ruby-style-guide

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A community-driven Ruby coding style guide

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= The Ruby Style Guide :idprefix: :idseparator: - :sectanchors: :sectlinks: :toc: preamble :toclevels: 1 ifndef::backend-pdf[] :toc-title: pass:[

] endif::[] :source-highlighter: rouge

== Introduction

[quote, Officer Alex J. Murphy / RoboCop]

Role models are important.

ifdef::env-github[] TIP: You can find a beautiful version of this guide with much improved navigation at https://rubystyle.guide. endif::[]

This Ruby style guide recommends best practices so that real-world Ruby programmers can write code that can be maintained by other real-world Ruby programmers. A style guide that reflects real-world usage gets used, while a style guide that holds to an ideal that has been rejected by the people it is supposed to help risks not getting used at all - no matter how good it is.

The guide is separated into several sections of related guidelines. We've tried to add the rationale behind the guidelines (if it's omitted we've assumed it's pretty obvious).

We didn't come up with all the guidelines out of nowhere - they are mostly based on the professional experience of the editors, feedback and suggestions from members of the Ruby community and various highly regarded Ruby programming resources, such as https://pragprog.com/book/ruby4/programming-ruby-1-9-2-0["Programming Ruby"] and http://www.amazon.com/Ruby-Programming-Language-David-Flanagan/dp/0596516177["The Ruby Programming Language"].

This style guide evolves over time as additional conventions are identified and past conventions are rendered obsolete by changes in Ruby itself.

ifdef::env-github[] You can generate a PDF copy of this guide using https://asciidoctor.org/docs/asciidoctor-pdf/[AsciiDoctor PDF], and an HTML copy https://asciidoctor.org/docs/convert-documents/#converting-a-document-to-html[with] https://asciidoctor.org/#installation[AsciiDoctor] using the following commands:

[TIP]

Install the

rouge
gem to get nice syntax highlighting in the generated document.

==== endif::[]

If you're into Rails or RSpec you might want to check out the complementary https://github.com/rubocop-hq/rails-style-guide[Ruby on Rails Style Guide] and https://github.com/rubocop-hq/rspec-style-guide[RSpec Style Guide].

TIP: https://github.com/rubocop-hq/rubocop[RuboCop] is a static code analyzer (linter) and formatter, based on this style guide.

=== Guiding Principles

[quote, Harold Abelson, Structure and Interpretation of Computer Programs]

Programs must be written for people to read, and only incidentally for machines to execute.

It's common knowledge that code is read much more often than it is written. The guidelines provided here are intended to improve the readability of code and make it consistent across the wide spectrum of Ruby code. They are also meant to reflect real-world usage of Ruby instead of a random ideal. When we had to choose between a very established practice and a subjectively better alternative we've opted to recommend the established practice.footnote:[Occasionally we might suggest to the reader to consider some alternatives, though.]

There are some areas in which there is no clear consensus in the Ruby community regarding a particular style (like string literal quoting, spacing inside hash literals, dot position in multi-line method chaining, etc.). In such scenarios all popular styles are acknowledged and it's up to you to pick one and apply it consistently.

Ruby had existed for over 15 years by the time the guide was created, and the language's flexibility and lack of common standards have contributed to the creations of numerous styles for just about everything. Rallying people around the cause of community standards took a lot of time and energy, and we still have a lot of ground to cover.

Ruby is famously optimized for programmer happiness. We'd like to believe that this guide is going to help you optimize for maximum programmer happiness.

[quote, Ralph Waldo Emerson]

A foolish consistency is the hobgoblin of little minds, adored by little statesmen and philosophers and divines.

A style guide is about consistency. Consistency with this style guide is important. Consistency within a project is more important. Consistency within one class or method is the most important.

However, know when to be inconsistent -- sometimes style guide recommendations just aren't applicable. When in doubt, use your best judgment. Look at other examples and decide what looks best. And don't hesitate to ask!

In particular: do not break backwards compatibility just to comply with this guide!

