[SUMMARY] Clean Code Chapter 3: Functions (Robert C. Martin)

Small!

• 2 to 6 lines long for each function to be transparently obvious.
• Only 1 indent => everything in blocks (if, try …) should be a function call! 
• Big functions are where classes hide => extract classes from functions! (A class is a group of functions that uses a common set a variable with 1 scope of responsibility)

Do One Thing

• Functions should do one thing; they should do it well; they should do it only. 
• Extract sub functions and classes until it’s not possible. 

The Stepdown Rule

• Most abstract function at the top
• Sub functions with a lower level of abstraction below it (It is possible in JS thanks to hoisting)

Switch Statements

• Use them only when necessary. 
• Do not repeat them => use Polymorphism  and  the Abstract Factory pattern

Use Descriptive Names

• A long descriptive name is better than a short enigmatic name.
• Don’t be afraid to spend time choosing a name.
• Hunting for a good name may result in a favorable restructuring of the code.

Function Arguments

• Best: 0 (niladic) 
• 2nd: 1 (monadic)  => function and argument should form a verb/noun pair.
• 3rd: 2 (dyadic)
• More than two should be avoided when possible

Reducing Arguments

• Don’t use flag arguments in a function => split the function in two 
• Use Objects: circle(x, y, radius) => circle(point, radius) 
• More args => harder to test 

Have No Side Effects

• Function should do one thing, but it also does other hidden things => bugs!

Command Query Separation (CQS) 

• Query => returns the state on an object, no modification 
• Command => modify the state, returns nothing

Exceptions over Error Codes

• Returning error from command = violation of CQS. 
• Error handling is one thing and functions should do one thing.

Don’t Repeat Yourself (DRY)

• Eliminate duplication to have only one source of truth and one place to change.

Conclusion

Like writing a book where functions are verbs and classes are nouns, you don’t have clean code right away. You start with code that works as a first draft and refactor it to have a clean expressive code - TDD helps with that.  

For more details and analyses, I highly recommend reading the book!

The summary of the previous chapters are available as posts :)

#cleancode #tdd #cleanarchitecture #developpeur #fullstack