Scala Best Practices by Loïc Knuchel

(meaning their are my personal ones, not community ones)

I believe there is 3 very different groups in the Scala community:

• OOP puristes: coming from OOP languages and use Scala as a better OOP language
• FP minimalists: sold to FP but want to keep code
• FP purists:

Codes used in this guide:

• [MUST] is for rules that should be transgressed only in last resort and needs an explanation of why in comment next to it
• [PREFER] is for rules that should be followed in most cases but can be sometimes transgressed for more practical code
• Rules in bold are the important ones I consider you essential to any Scala code

Table of contents

1. Preface
   • [MUST] Do not take theses rules as is, you should understand and adapt them to your context
2. General
   • [PREFER] Code comments should explain WHY the code has been done this way, not HOW it does it
   • [MUST] Names should be meaningful
3. Language
4. FP
   • [MUST] Functions should be total
   • [PREFER] Functions should be pure
5. Architecture
   • [MUST] Split technical and business code
   • [MUST] Encode business rules in types as much as possible
   • [MUST] Avoid building invalid objects
   • [MUST] Avoid temporal coupling
6. Performance
   • [MUST] Performance should not be discussed without a benchmark highlighting the problem and the metrics that must be reached
7. Play framework
8. Syntax
   • [PREFER] Functions should have less than 20 lines, less than 10 is better, more than 50 is not acceptable
   • [PREFER] Lines should be less than 120 chars, more than 160 is not acceptable
   • [PREFER] Indentation should use 2 spaces
   • [PREFER] Each file should be terminated by an empty line

Interesting tools

• scalafmt
• scalastyle
• wartRemover

References and inspirations

• Alexandru Nedelcu best practices
• Nicolas Rinaudo best practices
• Li Haoyi's Strategic Scala Style: Principle of Least Power Conciseness & Names Practical Type Safety Designing Datatypes
• Jakub Kozłowski talk: 7* sins of a Scala beginner (vidéo)
• Nicolas Rinaudo talk: Scala Best Practices I Wish Someone'd Told Me About (vidéo)
• Knoldus best practices
• Databricks best practices
• PayPal best practices
• Twitter best practices

Contribute

Open a PR or an Issue and let's discuss