Exploring Code Smells - ElixirConf US 2023

Code smells are indicators of potential design problems in software code. They can impact maintainability, readability, and overall code quality.

While code smells have been extensively studied in object-oriented programming languages, their applicability and identification in functional programming languages like Elixir remain a fascinating area of exploration.

In this talk, we will dive into the world of Elixir and uncover code smells that may arise in its codebase. We will explore the traditional code smells (including the newly cataloged Elixir-specific code smells), discuss their impact on Elixir applications, and provide practical insights into refactoring techniques to eliminate them.

Transcript

1. ElixirConf US 2023 EXPLORING CODE SMELLS
2. ELAINE NAOMI WATANABE B.Sc. in Computer Engineering M.Sc. in Computer Science Senior Software Engineer @ TheRealReal twitter.com/elaine_nw speakerdeck.com/elainenaomi linkedin.com/in/elainenaomi
4. The RealReal - Elixir Adoption Story youtube.com/watch?v=sTs_4T1ufLY
5. CODE SMELLS
7. https://ieeexplore.ieee.org/document/6671299 2013
8. https://ieeexplore.ieee.org/document/6671299 2013
9. Do Developers Care about Code Smells? 2013
10. Do Developers Care about Code Smells? Concerns about code smells 2013
11. Do Developers Care about Code Smells? Concerns about code smells 2013
12. Do Developers Care about Code Smells? 52% Concerns about code smells 2013
13. What are their concerns about code smells?
14. Developer productivity Product evolvability Quality of end-product Self-improvement etc What are their concerns about code smells?
15. Do Developers Care about Code Smells? 52% Concerns about code smells 2013
16. Do Developers Care about Code Smells? Concerns about code smells 2013 26%
17. Lack of awareness about code smells No concerns
18. 2013 2013
19. Knowledge about code smells 2013 2013
20. Knowledge about code smells 2013 2013 58%
21. #
22. TERMINOLOGY
23. https://martinfowler.com/bliki/CodeSmell.html https://en.wikipedia.org/wiki/Code_smell CODE (BAD) SMELLS Any characteristic in the source code that may indicate a deeper quality problem in the system
24. ?
25. ? Nope
26. They are symptoms of poor design and implementation choice. Tufano, Michele et al. "When and why your code starts to smell bad". 37th IEEE International Conference on Software Engineering (2015): 403-414.
27. https://martinfowler.com/bliki/DesignStaminaHypothesis.html design payoff line no design good design cumulative functionality time
28. Code smells may slow down development or increase the risk of bugs or failures in the future https://en.wikipedia.org/wiki/Code_smell
29. 1999 22 code smells
30. 2018 18+ years later 24 code smells
31. Mysterious Name Duplicated Code Long Function Long Parameter List Global Data Mutable Data Divergent Change Shotgun Surgery Feature Envy Data Clumps Primitive Obsession Repeated Switches Loops Lazy Element Speculative Generality Temporary Field Message Chains Middle Man Insider Trading Large Class Alternative Classes with Different Interfaces Data Class Refused Bequest Comments 2018
32. And how to fix code smells?
33. 1999 22 code smells
34. 22 code smells 72 refactoring techniques 1999
35. 2018 18+ years later 24 code smells 61 refactoring techniques
36. 2018 18+ years later 24 code smells 61 refactoring techniques
37. CATALOG OF REFACTORINGS Change Function Declaration Change Reference to Value Change Value to Reference Collapse Hierarchy Combine Functions into Class Combine Functions into Transform Consolidate Conditional Expression Decompose Conditional Encapsulate Collection Encapsulate Record Encapsulate Variable Extract Class Extract Function Extract Superclass Extract Variable Hide Delegate Inline Class Inline Function Inline Variable Introduce Assertion Introduce Parameter Object Introduce Special Case Move Field Move Function Move Statements into Function Move Statements to Callers Parameterize Function Preserve Whole Object Pull Up Constructor Body Pull Up Field Pull Up Method Push Down Field Push Down Method Remove Dead Code Remove Flag Argument Remove Middle Man Remove Setting Method Remove Subclass Rename Field Rename Variable Replace Command with Function Replace Conditional with Polymorphism Replace Constructor with Factory Function Replace Derived Variable with Query Replace Function with Command Replace Inline Code with Function Call Replace Loop with Pipeline Replace Nested Conditional with Guard Clauses Replace Parameter with Query Replace Primitive with Object Replace Query with Parameter Replace Subclass with Delegate Replace Superclass with Delegate Replace Temp with Query Replace Type Code with Subclasses Separate Query from Modifier Slide Statements Split Loop Split Phase Split Variable Substitute Algorithm https://refactoring.com/catalog/ 2018
38. REFACTORING
45. CI is failing for weeks…
46. Hard to test, hard to deliver…
48. And, occasionally …
49. This is NOT refactoring
50. https://martinfowler.com/books/refactoring.html https://en.wikipedia.org/wiki/Code_refactoring REFACTORING A controlled technique for improving the design of an existing code base.
