Scala Style Guide

27 Jul 2012 > Vikas Hazrati > vikas@knoldus.com > @vhazrati

Indentation

2 spaces Line wrapping

Indentation

Methods with several arguments

Naming convention

Camel case

Class KnoldusKnowledgeSession

Object – same like class

Methods, Variables, values, Annotations

def myFairMethod = ...

Parentheses for methods

foo1 can be accessed with or without parenthesesfoo2 cannot be accessed with parentheses

Accessors do not define parenthesesCall site should follow the declaration conventionNo parentheses, when the method has no side effect

Symbolic method names

! :: => Avoid

Symbolic method names should be reserved for

1. DSL2. Logically mathematical operations (e.g. a + b

or c :: d)3. Purely functional operations like joining

Monads (>>=)

Type Parameters

Single

More than one

Brevity

def add(a: Int, b: Int) = a + b Bad in java

Good in scalaReadableFew local fields involvedConcise code

Void Methods

Functions

Space between argument and return type

Nested Blocks

def foo = {

}

Should define brace on line of declaration

Splitting parentheses have a space

Classes

Single line

Four spaces

Two spaces

Ordering in a class

New line between declarations

Fields before use inmethods

def foo(bar: Baz): Bin = expr

def foo(bar: Baz) { // return type is Unit

expr

}

Functional Values

val f1 = { (a: Int, b: Int) => a + b }

val f2 = (a: Int, b: Int) => a + b

val f3 = (_: Int) + (_: Int)

val f4: (Int, Int) => Int = { _ + _ }

Control Structures

Comprehensions

Trivial Conditions

val res = if (foo) bar else baz

Files

Single logical compilation unit

Inbox.scala

Multiple files

Cohesive group

All multi-unit files should be given camelCase names with a lower-case first letter.

Help in identification

ScalaDoc

It is important to provide documentation for all packages, classes, traits, methods, and other

members.

ScalaDoc

Avoid!Method Returns → returns <what>This class does XXX - > Does <what>

Links to Scala lib classes as [[scala.option]]@return

Document what method 'does not' and 'should not' do

first sentence should be a summary of what the method does.Subsequent sentences explain in further detail

Packages

Overview of mainclasses

Examples of how to Use class

Classes, Objects & Traits