Some other good reasons to ignore a particular guideline:

• When applying the guideline would make the code less readable, even for someone who is used to reading code that follows this style guide.
• To be consistent with surrounding code that also breaks it (maybe for historic reasons) -- although this is also an opportunity to clean up someone else's mess (in true XP style).
• Because the code in question predates the introduction of the guideline and there is no other reason to be modifying that code.
• When the code needs to remain compatible with older versions of Ruby that don't support the feature recommended by the style guide.

=== Translations

Translations of the guide are available in the following languages:

NOTE: These translations are not maintained by our editor team, so their quality and level of completeness may vary. The translated versions of the guide often lag behind the upstream English version.

== Source Code Layout

[quote, Jerry Coffin (on indentation)]

Nearly everybody is convinced that every style but their own is ugly and unreadable. Leave out the "but their own" and they're probably right...

=== Source Encoding [[utf-8]]

Use

UTF-8
as the source file encoding.

TIP: UTF-8 has been the default source file encoding since Ruby 2.0.

=== Tabs or Spaces? [[tabs-or-spaces]]

Use only spaces for indentation. No hard tabs.

=== Indentation [[spaces-indentation]]

Use two spaces per indentation level (aka soft tabs).

[source,ruby]

def somemethod dosomething end

good

def somemethod dosomething

end

=== Maximum Line Length [[max-line-length]]

Limit lines to 80 characters.

TIP: Most editors and IDEs have configurations options to help you with that. They would typically highlight lines that exceed the length limit.

.Why Bother with 80 characters in a World of Modern Widescreen Displays?

A lot of people these days feel that a maximum line length of 80 characters is just a remnant of the past and makes little sense today. After all - modern displays can easily fit 200+ characters on a single line. Still, there are some important benefits to be gained from sticking to shorter lines of code.

First, and foremost - numerous studies have shown that humans read much faster vertically and very long lines of text impede the reading process. As noted earlier, one of the guiding principles of this style guide is to optimize the code we write for human consumption.

Additionally, limiting the required editor window width makes it possible to have several files open side-by-side, and works well when using code review tools that present the two versions in adjacent columns.

The default wrapping in most tools disrupts the visual structure of the code, making it more difficult to understand. The limits are chosen to avoid wrapping in editors with the window width set to 80, even if the tool places a marker glyph in the final column when wrapping lines. Some web based tools may not offer dynamic line wrapping at all.

Some teams strongly prefer a longer line length. For code maintained exclusively or primarily by a team that can reach agreement on this issue, it is okay to increase the line length limit up to 100 characters, or all the way up to 120 characters. Please, restrain the urge to go beyond 120 characters.

=== No Trailing Whitespace [[no-trailing-whitespace]]

Avoid trailing whitespace.

TIP: Most editors and IDEs have configuration options to visualize trailing whitespace and to remove it automatically on save.

=== Line Endings [[crlf]]

Use Unix-style line endings.footnote:[*BSD/Solaris/Linux/macOS users are covered by default, Windows users have to be extra careful.]

[TIP]

If you're using Git you might want to add the following configuration setting to protect your project from Windows line endings creeping in:

good - this catches only the exceptions of Errno::ENOENT class and its descendant classes

def foo readfile rescue Errno::ENOENT => e handleerror(e)

end

=== Using Exceptions for Flow of Control [[no-exceptional-flows]]

Don't use exceptions for flow of control.

[source,ruby]

begin n / d rescue ZeroDivisionError puts 'Cannot divide by 0!' end

good

if d.zero? puts 'Cannot divide by 0!' else n / d

end

=== Blind Rescues [[no-blind-rescues]]

Avoid rescuing the

Exception
class. This will trap signals and calls to
exit
, requiring you to
kill -9
the process.