51. Small behavior-preserving transformations
52. Small behavior-preserving transformations *about the observable behavior
53. Identify a code smell To fix now? Apply Refactoring Run tests Yes Next No Finish
55. defmodule Cart do # ... def exec(i, d) do i |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(d) end end
56. defmodule Cart do # ... def exec(i, d) do i |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(d) end end What are these variables?
57. Code Smell: "Mysterious Name" Also called "Bad Naming"
58. Refactoring: "Rename Variable"
59. defmodule Cart do # ... def exec(i, d) do i |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(d) end end Rename the variables
60. defmodule Cart do # ... def exec(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end
61. defmodule Cart do # ... def exec(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end Run tests
62. defmodule Cart do # ... def exec(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end What does `exec` mean?
63. Code Smell: "Mysterious Name"
64. defmodule Cart do # ... def calculate_total(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end
65. Refactoring: "Change Function Declaration"
66. defmodule Cart do # ... def calculate_total(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end
67. defmodule Cart do # ... def calculate_total(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end Find all old references and update them
68. defmodule Cart do # ... def calculate_total(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end Run tests
69. defmodule Cart do # ... def calculate_total(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end
70. Code Smell: "Mysterious Name"
71. Refactoring: "Rename Field"
72. defmodule Cart do # ... def calculate_total(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end
73. defmodule Cart do # ... def calculate_total(items, cart_discount) do items |> Enum.map(& &1.pr * &1.qt) |> Enum.sum() |> Kernel.-(cart_discount) end end Skipping for now :)
74. #
75. What are we trying to achieve?
76. + Maintainability + Extensibility + Reusability + Code readability + Performance + Clarity What are we trying to achieve?
77. #
78. Finding code smells
80. defmodule WeatherAnalysis do def evaluate(temperature, unit) do if temperature > 30 and unit == "C" do "It's hot!" else if temperature <= 30 and temperature > 15 and unit == "C" do "It's not that hot nor that cold!" else if temperature <= 15 and unit == "C" do "It's cold." end end end end end Temperature-based analysis (Celsius only)
81. Temperature-based analysis (Celsius only) defmodule WeatherAnalysis do def evaluate(temperature, unit) do if temperature > 30 and unit == "C" do "It's hot!" else if temperature <= 30 and temperature > 15 and unit == "C" do "It's not that hot nor that cold!" else if temperature <= 15 and unit == "C" do "It's cold." end end end end end
82. defmodule WeatherAnalysis do def evaluate(temperature, unit) do if (temperature > 30 and unit == "C") or (temperature > 89.6 and unit == "F") do "It's hot!" else if (temperature <= 30 and temperature > 15 and unit == "C") or (temperature <= 89.6 and temperature > 59 and unit == "F") do "It's not that hot nor that cold!" else if (temperature <= 15 and unit == "C") or (temperature <= 59 and unit == "F") do "It's cold." end end end end end Temperature-based analysis (Celsius and Fahrenheit)
83. defmodule WeatherAnalysis do def evaluate(temperature, unit) do if (temperature > 30 and unit == "C") or (temperature > 89.6 and unit == "F") do "It's hot!" else if (temperature <= 30 and temperature > 15 and unit == "C") or (temperature <= 89.6 and temperature > 59 and unit == "F") do "It's not that hot nor that cold!" else if (temperature <= 15 and unit == "C") or (temperature <= 59 and unit == "F") do "It's cold." end end end end end Temperature-based analysis (Celsius and Fahrenheit)
84. Temperature-based analysis (Celsius and Fahrenheit) defmodule WeatherAnalysis do def evaluate(temperature, unit) do if (temperature > 30 and unit == "C") or (temperature > 89.6 and unit == "F") do "It's hot!" else if (temperature <= 30 and temperature > 15 and unit == "C") or (temperature <= 89.6 and temperature > 59 and unit == "F") do "It's not that hot nor that cold!" else if (temperature <= 15 and unit == "C") or (temperature <= 59 and unit == "F") do "It's cold." end end end end end
