You have probably heard of the DRY Principle, but what you don’t know is that it has nothing to do with duplicate code. In this talk I (Steven Solomon) will teach you to re-think the DRY Principle, how to identify incorrectly “DRY” code, and how to refactor your code so that it is easy to change again.

1. THE DRY PRINCIPLE
IS MISUNDERSTOOD

2. Steven Solomon
Senior Software Engineer
Twitter: @ssolo112
Medium: @ssolomon

3. DRY
PRINCIPLE

4. By Annie Spratt on Unsplash
GROCERY APPLICATION

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

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

7. # 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

8. # 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

9. # 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

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

11. By Annie Spratt on Unsplash
GROCERY APPLICATION

12. 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

13. 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

14. # 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

15. # 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

16. # 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

17. # 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

18. Djim Loic on Unsplash

19. Ricardo Viana on Unsplash

20. # 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

21. WHY DID THIS HAPPEN?

22. THE DRY PRINCIPLE
IS NOT ABOUT
DUPLICATE CODE

23. WHAT IS THE
DRY PRINCIPLE
REALLY ABOUT?

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

25. TECHNIQUES

26. TALKING TO
THE
PRODUCT
TEAM

27. BALANCED TEAM
Product Design
Software

28. BALANCED TEAM LANGUAGE
Business User
Technical
Balanced Language

29. BALANCED TEAM LANGUAGE
Business User
Technical
Balanced Language

30. Mark Rabe - Unsplash

31. Meat
Produce
Priceable
:price
DryGood

32. Meat
Produce
Priceable
:price
DryGood
???

33. Meat
Produce
Priceable
:price
DryGood

34. Meat
Produce
Priceable
:price
DryGood

35. Meat
Produce
:price DryGood
:price
:price

36. Business
User
Technical
BALANCED TEAM LANGUAGE

37. Business
User
Technical
DryGood
Produce
Meat
BALANCED TEAM LANGUAGE
Priceable

38. Business
User
Technical
DryGood
Produce
Meat
Priceable
BALANCED TEAM LANGUAGE

39. Business
User
Technical
DryGood
Produce
Meat
BALANCED TEAM LANGUAGE

40. Business
User
Technical
DryGood
Produce
Meat
BALANCED TEAM LANGUAGE

41. TALKING TO
THE
PRODUCT
TEAM

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

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

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

45. ARE THEY SEPARATE?
Produce
Priceable
:price
DryGood

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

47. ARE THEY SEPARATE?
Produce
Priceable
:price
DryGood

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

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

50. BITS
VS
CLUMPS

51. NOTICING
DIVERGENT
CHANGE

52. SHOTGUN SURGERY

53. # 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

54. # 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

55. # 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

56. # 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

57. DIVERGENT CHANGE

58. # 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

59. # 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

60. # 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

61. # 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

62. # 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

63. # 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

64. # 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

65. Too
m
uch
duplication
N
ot
enough
separation

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

67. NOTICING
DIVERGENT
CHANGE

68. GETTING
BACK TO
SAFETY

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

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

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

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

73. 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

74. 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

75. 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

76. 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

77. 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

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(@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

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 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

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 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

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

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

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

84. 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

85. 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

86. 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

87. 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

88. 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

89. 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

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

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

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

93. 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

94. 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

95. 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

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(@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

97. 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

98. 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

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
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(season = nil)
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

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

101. ➤ 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

102. THANKS

103. I’m writing a book.
It is a software
book with a story
leanpub.com/agilesoftware

104. QUESTIONS
Steven Solomon
Senior Software Engineer
Twitter: @ssolo112
Medium: @ssolomon
leanpub.com/agilesoftware