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title: Clean Code Fundamentals subtitle: Functions ...

Pre-work

Timetable

Activity Time
Warmup 5 min
Exercise 1 20 min
Exercise 2 20 min
Exercise 3 20 min
Wrap up 5 min

Warmup

  • What are some "landmarks" you look for when you're reading code?
    • Type in the meeting chat

Exercise 1

  • Prompt
    • How to safely refactor code without breaking it? Discuss possible strategies.
    • What to do if code is not covered by tests?
  • Time limit: 10 minutes

Safe refactoring

  • Refactoring is a process of
    • restructuring existing code
    • without changing its external behavior
  • Safe refactoring
    • Put the system under a test
    • Run tests often
    • Understand test coverage to avoid blind spots

Common approach to working with legacy code

  • Create a "characterization test" that captures the current behavior
  • Restructure the code to enable testing of a specific part of the code
  • Write a test for wanted behavior that fails
  • Implement the behavior to make the test pass

Characterization test

  • This test has many names
    • "Characterization test"
    • "Golden Master"
    • "Snapshot test"
  • Characterization test checks general behavior
    • Uses fixed seed for program inputs
    • Checks that the output is the same as the previous run

Exercise 2

  • Prompt
    • What code behavior do you find suspicious and why?
    • What "code smells" do you find useful and why?
  • Time limit: 10 minutes

Code smells catalog

::: columns

:::: column

  • Bloaters
    • Long method
    • Long parameter list
    • Data clumps
    • Primitive obsession
    • Long class
  • Object-Orientation Abusers
    • Switch statements
    • Refused bequest
    • Alternative classes with different interfaces
    • Temporary field
  • Change Preventers
    • Divergent change
    • Shotgun surgery
    • Parallel inheritance hierarchies

::::

:::: column

  • Dispensables
    • Lazy class
    • Data class
    • Comments
    • Duplicate code
    • Dead code
    • Speculative generality
  • Couplers
    • Feature envy
    • Inappropriate intimacy
    • Incomplete library class
    • Message chains
    • Middle man

::::

:::

"Feature envy" code smell

  • Definition
    • A method accesses the data of another object more than its own data
  • Possible reason
    • After fields move to a data class/structure
  • Treatment
    • Move operations on data to the class as well

Exercise 3

  • Prompt
    • How to define if a function is doing "one thing"?
  • Time limit: 10 minutes

Where classes hide

  • Classes hide in long functions with many local variables
  • Functions that fill the screen are likely doing more than one thing
  • Functions crossing levels of abstraction

"Extract class" refactoring

  • Create characterizations test -- run often
  • Extract function body to a new class's invoke method
  • Extract local variables to fields
  • Extract methods or new classes
  • Repeat until you can't extract anymore

Wrap up

  • Functions should be small
  • Functions should do one thing
  • Functions should have one level of abstraction
  • Functions should have descriptive names

What is next?

  • Expect an e-mail with instructions for upcoming coding dojo

Final words

Always leave the code better than you found it.

-- The Software Craftsmanship Rule