86. Let's use pattern matching!
87. defmodule WeatherAnalysis do def evaluate(temperature, "C") when temperature > 30, do: "It's hot!" def evaluate(temperature, "F") when temperature > 89.6, do: "It's hot!" def evaluate(temperature, "C") when temperature <= 30 and temperature > 15, do: "It's not that hot nor that cold!" def evaluate(temperature, "F") when temperature <= 89.6 and temperature > 59, do: "It's not that hot nor that cold!" def evaluate(temperature, "C") when temperature <= 15, do: "It's cold." def evaluate(temperature, "F") when temperature <= 59, do: "It's cold." end
88. defmodule WeatherAnalysis do def evaluate(temperature, "C") when temperature > 30, do: "It's hot!" def evaluate(temperature, "F") when temperature > 89.6, do: "It's hot!" def evaluate(temperature, "C") when temperature <= 30 and temperature > 15, do: "It's not that hot nor that cold!" def evaluate(temperature, "F") when temperature <= 89.6 and temperature > 59, do: "It's not that hot nor that cold!" def evaluate(temperature, "C") when temperature <= 15, do: "It's cold." def evaluate(temperature, "F") when temperature <= 59, do: "It's cold." end
90. In both examples: Duplicated code for Fahrenheit and Celsius Many execution paths
91. TRADITIONAL CODE SMELLS IN ELIXIR CONTEXT
92. Code Smell: "Duplicated Code"
93. Refactorings Extract Function, Slide Statements, Pull Up Method Code Smell Duplicated code
94. Refactorings Extract Function, Slide Statements, Pull Up Method DRY, Single Responsibility Principle Code Smell Duplicated code
95. #
96. defmodule WeatherAnalysis do def evaluate(temperature, "C") when temperature > 30, do: "It's hot!" def evaluate(temperature, "F") when temperature > 89.6, do: "It's hot!" def evaluate(temperature, "C") when temperature <= 30 and temperature > 15, do: "It's not that hot nor that cold!" def evaluate(temperature, "F") when temperature <= 89.6 and temperature > 59, do: "It's not that hot nor that cold!" def evaluate(temperature, "C") when temperature <= 15, do: "It's cold." def evaluate(temperature, "F") when temperature <= 59, do: "It's cold." end
97. Refactoring: Extract Function
98. defmodule WeatherAnalysis do def evaluate(temperature, "C") when temperature > 30, do: "It's hot!" def evaluate(temperature, "F") when temperature > 89.6, do: "It's hot!" def evaluate(temperature, "C") when temperature <= 30 and temperature > 15, do: "It's not that hot nor that cold!" def evaluate(temperature, "F") when temperature <= 89.6 and temperature > 59, do: "It's not that hot nor that cold!" def evaluate(temperature, "C") when temperature <= 15, do: "It's cold." def evaluate(temperature, "F") when temperature <= 59, do: "It's cold." end
99. defmodule WeatherAnalysis do def evaluate(temperature, unit) do temperature |> parse(unit) |> do_evaluate() end # ... end
100. defmodule WeatherAnalysis do def evaluate(temperature, unit) do temperature |> parse(unit) |> do_evaluate() end # ... end
101. defmodule WeatherAnalysis do # ... defp parse(temperature, "C"), do: temperature defp parse(temperature, "F"), do: (temperature - 32) * 5 / 9 # ... end
102. defmodule WeatherAnalysis do def evaluate(temperature, unit) do temperature |> parse(unit) |> do_evaluate() end # ... end
103. defmodule WeatherAnalysis do # ... defp do_evaluate(temperature) when temperature > 30, do: "It's really hot!" defp do_evaluate(temperature) when temperature <= 30 and temperature > 15, do: "It's not that hot nor that cold!" defp do_evaluate(temperature) when temperature <= 15, do: "It's cold." end
104. Code Smell: "Large Class" * Large Module
105. Refactorings Extract Class, Extra Superclass, Replace Type Code with Subclasses Code Smell Large Class
106. defmodule ShoppingCart do # Rule 1 def calculate_total(items, subscription) do # ... end # Rule 2 def calculate_shipping(zip_code, %{id: 3}), do: 0.0 def calculate_shipping(zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _) do 10.0 * Location.calculate(zip_code) end # Rule 3 def apply_discount(total, %{id: 3}), do: total * 0.9 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total # Rule 4 def send_message_subscription(%{id: 3}, _), do: nil def send_message_subscription(%{id: 4}, _), do: nil def send_message_subscription(subscription, user), do: Subscription.send_email_upgrade(subscription, user) # Rule 5 def print(user, order) do # ... end end