[source,ruby]

begin # calls to exit and kill signals will be caught (except kill -9) exit rescue Exception puts "you didn't really want to exit, right?" # exception handling end

good

begin # a blind rescue rescues from StandardError, not Exception as many # programmers assume. rescue => e # exception handling end

also good

begin # an exception occurs here rescue StandardError => e # exception handling

end

=== Exception Rescuing Ordering [[exception-ordering]]

Put more specific exceptions higher up the rescue chain, otherwise they'll never be rescued from.

[source,ruby]

begin # some code rescue StandardError => e # some handling rescue IOError => e # some handling that will never be executed end

good

begin # some code rescue IOError => e # some handling rescue StandardError => e # some handling

end

=== Release External Resources [[release-resources]]

Release external resources obtained by your program in an

ensure
block.

[source,ruby]

f = File.open('testfile') begin # .. process rescue # .. handle error ensure f.close if f

end

=== Auto-release External Resources [[auto-release-resources]]

Use versions of resource obtaining methods that do automatic resource cleanup when possible.

bad - you need to close the file descriptor explicitly

f = File.open('testfile')

f.close

good - the file descriptor is closed automatically

File.open('testfile') do |f| # some action on the file

end

=== Standard Exceptions [[standard-exceptions]]

Prefer the use of exceptions from the standard library over introducing new exception classes.

== Assignment & Comparison

=== Parallel Assignment [[parallel-assignment]]

Avoid the use of parallel assignment for defining variables. Parallel assignment is allowed when it is the return of a method call, used with the splat operator, or when used to swap variable assignment. Parallel assignment is less readable than separate assignment.

[source,ruby]

a, b, c, d = 'foo', 'bar', 'baz', 'foobar'

good

a = 'foo' b = 'bar' c = 'baz' d = 'foobar'

swap the values that are assigned to each variable.

a = 'foo' b = 'bar'

a, b = b, a puts a # => 'bar' puts b # => 'foo'

good - method return

def multi_return [1, 2] end

first, second = multi_return

good - use with splat

first, *list = [1, 2, 3, 4] # first => 1, list => [2, 3, 4]

hello_array = *'Hello' # => ["Hello"]

a = *(1..3) # => [1, 2, 3]

=== Dealing with Trailing Underscore Variables in Destructuring Assignment [[trailing-underscore-variables]]

Avoid the use of unnecessary trailing underscore variables during parallel assignment. Named underscore variables are to be preferred over underscore variables because of the context that they provide. Trailing underscore variables are necessary when there is a splat variable defined on the left side of the assignment, and the splat variable is not an underscore.

[source,ruby]

foo = 'one,two,three,four,five'

Unnecessary assignment that does not provide useful information

first, second, _ = foo.split(',') first, , _ = foo.split(',') first, * = foo.split(',')

good

foo = 'one,two,three,four,five'

except for the last number of underscore elements

*beginning, _ = foo.split(',') *beginning, something, _ = foo.split(',')

a, = foo.split(',') a, b, = foo.split(',')

provides us with useful information.

first, _second = foo.split(',') first, _second, = foo.split(',')

first, *_ending = foo.split(',')

=== Self-assignment [[self-assignment]]

Use shorthand self assignment operators whenever applicable.

[source,ruby]

x = x + y x = x * y x = x**y x = x / y x = x || y x = x && y

good

x += y x = y x *= y x /= y x ||= y

x &&= y

=== Conditional Variable Initialization Shorthand [[double-pipe-for-uninit]]

Use

||=
to initialize variables only if they're not already initialized.

[source,ruby]

name = name ? name : 'Bozhidar'

name = 'Bozhidar' unless name

[WARNING]

Don't use

||=
to initialize boolean variables. (Consider what would happen if the current value happened to be
false
.)

enabled ||= true

good

enabled = true if enabled.nil?

====

=== Existence Check Shorthand [[double-amper-preprocess]]

Use

&&=
to preprocess variables that may or may not exist. Using
&&=
will change the value only if it exists, removing the need to check its existence with
if
.

