A talk explaining how to define `good code`. Using `Code Complete` as a reference to guide over the quality definition and introducing Linters (Credo) and Dialyzer (Dialyxir)

1. Qualidade
A Panacéia para seu código Elixir

2. Hello!
Weverton Timoteo
@wevtimoteo

3. ● Very useful item to up your RPG
character level
● I’d recommend to buy at least 5
● Drops from some medium level
mobs
Panacea

4. ● Was a goddess of universal remedy
● Panacea traditionally had a potion
with which she healed the sick
● A substance meant to cure all
diseases
● "Something used to solve all
problems"
Panacea (from Greek mythology)

5. “
Any fool can write code that a
computer can understand.
Good programmers write code that
humans can understand.
– Martin Fowler

6. How Do You Define
“Good Code” ?

7. maintainability?

8. Efficiency Modularity Elegance
What's the first thing that comes to your
mind?
Proper design
decision

9. You write readable code because it helps other
people to read your code“
Code Complete, Steve McConnel
Error rate
Comprehensibility
Reviewability
Debugging
Modifiability

10. Simplicity
is it about the number of lines?

11. Readability
comments, conventions, naming

12. Modularity
its all about reusability

13. Layering
attention to the boundaries of each layer

14. Design
plan before build

15. Efficiency
too many connections?

16. Elegance
solve problems with proper solutions

17. Clarity
do you really know what you have to do?

18. Balance

19. How to achieve
this?

20. ● Erlang Open Telecom Protocol
● it's not that much about telecom anymore
● libraries available with the virtual machine
● OTP compliant: basically following process architecture
OTP (Open Telecom Protocol)

21. BEAM
● Bogdan's Erlang Abstract Machine
○ emulator and loader were first implemented by Bogumil Hausman
● Björn's Erlang Abstract Machine
○ completely rewritten by Björn Gustavsson
● BEAM bytecode files have the .beam file extension

22. ● Static analysis tool that identifies software
discrepancies, such as:
○ definite type errors
○ code that has become dead
○ unreachable because of programming error
○ unnecessary tests
● Erlang modules or entire (sets of) applications
(.beam files)
DIscrepancy AnaLYZer for ERlang programs
DIALYZER

23. The Persistent Lookup Table (PLT)
● Stores the result of an analysis (acting like a cache)
● Then it can be used as starting point for later analyses
● .plt file extension

24. Gradual Typing
Best of Static and Dynamic Worlds:
● Some variables and functions can have type declaration
● Developer decides which ones makes sense to declare
● Tool or Compiler can still check correctness and consistency of
usage

25. ● It allows us to generate tests from the code
examples in a module/function/macro's
documentation
● Similar to Python's doctest
● Able to refer to specific numbered scenarios
● Copy-pasting examples from an actual IEx session
Doctests

26. ● Run Dialyzer (test environment) to see how the
types in API and the usage in the tests (calls)
Using Dialyzer for tests

27. Dialyzer (Cons)
● Output in Erlang format
● No indentation
● No formatting

28. Dialixyr
Mix tasks to simplify use of
Dialyzer in Elixir projects

29. Dialixyr - Explain

30. Dialixyr - Explain

31. Dialixyr - Explain

32. Dialixyr - Ignore file

33. is a tool that analyzes source code to flag
programming errors, bugs, stylistic errors,
and suspicious constructs
- Wikipedia
What is a linter?
“

34. Homoiconicity
● The code used to express a program is
written using the data structures of
that language
● The Lisp family languages (Common
Lisp, Scheme, Clojure, etc)
● Code is Data, Data is Code

35. Abstract Syntax Tree (AST)
● It tells us how expressions are represented
● Internal representation of our code
● Using quote/2 we can convert Elixir code into its
representation

36. AST: quote/2
Using quote/2 we can convert Elixir code into its representation

37. Is Elixir Homoiconic?
No!
If so:
● We would be writing in ASTs form
● It would bypass the lexing and parsing phase of Elixir compilation

38. ● Formats the given files and patterns
Code Formatting

39. ● Code Complexity (Cyclomatic Complexity, etc)
● Style and Pattern Checking
● Performance
● Unused code
● Reports
● Outdated packages
● Code without tests (no coverage)
● Magic number detector
What a Linter can do?

40. Dogma

41. Credo
● Also static analysis tool
● Checks
○ code consistency
○ readability
○ styleguides
○ conventions
● Useful for learning

42. mix credo categories

43. mix credo categories

44. Credo

45. And if all checks
succeed ?

46. Thanks!Let’s start analyzing
our code!
|> team
|> hiring()

47. References
● Code Complete: A Practical Handbook of Software Construction
● Elixir, processes and this thing called OTP
● Introducing HDD: Hughes Driven Development, com José Valim
● Credo
● Dialyzer
● Dialixyr
● Ebert: the code review assistant for your organization
● Metaprogramming in Elixir

48. More References
● ElixirConf 2016 - Dialyzer: Optimistic Type Checking for Erlang and Elixir
by Jason Voegele
● Gradualizer: A Gradual Type System for Erlang
● Learn You Some Erlang: OTP