107. Rule #1 - Calculate Total defmodule ShoppingCart do # Rule 1 def calculate_total(items, subscription) do # ... end # Rule 2 def calculate_shipping(zip_code, %{id: 3}), do: 0.0 def calculate_shipping(zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _) do 10.0 * Location.calculate(zip_code) end # Rule 3 def apply_discount(total, %{id: 3}), do: total * 0.9 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total # Rule 4 def send_message_subscription(%{id: 3}, _), do: nil def send_message_subscription(%{id: 4}, _), do: nil def send_message_subscription(subscription, user), do: Subscription.send_email_upgrade(subscription, user) # Rule 5 def print(user, order) do # ... end end Rule #2 - Calculate Shipping Taxes Rule #3 - Apply Discount Rule #4 - Send Subscription Notification Rule #5 - Print Order
108. Hard to read Hard to explain what the module does Multiple business rules defmodule ShoppingCart do # Rule 1 def calculate_total(items, subscription) do # ... end # Rule 2 def calculate_shipping(zip_code, %{id: 3}), do: 0.0 def calculate_shipping(zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _) do 10.0 * Location.calculate(zip_code) end # Rule 3 def apply_discount(total, %{id: 3}), do: total * 0.9 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total # Rule 4 def send_message_subscription(%{id: 3}, _), do: nil def send_message_subscription(%{id: 4}, _), do: nil def send_message_subscription(subscription, user), do: Subscription.send_email_upgrade(subscription, user) # Rule 5 def print(user, order) do # ... end end
109. Refactoring: "Extract Class"
110. defmodule ShoppingCart do # Rule 1 def calculate_total(items, subscription) do # ... end # Rule 2 def calculate_shipping(zip_code, %{id: 3}), do: 0.0 def calculate_shipping(zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _) do 10.0 * Location.calculate(zip_code) end # Rule 3 def apply_discount(total, %{id: 3}), do: total * 0.9 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total # Rule 4 def send_message_subscription(%{id: 3}, _), do: nil def send_message_subscription(%{id: 4}, _), do: nil def send_message_subscription(subscription, user), do: Subscription.send_email_upgrade(subscription, user) # Rule 5 def print(user, order) do # ... end end
111. defmodule ShoppingCart do # Rule 1 def calculate_total(items, subscription) do # ... end # Rule 2 def calculate_shipping(zip_code, %{id: 3}), do: 0.0 def calculate_shipping(zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _) do 10.0 * Location.calculate(zip_code) end # Rule 3 def apply_discount(total, %{id: 3}), do: total * 0.9 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total # Rule 4 def send_message_subscription(%{id: 3}, _), do: nil def send_message_subscription(%{id: 4}, _), do: nil def send_message_subscription(subscription, user), do: Subscription.send_email_upgrade(subscription, user) # Rule 5 def print(user, order) do # ... end end defmodule UserNotification do def send_message_subscription(%{id: 3}, _), do: nil def send_message_subscription(%{id: 4}, _), do: nil def send_message_subscription(subscription, user) do Subscription.send_email_upgrade(subscription, user) end end Extract module
112. defmodule ShoppingCart do # Rule 1 def calculate_total(items, subscription) do # ... end # Rule 2 def calculate_shipping(zip_code, %{id: 3}), do: 0.0 def calculate_shipping(zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _) do 10.0 * Location.calculate(zip_code) end # Rule 3 def apply_discount(total, %{id: 3}), do: total * 0.9 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total # Rule 4 def send_message_subscription(%{id: 3}, _), do: nil def send_message_subscription(%{id: 4}, _), do: nil def send_message_subscription(subscription, user), do: Subscription.send_email_upgrade(subscription, user) # Rule 5 def print(user, order) do # ... end end Before: #5 Rules