[source,ruby]

if something something = something.downcase end

something = something ? something.downcase : nil

ok

something = something.downcase if something

good

something = something && something.downcase

better

something &&= something.downcase

=== Identity Comparison [[identity-comparison]]

Prefer

equal?
over
==
when comparing
object_id
.
Object#equal?
is provided to compare objects for identity, and in contrast
Object#==
is provided for the purpose of doing value comparison.

[source,ruby]

foo.objectid == bar.objectid

good

foo.equal?(bar)

Similarly, prefer using

Hash#compare_by_identity
than using
object_id
for keys:

[source,ruby]

hash = {} hash[foo.objectid] = :bar if hash.key?(baz.objectid) # ...

good

hash = {}.comparebyidentity hash[foo] = :bar

if hash.key?(baz) # ...

Note that

Set
also has
Set#compare_by_identity
available.

=== Explicit Use of the Case Equality Operator [[no-case-equality]]

Avoid explicit use of the case equality operator

===
. As its name implies it is meant to be used implicitly by
case
expressions and outside of them it yields some pretty confusing code.

[source,ruby]

Array === something (1..100) === 7 /something/ === some_string

good

something.is_a?(Array) (1..100).include?(7)

some_string.match?(/something/)

NOTE: With direct subclasses of

BasicObject
, using
is_a?
is not an option since
BasicObject
doesn't provide that method (it's defined in
Object
). In those rare cases it's OK to use
===
.

===

is_a?
vs
kind_of?
[[is-a-vs-kind-of]]

Prefer

is_a?
over
kind_of?
. The two methods are synonyms, but
is_a?
is the more commonly used name in the wild.

[source,ruby]

something.kind_of?(Array)

good

something.is_a?(Array)

===

is_a?
vs
instance_of?
[[is-a-vs-instance-of]]

Prefer

is_a?
over
instance_of?
.

While the two methods are similar,

is_a?
will consider the whole inheritance chain (superclasses and included modules), which is what you normally would want to do.
instance_of?
, on the other hand, only returns
true
if an object is an instance of that exact class you're checking for, not a subclass.

[source,ruby]

something.instance_of?(Array)

good

something.is_a?(Array)

===

==
vs
eql?
[[eql]]

Do not use

eql?
when using
==
will do. The stricter comparison semantics provided by
eql?
are rarely needed in practice.

bad - eql? is the same as == for strings

'ruby'.eql? some_str

good

'ruby' == some_str

1.0.eql? x # eql? makes sense here if want to differentiate between Integer and Float 1

== Blocks, Procs & Lambdas

=== Proc Application Shorthand [[single-action-blocks]]

Use the Proc invocation shorthand when the invoked method is the only operation of a block.

[source,ruby]

names.map { |name| name.upcase }

good

names.map(&:upcase)

=== Single-line Blocks Delimiters [[single-line-blocks]]

Prefer

{...}
over
do...end
for single-line blocks. Avoid using
{...}
for multi-line blocks (multi-line chaining is always ugly). Always use
do...end
for "control flow" and "method definitions" (e.g. in Rakefiles and certain DSLs). Avoid
do...end
when chaining.

[source,ruby]

names = %w[Bozhidar Filipp Sarah]

names.each do |name| puts name end

good

names.each { |name| puts name }

names.select do |name| name.start_with?('S') end.map { |name| name.upcase }

good

names.select { |name| name.start_with?('S') }.map(&:upcase)

Some will argue that multi-line chaining would look OK with the use of {...}, but they should ask themselves - is this code really readable and can the blocks' contents be extracted into nifty methods?

=== Explicit Block Argument [[block-argument]]

Consider using explicit block argument to avoid writing block literal that just passes its arguments to another block.

[source,ruby]

require 'tempfile'

def withtmpdir Dir.mktmpdir do |tmpdir| Dir.chdir(tmpdir) { |dir| yield dir } # block just passes arguments end end

good

def withtmpdir(&block) Dir.mktmpdir do |tmpdir| Dir.chdir(tmpdir, &block) end end

withtmpdir do |dir| puts "dir is accessible as a parameter and pwd is set: #{dir}"

end

=== Trailing Comma in Block Parameters [[no-trailing-parameters-comma]]

Avoid comma after the last parameter in a block, except in cases where only a single argument is present and its removal would affect functionality (for instance, array destructuring).

