Code Smells in Elixir - CODE BEAM EU 2023

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CODE SMELLS IN ELIXIR CODE BEAM EU 2023

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ELAINE NAOMI WATANABE twitter.com/elaine_nw speakerdeck.com/elainenaomi linkedin.com/in/elainenaomi B.Sc. in Computer Engineering M.Sc. in Computer Science Senior Software Engineer @ TheRealReal Yesterday 11°C Berlin Germany GMT+2 Last Saturday 23°C São Paulo Brazil GMT-3

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https://speakerdeck.com/elainenaomi

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CODE SMELLS

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Code smells are sub-optimal design choices that can degrade different aspects of code quality Yamashita, Aiko, and Steve Counsell. "Code smells as system-level indicators of maintainability: An empirical study." Journal of Systems and Software 86.10 (2013): 2639-2653.

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They are indicators of software design ﬂaws that could potentially affect maintenance Yamashita, Aiko, and Steve Counsell. "Code smells as system-level indicators of maintainability: An empirical study." Journal of Systems and Software 86.10 (2013): 2639-2653.

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Alternative Classes with Different Interfaces Loops Lazy Element Speculative Generality Temporary Field Message Chains Middle Man Insider Trading Large Class 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

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REFACTORING

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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.

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Small behavior-preserving transformations

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CATALOG OF REFACTORINGS 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 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 https://refactoring.com/catalog/ 2018

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Identify a code smell To ﬁx now? Apply refactoring Run tests Yes No Finish

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HISTORY 💾

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22 Code smells 72 Refactoring techniques 1999

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Mainly focused on object-oriented programming languages

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So, is it not an issue for functional programming languages?

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So, is it not an issue for functional programming languages?

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OOP + FP 2018 18+ years later 24 code smells 61 refactoring techniques

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Erlang/OTP Code Smells

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Elixir Code Smells

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Prof. Marco Tulio Valente Prof. Lucas Francisco da Matta Vegi Federal University of Minas Gerais (UFMG) Belo Horizonte, Minas Gerais, Brazil

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https://homepages.dcc.ufmg.br/~mtov/pub/2022-icpc-era.pdf

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Elixir Brasil: Code Smells, Refactoring and Elixir (in Portuguese) https://www.youtube.com/watch?v=3-1PCurON4Q https://speakerdeck.com/elainenaomi/elixir-brasil-2020-code-smells-refactoring-e-elixir One of my talks was part of the data sources analyzed in the grey literature review

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https://homepages.dcc.ufmg.br/~mtov/pub/2023-emse-code-smells-elixir.pdf

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The Elixir Community Contribution https://doi.org/10.1007/s10664-023-10343-6

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https://github.com/lucasvegi/Elixir-Code-Smells

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https://doi.org/10.1007/s10664-023-10343-6

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CODE SMELLS IN ELIXIR

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TRADITIONAL CODE SMELLS

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EXAMPLE #1 Duplicated Code

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defmodule ShoppingCart do def calculate_shipping(zip_code, subscription) do if (Enum.member?([3, 4], subscription.id)) do 0 else 10.0 * Location.calculate(zip_code) end end def apply_discount(total, subscription) do if (Enum.member?([3, 4], subscription.id)) do total * 0.9 else total end end end

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Rewriting with pattern matching…

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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

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Applying a refactoring…

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defmodule Subscription do defstruct [:id, :shipping_tax, :discount_rate] def available_subscriptions do [ %Subscription{id: 3, shipping_tax: 0.0, discount_rate: 0.95}, %Subscription{id: 4, shipping_tax: 0.0, discount_rate: 0.9} ] end end Encapsulating the rules, centralizing them in one single place

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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 Now, the subscription type is transparent for this module

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EXAMPLE #2 Long Parameter List

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defmodule User do def create_user( name, email, password, username, status, active?, admin? ) do # ... end end

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defmodule User do def create_user( name, email, password, username, status, active?, admin? ) do # ... end end

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Applying a refactoring…

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defmodule User do def create_user( name, email, password, username, status, active?, admin? ) do # ... end end

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defmodule User do def create_user(user) do # ... end end It can be a map %{}

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defmodule User do def create_user(%User{} = user) do # ... end end or a new struct :)

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defmodule User do def create_user(%User{} = user) do # ... end end new_user = %User{ name: "Elaine", email: "[email protected]", password: "123", username: "elainenaomi", status: 1, active?: true, admin?: false } User.create_user(new_user)

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ELIXIR-SPECIFIC CODE SMELLS

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EXAMPLE #1 Using exceptions for control-flow