113. defmodule ShoppingCart do # Rule 1 def calculate_total(items, subscription) do # ... end # Rule 2 def calculate_shipping(zip_code, %{id: 3}), do: 0.0 def calculate_shipping(zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _) do 10.0 * Location.calculate(zip_code) end # Rule 3 def apply_discount(total, %{id: 3}), do: total * 0.9 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total # Rule 5 def print(user, order) do # ... end end After: #4 Rules
114. Code Smell: "Long Function"
115. Refactorings Replace Temp with Query, Introduce Parameter Object, Preserve Whole Object, Split Loop, Replace Function with Command, Decompose Conditional, Replace Conditional with Polymorphism Code Smell Long Function
116. #
118. About cognition process in programming activities
119. #
120. Small change across several different files Code Smell: "Shotgun Surgery"
121. Refactorings Move Function, Move Field, Combine Functions into Class, Combine Functions into Transform, Split Phase, Inline Function, Inline Class Code Smell Shotgun Surgery
122. defmodule ShoppingCart do def calculate_shipping(_zip_code, %{id: 3}), do: 0.0 def calculate_shipping(_zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _), do: 10.0 * Location.calculate(zip_code) def apply_discount(total, %{id: 3}), do: total * 0.95 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total end
123. defmodule ShoppingCart do def calculate_shipping(_zip_code, %{id: 3}), do: 0.0 def calculate_shipping(_zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _), do: 10.0 * Location.calculate(zip_code) def apply_discount(total, %{id: 3}), do: total * 0.95 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total end Enum.member?([3, 4], subscription.id)
124. defmodule ShoppingCart do def calculate_shipping(_zip_code, %{id: 3}), do: 0.0 def calculate_shipping(_zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _), do: 10.0 * Location.calculate(zip_code) def apply_discount(total, %{id: 3}), do: total * 0.95 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total end Enum.member?([3, 4], subscription.id)
125. defmodule ShoppingCart do def calculate_shipping(_zip_code, %{id: 3}), do: 0.0 def calculate_shipping(_zip_code, %{id: 4}), do: 0.0 def calculate_shipping(zip_code, _), do: 10.0 * Location.calculate(zip_code) def apply_discount(total, %{id: 3}), do: total * 0.95 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, _), do: total end Enum.member?([3, 4], subscription.id)
126. defmodule ShoppingCart do def calculate_shipping(_zip_code, %{id: 3}), do: 0.0 def calculate_shipping(_zip_code, %{id: 4}), do: 0.0 def calculate_shipping(_zip_code, %{id: 8}), do: 0.0 def calculate_shipping(zip_code, _), do: 10.0 * Location.calculate(zip_code) def apply_discount(total, %{id: 3}), do: total * 0.95 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, %{id: 8}), do: total * 0.85 def apply_discount(total, _), do: total end Enum.member?([3, 4, 8], subscription.id)
127. defmodule SubscriptionRenewal do def execute(%{id: id}, user) do case id do 3 -> Billing.perform(user, id, 90.0) 4 -> Billing.perform(user, id, 95.0) 8 -> Billing.perform(user, id, 100.0) end end end Another small change after global search
128. defmodule SubscriptionRenewal do def execute(%{id: id}, user) do case id do 3 -> Billing.perform(user, id, 90.0) 4 -> Billing.perform(user, id, 95.0) 8 -> Billing.perform(user, id, 100.0) end end end Another small change after global search
129. Refactoring: "Move Field"
130. defmodule ShoppingCart do def calculate_shipping(_zip_code, %{id: 3}), do: 0.0 def calculate_shipping(_zip_code, %{id: 4}), do: 0.0 def calculate_shipping(_zip_code, %{id: 8}), do: 0.0 def calculate_shipping(zip_code, _), do: 10.0 * Location.calculate(zip_code) def apply_discount(total, %{id: 3}), do: total * 0.95 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, %{id: 8}), do: total * 0.85 def apply_discount(total, _), do: total end Enum.member?([3, 4, 8], subscription.id) Shipping Discount