[source,ruby]

[[1, 2, 3], [4, 5, 6]].each do |a, b, c,| a + b + c end

good

[[1, 2, 3], [4, 5, 6]].each do |a, b, c| a + b + c end

[[1, 2, 3], [4, 5, 6]].each { |a, b, c,| a + b + c }

good

[[1, 2, 3], [4, 5, 6]].each { |a, b, c| a + b + c }

good - this comma is meaningful for array destructuring

[[1, 2, 3], [4, 5, 6]].map { |a,| a }

=== Nested Method Definitions [[no-nested-methods]]

Do not use nested method definitions, use lambda instead. Nested method definitions actually produce methods in the same scope (e.g. class) as the outer method. Furthermore, the "nested method" will be redefined every time the method containing its definition is invoked.

[source,ruby]

def foo(x) def bar(y) # body omitted end

bar(x) end

good - the same as the previous, but no bar redefinition on every foo call

def bar(y) # body omitted end

def foo(x) bar(x) end

also good

def foo(x) bar = ->(y) { ... } bar.call(x)

end

=== Multi-line Lambda Definition [[lambda-multi-line]]

Use the new lambda literal syntax for single-line body blocks. Use the

lambda
method for multi-line blocks.

[source,ruby]

l = lambda { |a, b| a + b } l.call(1, 2)

correct, but looks extremely awkward

l = ->(a, b) do tmp = a * 7 tmp * b / 50 end

good

l = ->(a, b) { a + b } l.call(1, 2)

l = lambda do |a, b| tmp = a * 7 tmp * b / 50

end

=== Stabby Lambda Definition with Parameters [[stabby-lambda-with-args]]

Don't omit the parameter parentheses when defining a stabby lambda with parameters.

[source,ruby]

l = ->x, y { something(x, y) }

good

l = ->(x, y) { something(x, y) }

=== Stabby Lambda Definition without Parameters [[stabby-lambda-no-args]]

Omit the parameter parentheses when defining a stabby lambda with no parameters.

[source,ruby]

l = ->() { something }

good

l = -> { something }

===

proc
vs
Proc.new
[[proc]]

Prefer

proc
over
Proc.new
.

[source,ruby]

p = Proc.new { |n| puts n }

good

p = proc { |n| puts n }

=== Proc Invocation [[proc-call]]

Prefer

proc.call()
over
proc[]
or
proc.()
for both lambdas and procs.

bad - looks similar to Enumeration access

l = ->(v) { puts v } l[1]

good - most compact form, but might be confusing for newcomers to Ruby

l = ->(v) { puts v } l.(1)

good - a bit verbose, but crystal clear

l = ->(v) { puts v }

l.call(1)

== Methods

=== Short Methods [[short-methods]]

Avoid methods longer than 10 LOC (lines of code). Ideally, most methods will be shorter than 5 LOC. Empty lines do not contribute to the relevant LOC.

=== No Single-line Methods [[no-single-line-methods]]

Avoid single-line methods. Although they are somewhat popular in the wild, there are a few peculiarities about their definition syntax that make their use undesirable. At any rate - there should be no more than one expression in a single-line method.

[source,ruby]

def toomuch; something; somethingelse; end

okish - notice that the first ; is required

def nobracesmethod; body end

okish - notice that the second ; is optional

def nobracesmethod; body; end

okish - valid syntax, but no ; makes it kind of hard to read

def some_method() body end

good

def some_method body

end

One exception to the rule are empty-body methods.

good

def no_op; end

=== Double Colons [[double-colons]]

Use

::
only to reference constants (this includes classes and modules) and constructors (like
Array()
or
Nokogiri::HTML()
). Do not use
::
for regular method invocation.

