. SHOTGUN SURGERY

57. # produce.rb
class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = 100.0
end
end
# meat.rb
class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = 300.0
end
end
# dry_good.rb
class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = 200.0
end
end
SHOTGUN SURGERY

58. # produce.rb
class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = 100.0
end
end
# meat.rb
class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = 300.0
end
end
# dry_good.rb
class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = 200.0
end
end
SHOTGUN SURGERY

59. # produce.rb
class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
end
# meat.rb
class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
end
# dry_good.rb
class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
end
SHOTGUN SURGERY

60. # produce.rb
class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
end
# meat.rb
class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
end
# dry_good.rb
class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
end
SHOTGUN SURGERY

61. DIVERGENT CHANGE

62. # priceable.rb
module Priceable
def price
psychological_price(@cost * @margin)
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
DIVERGENT CHANGE

63. # priceable.rb
module Priceable
def price
psychological_price(@cost * @margin)
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
DIVERGENT CHANGE
Steak prices are based on cut

64. # priceable.rb
module Priceable
def price
total += psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
DIVERGENT CHANGE
Steak prices are based on cut

65. # priceable.rb
module Priceable
def price
total += psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
DIVERGENT CHANGE

66. # priceable.rb
module Priceable
def price
total += psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
DIVERGENT CHANGE
Produce prices are based on season

67. # priceable.rb
module Priceable
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
DIVERGENT CHANGE
Produce prices are based on season

68. # priceable.rb
module Priceable
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
DIVERGENT CHANGE

69. Too
m
uch
duplication
N
ot
enough
separation

70. Too
m
uch
duplication
N
ot
enough
separation
Shotgun
Surgery
Divergent
Change

71. NOTICING
DIVERGENT
CHANGE

72. TECHNIQUES

73. GETTING
BACK TO
SAFETY

74. class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
end

75. class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
end

76. class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
end

77. class Produce
include Priceable
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
end

78. class Produce
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
def price(season = nil)
total = psychological_price(@price * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

79. class Produce
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

80. class Produce
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

81. class Produce
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

82. class Produce
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

83. class Produce
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
season != @growing_season ? total + 1 : total
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

84. class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
end

85. class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
end

86. class DryGood
include Priceable
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
end

87. class DryGood
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
def price(season = nil)
total = psychological_price(@price * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

88. class DryGood
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

89. class DryGood
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

90. class DryGood
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

91. class DryGood
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
def price()
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

92. class DryGood
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
def price()
psychological_price(@cost * @margin)
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

93. class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
end

94. class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
end

95. class Meat
include Priceable
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
end

96. class Meat
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
def price(season = nil)
total = psychological_price(@price * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

97. class Meat
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

98. class Meat
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

99. class Meat
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

100. class Meat
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
def price()
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

101. class Meat
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
def price()
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

102. module Priceable
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

104. module Priceable
def price(season = nil)
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
season != @growing_season ? total + 1 : total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

105. class Meat
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
def price()
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
class Produce
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if season != @growing_season
total + 1
else
total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
class DryGood
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
def price()
psychological_price(@cost * @margin)
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

106. “So what is the correct abstraction?
- You (Maybe)

107. class Meat
def initialize(cost, type, cut)
@cost = cost
@type = type
@cut = cut
@margin = BigDecimal('300')
end
def price()
total = psychological_price(@cost * @margin)
if @type == :steak && @cut == :flatiron
total + BigDecimal('5')
else
total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
class Produce
def initialize(cost, growing_season)
@cost = cost
@growing_season = growing_season
@margin = BigDecimal('100')
end
def price(season = nil)
total = psychological_price(@cost * @margin)
if season != @growing_season
total + 1
else
total
end
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end
class DryGood
def initialize(cost)
@cost = cost
@margin = BigDecimal('200')
end
def price()
psychological_price(@cost * @margin)
end
private
def psychological_price(amount)
if amount.ceil == amount
(amount + BigDecimal('0.50')).ceil - BigDecimal('0.01')
else
(amount).ceil - BigDecimal('0.01')
end
end
end

108. BACKLOG
➤ Produce prices are based on season
➤ Meat prices are based on cut
➤ Produce prices are based on region
➤ Fish prices are based on rarity
➤ Produce prices end in “34”

109. BACKLOG
➤ Produce prices are based on season
➤ Meat prices are based on cut
➤ Produce prices are based on region
➤ Fish prices are based on rarity
➤ Produce prices end in “34”

110. SUMMARY

111. ➤ DRY Principle is about duplicate knowledge
➤ Techniques to identify pre-mature abstractions
➤ Talk to product team
➤ Bits vs clumps
➤ Noticing Divergent Change
➤ Remove pre-mature abstractions
WHAT WE TALKED ABOUT

112. THANKS

113. QUESTIONS
Steven Solomon
Lead Software Engineer
Twitter: @ssolo112
Medium: @ssolomon
LinkedIn: tinyurl.com/ssolo112
leanpub.com/agilesoftware