131. defmodule SubscriptionRenewal do def execute(%{id: id}, user) do case id do 3 -> Billing.perform(user, id, 90.0) 4 -> Billing.perform(user, id, 95.0) 8 -> Billing.perform(user, id, 100.0) end end end Renewal
132. defmodule Subscription do defstruct [:id, :price, :shipping_tax, :discount_rate] def available_subscriptions do [ %Subscription{id: 3, price: 90.0, shipping_tax: 0.0, discount_rate: 0.95}, %Subscription{id: 4, price: 95.0, shipping_tax: 0.0, discount_rate: 0.9}, %Subscription{id: 8, price: 100.0, shipping_tax: 0.0, discount_rate: 0.85} ] end end
133. defmodule Subscription do defstruct [:id, :price, :shipping_tax, :discount_rate] def available_subscriptions do [ %Subscription{id: 3, price: 90.0, shipping_tax: 0.0, discount_rate: 0.95}, %Subscription{id: 4, price: 95.0, shipping_tax: 0.0, discount_rate: 0.9}, %Subscription{id: 8, price: 100.0, shipping_tax: 0.0, discount_rate: 0.85} ] end end
134. defmodule SubscriptionRenewal do def execute(%{id: id}, user) do case id do 3 -> Billing.perform(user, id, 90.0) 4 -> Billing.perform(user, id, 95.0) 8 -> Billing.perform(user, id, 100.0) end end end
135. defmodule SubscriptionRenewal do # ... def execute(subscription, user) do Billing.perform(user, subscription.id, subscription.price) end end
136. defmodule ShoppingCart do def calculate_shipping(_zip_code, %{id: 3}), do: 0.0 def calculate_shipping(_zip_code, %{id: 4}), do: 0.0 def calculate_shipping(_zip_code, %{id: 8}), do: 0.0 def calculate_shipping(zip_code, _), do: 10.0 * Location.calculate(zip_code) def apply_discount(total, %{id: 3}), do: total * 0.95 def apply_discount(total, %{id: 4}), do: total * 0.9 def apply_discount(total, %{id: 8}), do: total * 0.85 def apply_discount(total, _), do: total end Enum.member?([3, 4, 8], subscription.id)
137. defmodule ShoppingCart do # ... def calculate_shipping(_, %Subscription{shipping_tax: shipping_tax}), do: shipping_tax def calculate_shipping(zip_code, _), do: 10.0 * Location.calculate(zip_code) def apply_discount(total, %Subscription{discount_rate: discount_rate}), do: total * discount_rate def apply_discount(total, _), do: total end
138. #
139. These examples are for illustrative purposes Be mindful about issues when using float for monetary calculations (not only in Elixir!)
140. https://hexdocs.pm/elixir/1.15.5/Float.html
141. https://www.smbc-comics.com/?id=2999 0.1 + 0.2 == 0.3 0.1 + 0.2 == 0.30000000000000004 > false > true https://0.30000000000000004.com/ Unexpected loss of precision during rounding
142. #
143. Not all of the traditional code smells are applicable to Elixir context
144. Loops Lazy Element Speculative Generality Temporary Field Message Chains Middle Man Insider Trading Large Class Alternative Classes with Different Interfaces Data Class Refused Bequest Comments Mysterious Name Duplicated Code Long Function Long Parameter List Global Data Mutable Data Divergent Change Shotgun Surgery Feature Envy Data Clumps Primitive Obsession Repeated Switches 2018
145. https://doi.org/10.1007/s10664-023-10343-6
146. Prof. Marco Tulio Valente Prof. Lucas Francisco da Matta Vegi Federal University of Minas Gerais (UFMG) Belo Horizonte, Minas Gerais, Brazil
147. ELIXIR CODE SMELLS
148. About sub-optimal code structures that can harm the internal quality of Elixir systems
149. 14 Design-related smells 09 Low-level concerns smells
150. https://doi.org/10.1007/s10664-023-10343-6
151. https://github.com/lucasvegi/Elixir-Code-Smells
152. #
153. Design-related smells
154. Code Smell: "Unrelated multi-clause function"
155. Multi-clause functions in Elixir Multi-clause functions to group unrelated functionalities Code Smell Unrelated multi-clause function = Code smell != Code smell
157. def update(%User{} = user, new_email) when new_email != nil do %{user | email: new_email} end def update(%User{} = user, _new_email), do: user def update(%User.PaymentMethod{} = pay_method, default?) do %{pay_method | default: default?} end def update(%User.Notification{} = notification, channel) do %{notification | channel: channel} end