[source,ruby]

SomeClass::somemethod someobject::some_method

good

SomeClass.somemethod someobject.somemethod SomeModule::SomeClass::SOMECONST

SomeModule::SomeClass()

=== Colon Method Definition [[colon-method-definition]]

Do not use

::
to define class methods.

[source,ruby]

class Foo def self::some_method end end

good

class Foo def self.some_method end

end

=== Method Definition Parentheses [[method-parens]]

Use

def
with parentheses when there are parameters. Omit the parentheses when the method doesn't accept any parameters.

[source,ruby]

def some_method() # body omitted end

good

def some_method # body omitted end

def somemethodwith_parameters param1, param2 # body omitted end

good

def somemethodwith_parameters(param1, param2) # body omitted

end

=== Method Invocation Parentheses [[method-invocation-parens]]

Use parentheses around the arguments of method invocations, especially if the first argument begins with an open parenthesis

(
, as in
f((3 + 2) + 1)
.

x = Math.sin y

x = Math.sin(y)

array.delete e

good

array.delete(e)

temperance = Person.new 'Temperance', 30

good

temperance = Person.new('Temperance', 30)

==== Method Calls with No Arguments [[method-invocation-parens-no-args]]

Always omit parentheses for method calls with no arguments.

[source,ruby]

Kernel.exit!() 2.even?() fork() 'test'.upcase()

good

Kernel.exit! 2.even? fork

'test'.upcase

==== Methods That are Part of an Internal DSL [[method-invocation-parens-internal-dsl]]

Always omit parentheses for methods that are part of an internal DSL (e.g., Rake, Rails, RSpec):

[source,ruby]

validates(:name, presence: true)

good

validates :name, presence: true

==== Methods That Have "keyword" Status in Ruby [[method-invocation-parens-keyword]]

Always omit parentheses for methods that have "keyword" status in Ruby.

NOTE: Unfortunately, it's not exactly clear which methods have "keyword" status. There is agreement that declarative methods have "keyword" status. However, there's less agreement on which non-declarative methods, if any, have "keyword" status.

===== Declarative Methods That Have "keyword" Status in Ruby [[method-invocation-parens-declarative-keyword]]

Always omit parentheses for declarative methods (a.k.a. DSL methods or macro methods) that have "keyword" status in Ruby (e.g., various

Module
instance methods):

# body omitted

end

===== Non-Declarative Methods That Have "keyword" Status in Ruby [[method-invocation-parens-non-declarative-keyword]]

For non-declarative methods with "keyword" status (e.g., various

Kernel
instance methods), two styles are considered acceptable. By far the most popular style is to omit parentheses. Rationale: The code reads better, and method calls look more like keywords. A less-popular style, but still acceptable, is to include parentheses. Rationale: The methods have ordinary semantics, so why treat them differently, and it's easier to achieve a uniform style by not worrying about which methods have "keyword" status. Whichever one you pick, apply it consistently.

good (most popular)

puts temperance.age system 'ls' exit 1

also good (less popular)

puts(temperance.age) system('ls')

exit(1)

==== Using

super
with Arguments [[super-with-args]]

Always use parentheses when calling

super
with arguments:

super name, age

good

super(name, age)

IMPORTANT: When calling

super
without arguments,
super
and
super()
mean different things. Decide what is appropriate for your usage.

=== Too Many Params [[too-many-params]]

Avoid parameter lists longer than three or four parameters.

=== Optional Arguments [[optional-arguments]]

Define optional arguments at the end of the list of arguments. Ruby has some unexpected results when calling methods that have optional arguments at the front of the list.

[source,ruby]

def some_method(a = 1, b = 2, c, d) puts "#{a}, #{b}, #{c}, #{d}" end

somemethod('w', 'x') # => '1, 2, w, x' somemethod('w', 'x', 'y') # => 'w, 2, x, y' some_method('w', 'x', 'y', 'z') # => 'w, x, y, z'

good

def some_method(c, d, a = 1, b = 2) puts "#{a}, #{b}, #{c}, #{d}" end

somemethod('w', 'x') # => '1, 2, w, x' somemethod('w', 'x', 'y') # => 'y, 2, w, x'

some_method('w', 'x', 'y', 'z') # => 'y, z, w, x'

=== Boolean Keyword Arguments [[boolean-keyword-arguments]]

Use keyword arguments when passing boolean argument to a method.