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defmodule Report do def print_status(value) do if is_integer(value) do #... "Result..." else raise RuntimeError, message: "Invalid argument. It is not integer!" end end end

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defmodule Report do def print_status(value) do if is_integer(value) do #... "Result..." else raise RuntimeError, message: "Invalid argument. It is not integer!" end end end

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defmodule Client do # Client forced to use exceptions for control-flow. def status(arg) do try do value = Report.print_status(arg) "All good! #{value}." rescue e in RuntimeError -> reason = e.message "Uh oh! #{reason}." end end end

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Applying a refactoring…

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defmodule Report do def print_status(value) do if is_integer(value) do #... "Result..." else raise RuntimeError, message: "Invalid argument. It is not integer!" end end end

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defmodule Report do def print_status(value) do if is_integer(value) do #... {:ok, "Result..."} else {:error, "Invalid argument. It is not integer!" end end end Error Monad

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defmodule Client do # Client forced to use exceptions for control-flow. def status(arg) do case Report.print_status(arg) do {:ok, value} -> "All good! #{value}." {:error, reason} -> "Uh oh! #{reason}." end end end

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EXAMPLE #2 Complex Extractions in Clauses

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def drive(%User{name: name, age: age}) when age >= 18 do "#{name} can drive" end def drive(%User{name: name, age: age}) when age < 18 do "#{name} cannot drive" end Extracting values for further usage and pattern/guard checking

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Applying a refactoring…

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def drive(%User{age: age} = user) when age >= 18 do %User{name: name} = user "#{name} can drive" end def drive(%User{age: age} = user) when age < 18 do %User{name: name} = user "#{name} cannot drive" end Extracting only pattern/guard-related variables

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def drive(%User{age: age} = user) when age >= 18 do "#{user.name} can drive" end def drive(%User{age: age} = user) when age < 18 do "#{user.name} cannot drive" end Using dot notation for accessing struct properties

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Elixir 1.16 will contain the complete catalog of code smells in Elixir They will be called "anti-patterns"

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https://hexdocs.pm/elixir/main/what-anti-patterns.html

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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

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IN PROGRESS

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Catalog of Refactorings

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https://homepages.dcc.ufmg.br/~mtov/pub/2023-icsme-nier-elixir.pdf

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Elixir Community ++ Research with Elixir

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https://github.com/lucasvegi/Elixir-Refactorings

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WHAT'S NEXT?

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Tooling

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Not all code smells are detectable by automating tools

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hexdocs.pm/credo Improving

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Developer’s experience and system’s knowledge play an important role in the identiﬁcation of some smells. F. Palomba, G. Bavota, M. Di Penta, R. Oliveto and A. De Lucia, "Do They Really Smell Bad? A Study on Developers' Perception of Bad Code Smells," 2014 IEEE International Conference on Software Maintenance and Evolution, Victoria, BC, Canada, 2014, pp. 101-110, doi: 10.1109/ICSME.2014.32.

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A.I.? GH Copilot ChatGPT etc.

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Metrics?

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Cyclomatic complexity

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ABC Software Metric

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WRAPPING UP

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History Traditional and Elixir-speciﬁc code smells Impact of code smells over time Refactoring techniques

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Code smells != Bugs

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Code smells → Potential design ﬂaws

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It's about the impact on the software maintenance and evolvability

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Understability and changeability matter

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Understability and changeability matter If you'd like to scale your team

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Understability and changeability matter If you wish to take time off :)

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Research indicates that almost 60% of programmers’ time is spent understanding code, rather than writing code. From The Programmer's Brain - Felienne Hermans

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Automated tests + Refactoring =

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https://martinfowler.com/bliki/TestCoverage.html

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https://martinfowler.com/articles/practical-test-pyramid.html

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To keep in mind: you don't need to ﬁx ALL code smells

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Prefer duplication over the wrong abstraction Sandi Metz https://sandimetz.com/blog/2016/1/20/the-wrong-abstraction

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Refactoring != Revolution

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It's all about accumulative improvements

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https://martinfowler.com/bliki/DesignStaminaHypothesis.html design payoff line no design good design cumulative functionality time

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Developer productivity Product evolvability Quality of end-product Self-improvement etc "Do developers care about code smells? An exploratory survey" A. Yamashita and L. Moonen, 2013 doi: 10.1109/WCRE.2013.6671299.

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Legacy code in Elixir

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How is your codebase in Elixir?

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Is it EASY TO CHANGE?

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speakerdeck.com/elainenaomi elainenaomi.dev Muito obrigada illustrations from undraw.co translation: thank you so much! Don't forget to check and participate in the discussions about the catalog of refactorings