158. def update(%User{} = user, new_email) when new_email != nil do %{user | email: new_email} end def update(%User{} = user, _new_email), do: user def update(%User.PaymentMethod{} = pay_method, default?) do %{pay_method | default: default?} end def update(%User.Notification{} = notification, channel) do %{notification | channel: channel} end
159. def update(%User{} = user, new_email) when new_email != nil do %{user | email: new_email} end def update(%User{} = user, _new_email), do: user def update(%User.PaymentMethod{} = pay_method, default?) do %{pay_method | default: default?} end def update(%User.Notification{} = notification, channel) do %{notification | channel: channel} end #3 #2 #1
160. Refactoring
161. def update(%User{} = user, new_email) when new_email != nil do %{user | email: new_email} end def update(%User{} = user, _new_email), do: user def update(%User.PaymentMethod{} = pay_method, default?) do %{pay_method | default: default?} end def update(%User.Notification{} = notification, channel) do %{notification | channel: channel} end #1
162. @doc """ Updates a user's email address. """ def update_user_email(%User{} = user, new_email) when new_email != nil do %{user | email: new_email} end def update_user_email(%User{} = user, _new_email), do: user #1 New function
163. def update(%User{} = user, new_email) when new_email != nil do %{user | email: new_email} end def update(%User{} = user, _new_email), do: user def update(%User.PaymentMethod{} = pay_method, default?) do %{pay_method | default: default?} end def update(%User.Notification{} = notification, channel) do %{notification | channel: channel} end #2
164. @doc """ Updates user's default payment method. """ def update_user_payment_method(%User.PaymentMethod{} = pay_method, default?) do %{pay_method | default: default?} end #2 New function
165. def update(%User{} = user, new_email) when new_email != nil do %{user | email: new_email} end def update(%User{} = user, _new_email), do: user def update(%User.PaymentMethod{} = pay_method, default?) do %{pay_method | default: default?} end def update(%User.Notification{} = notification, channel) do %{notification | channel: channel} end #3
166. @doc """ Updates a user's notification preferences. """ def update_user_notification(%User.Notification{} = notification, channel) do %{notification | channel: channel} end #3 New function
167. Code Smell: "Compile-time global configuration"
168. Code Smell Compile-time global configuration Module attributes Defined at compile-time Application Environment May not be available in memory during compile-time/build-time *warnings or errors can be triggered by Elixir
169. defmodule DashSplitter do @parts Application.fetch_env!(:app_config, :parts) def split(string) when is_binary(string) do String.split(string, "-", parts: @parts) end end
170. defmodule DashSplitter do @parts Application.fetch_env!(:app_config, :parts) def split(string) when is_binary(string) do String.split(string, "-", parts: @parts) end end ** (ArgumentError) could not fetch application environment :parts for application :app_config because the application was not loaded nor configured
171. defmodule DashSplitter do @parts Application.compile_env(:app_config, :parts, 3) def split(string) when is_binary(string) do String.split(string, "-", parts: @parts) end end *with default
172. Compile time vs Runtime https://elixir-lang.org/getting-started/mix-otp/config-and-releases.html#configuration
173. #
174. Low-level concerns smells
175. Code Smell: "Complex else clauses in with"
176. `with` statement with a single complex `else` block Code Smell Complex else clauses in with = Code smell `with` statement + else != Code smell
177. def open_decoded_file(path) do with {:ok, encoded} <- File.read(path), {:ok, value} <- Base.decode64(encoded) do value else {:error, _} -> :badfile :error -> :badencoding end end Code Smell Complex else clauses in with
178. def open_decoded_file(path) do with {:ok, encoded} <- File.read(path), {:ok, value} <- Base.decode64(encoded) do value else {:error, _} -> :badfile :error -> :badencoding end end Code Smell Complex else clauses in with Difficult to know from which clause the error value came.