[source,ruby]

def some_method(bar = false) puts bar end

bad - common hack before keyword args were introduced

def some_method(options = {}) bar = options.fetch(:bar, false) puts bar end

good

def some_method(bar: false) puts bar end

some_method # => false

some_method(bar: true) # => true

=== Keyword Arguments vs Optional Arguments [[keyword-arguments-vs-optional-arguments]]

Prefer keyword arguments over optional arguments.

[source,ruby]

def some_method(a, b = 5, c = 1) # body omitted end

good

def some_method(a, b: 5, c: 1) # body omitted

end

=== Keyword Arguments vs Option Hashes [[keyword-arguments-vs-option-hashes]]

Use keyword arguments instead of option hashes.

[source,ruby]

def some_method(options = {}) bar = options.fetch(:bar, false) puts bar end

good

def some_method(bar: false) puts bar

end

=== Private Global Methods [[private-global-methods]]

If you really need "global" methods, add them to Kernel and make them private.

== Classes & Modules

=== Consistent Classes [[consistent-classes]]

Use a consistent structure in your class definitions.

[source,ruby]

class Person # extend and include go first extend SomeModule include AnotherModule

# inner classes CustomError = Class.new(StandardError)

# constants are next SOME_CONSTANT = 20

# afterwards we have attribute macros attr_reader :name

# followed by other macros (if any) validates :name

# public class methods are next in line def self.some_method end

# initialization goes between class methods and other instance methods def initialize end

# followed by other public instance methods def some_method end

# protected and private methods are grouped near the end protected

def someprotectedmethod end

private

def someprivatemethod end

end

=== Mixin Grouping [[mixin-grouping]]

Split multiple mixins into separate statements.

[source,ruby]

class Person include Foo, Bar end

good

class Person # multiple mixins go in separate statements include Foo include Bar

end

=== Single-line Classes [[single-line-classes]]

Prefer a two-line format for class definitions with no body. It is easiest to read, understand, and modify.

[source,ruby]

FooError = Class.new(StandardError)

okish

class FooError < StandardError; end

ok

class FooError < StandardError

end

NOTE: Many editors/tools will fail to understand properly the usage of

Class.new
. Someone trying to locate the class definition might try a grep "class FooError". A final difference is that the name of your class is not available to the
inherited
callback of the base class with the
Class.new
form. In general it's better to stick to the basic two-line style.

=== File Classes [[file-classes]]

Don't nest multi-line classes within classes. Try to have such nested classes each in their own file in a folder named like the containing class.

foo.rb

class Foo class Bar # 30 methods inside end

class Car # 20 methods inside end

# 30 methods inside end

foo.rb

class Foo # 30 methods inside end

foo/bar.rb

class Foo class Bar # 30 methods inside end end

foo/car.rb

class Foo class Car # 20 methods inside end

end

=== Namespace Definition [[namespace-definition]]

Define (and reopen) namespaced classes and modules using explicit nesting. Using the scope resolution operator can lead to surprising constant lookups due to Ruby's https://cirw.in/blog/constant-lookup.html[lexical scoping], which depends on the module nesting at the point of definition.

[source,ruby]

module Utilities class Queue end end

class Utilities::Store Module.nesting # => [Utilities::Store]

def initialize # Refers to the top level ::Queue class because Utilities isn't in the # current nesting chain. @queue = Queue.new end end

good

module Utilities class WaitingList Module.nesting # => [Utilities::WaitingList, Utilities]

def initialize
@queue = Queue.new # Refers to Utilities::Queue
end


end

end

=== Modules vs Classes [[modules-vs-classes]]

Prefer modules to classes with only class methods. Classes should be used only when it makes sense to create instances out of them.

