style-guide.md

Scala Style Guide

IntelliJ settings

Automatic

The easiest way to comply with the style guide is to load the IntelliJ code_style.xml. You can load the xml file using the Manage ... button on the Editor > Code Style page. After loading it, select it from the drop-down list.

Manual

Our style differs slightly from the IntelliJ Scala plugin defaults. Make the following changes:

• Turn off Preferences > Editor > Code Style > Syntax > Other > Enforce procedure syntax for methods with Unit return type.

• Turn on Preferences > Editor > Code Style > Scala > Spaces > Other > Insert whitespaces in simple one line blocks.

• Turn off Preferences > Editor > Code Style > Scala > Wrapping and Braces > Align when multiline in all categories.

Guide

• Prefer

  def foo() { ... }

  to

  def foo(): Unit = { ... }

  In IntelliJ, turn off Preferences > Editor > Code Style > Syntax > Other > Enforce procedure syntax for methods with Unit return type.

• Prefix mutable data structures with mutable. That is, prefer

  import scala.collection.mutable
  ... mutable.ArrayBuilder[Byte] ...

  to

  import scala.collection.mutable.ArrayBuilder
  ... ArrayBuilder[Byte] ...

• Prefer None to Option.empty. Prefer Some(_) to Option(_) when the argument will never be null.

• Use require, assert and ensure liberally to check preconditions, conditions and post-conditions. Define a validate member to check object invariants and call where suitable.

• In IntelliJ, turn on Preferences > Editor > Code Style > Scala > Spaces > Other > Insert whitespaces in simple one line blocks.

• In IntelliJ, turn off Preferences > Editor > Code Style > Scala > Wrapping and Braces > Align when multiline in all categories. This helps the code from migrating too far to the right.