179. Refactoring
180. def open_decoded_file(path) do with {:ok, encoded} <- File.read(path), {:ok, value} <- Base.decode64(encoded) do value else {:error, _} -> :badfile :error -> :badencoding end end Code Smell Complex else clauses in with
181. Code Smell Complex else clauses in with def open_decoded_file(path) do with {:ok, encoded} <- file_read(path), {:ok, value} <- base_decode64(encoded) do value end end
182. Code Smell Complex else clauses in with def open_decoded_file(path) do with {:ok, encoded} <- file_read(path), {:ok, value} <- base_decode64(encoded) do value end end
183. defp file_read(path) do case File.read(path) do {:ok, contents} -> {:ok, contents} {:error, _} -> :badfile end end Code Smell Complex else clauses in with
184. defp file_read(path) do case File.read(path) do {:ok, contents} -> {:ok, contents} {:error, _} -> :badfile end end Code Smell Complex else clauses in with
185. Code Smell Complex else clauses in with def open_decoded_file(path) do with {:ok, encoded} <- file_read(path), {:ok, value} <- base_decode64(encoded) do value end end
186. Code Smell Complex else clauses in with defp base_decode64(contents) do case Base.decode64(contents) do {:ok, contents} -> {:ok, contents} :error -> :badencoding end end
187. Code Smell Complex else clauses in with defp base_decode64(contents) do case Base.decode64(contents) do {:ok, contents} -> {:ok, contents} :error -> :badencoding end end
188. Code Smell: "Dynamic Atom Creation"
189. Creating atoms dynamically with no control Code Smell Complex else clauses in with = Code smell Creating atoms dynamically != Code smell *Atoms are constants that are not garbage collected by the Erlang VM
190. defmodule Identifier do def generate(id) when is_bitstring(id) do String.to_atom(id) #<= dynamic atom creation!! end end
191. defmodule Identifier do def generate(id) when is_bitstring(id) do String.to_atom(id) #<= dynamic atom creation!! end end
192. Refactoring
193. defmodule Identifier do def generate(id) when is_bitstring(id) do String.to_atom(id) #<= dynamic atom creation!! end end
194. defmodule Identifier do def generate(id) when is_bitstring(id) do String.to_existing_atom(id) #<= maps a string to an existing atom! end end
195. Elixir 1.16
196. https://hexdocs.pm/elixir/main/what-anti-patterns.html
197. Code-related anti-patterns Design-related anti-patterns Process-related anti-patterns Meta-programming anti-patterns
198. Anti-pattern structure Name Unique, To facilitate communication Problem How it can harm code quality What impacts it can have for developers Example Code + textual description Refactoring Suggested changes to improve code quality
199. Anti-pattern structure Name Unique, To facilitate communication Problem How it can harm code quality What impacts it can have for developers Example Code + textual description Refactoring Suggested changes to improve code quality
201. WHAT'S NEXT?
202. #1 - Catalog of Refactorings for Elixir Code Smells
203. https://homepages.dcc.ufmg.br/~mtov/pub/2023-icsme-nier-elixir.pdf 2023
204. #2 - Tooling
205. hexdocs.pm/credo Improving
206. A.I.? GH Copilot ChatGPT etc.
207. #3 - Metrics?
208. Cyclomatic complexity
210. ABC Software Metric
212. WRAPPING UP
213. History Traditional and Elixir code smells Impact of code smells over time Refactoring techniques
214. # Understability and changeability matter
215. Research indicates that almost 60% of programmers’ time is spent understanding code, rather than writing code. From The Programmer's Brain - Felienne Hermans
216. # Automated tests + Refactoring =
217. https://martinfowler.com/bliki/TestCoverage.html
218. https://martinfowler.com/articles/practical-test-pyramid.html
219. # Refactoring != Revolution
220. It's all about accumulative improvements
221. #
222. Legacy code in Elixir
223. How is your Elixir codebase?
224. Is it EASY TO CHANGE?
225. speakerdeck.com/elainenaomi elainenaomi.dev Muito obrigada illustrations from undraw.co translation: thank you so much!
226. railsgirls.com.br
227. 2018 2020 2021 2019 2020 2018
230. CARNIVAL EDITION ELIXIR