[source,ruby]

class SomeClass def self.some_method # body omitted end

def self.someothermethod # body omitted end end

good

module SomeModule module_function

def some_method # body omitted end

def someothermethod # body omitted end

end

===

module_function
[[module-function]]

Prefer the use of

module_function
over
extend self
when you want to turn a module's instance methods into class methods.

[source,ruby]

module Utilities extend self

def parse_something(string) # do stuff here end

def otherutilitymethod(number, string) # do some more stuff end end

good

module Utilities module_function

def parse_something(string) # do stuff here end

def otherutilitymethod(number, string) # do some more stuff end

end

=== Liskov [[liskov]]

When designing class hierarchies make sure that they conform to the https://en.wikipedia.org/wiki/Liskovsubstitutionprinciple[Liskov Substitution Principle].

=== SOLID design [[solid-design]]

Try to make your classes as https://en.wikipedia.org/wiki/SOLID[SOLID] as possible.

=== Define

to_s
[[define-to-s]]

Always supply a proper

to_s
method for classes that represent domain objects.

[source,ruby]

def initialize(firstname, lastname) @firstname = firstname @lastname = lastname end

def tos "#{firstname} #{last_name}" end

end

===

attr
Family [[attr_family]]

Use the

attr
family of functions to define trivial accessors or mutators.

[source,ruby]

class Person def initialize(firstname, lastname) @firstname = firstname @lastname = lastname end

def firstname @firstname end

def lastname @lastname end end

good

def initialize(firstname, lastname) @firstname = firstname @lastname = lastname end

end

=== Accessor/Mutator Method Names [[accessormutatormethod_names]]

For accessors and mutators, avoid prefixing method names with

get_
and
set_
. It is a Ruby convention to use attribute names for accessors (readers) and
attr_name=
for mutators (writers).

[source,ruby]

class Person def getname "#{@firstname} #{@last_name}" end

def setname(name) @firstname, @last_name = name.split(' ') end end

good

class Person def name "#{@firstname} #{@lastname}" end

def name=(name) @firstname, @lastname = name.split(' ') end

end

===

attr
[[attr]]

Avoid the use of

attr
. Use
attr_reader
and
attr_accessor

bad - creates a single attribute accessor (deprecated in Ruby 1.9)

attr :something, true attr :one, :two, :three # behaves as attr_reader

good

attr_accessor :something

===

Struct.new
[[struct-new]]

Consider using

Struct.new
, which defines the trivial accessors, constructor and comparison operators for you.

good

class Person attraccessor :firstname, :last_name

def initialize(firstname, lastname) @firstname = firstname @lastname = lastname end end

better

Person = Struct.new(:firstname, :lastname) do

end

=== No Extend

Struct.new
[[no-extend-struct-new]]

Don't extend an instance initialized by

Struct.new
. Extending it introduces a superfluous class level and may also introduce weird errors if the file is required multiple times.

[source,ruby]

class Person < Struct.new(:firstname, :lastname) end

good

Person = Struct.new(:firstname, :lastname)

=== Duck Typing [[duck-typing]]

Prefer https://en.wikipedia.org/wiki/Duck_typing[duck-typing] over inheritance.

[source,ruby]

class Animal # abstract method def speak end end

extend superclass

class Duck < Animal def speak puts 'Quack! Quack' end end

extend superclass

class Dog < Animal def speak puts 'Bau! Bau!' end end

good

class Duck def speak puts 'Quack! Quack' end end

class Dog def speak puts 'Bau! Bau!' end

end

=== No Class Vars [[no-class-vars]]

Avoid the usage of class (

@@
) variables due to their "nasty" behavior in inheritance.

[source,ruby]

class Parent @@class_var = 'parent'

def self.printclassvar puts @@class_var end end

class Child < Parent @@class_var = 'child' end

Parent.printclassvar # => will print 'child'

As you can see all the classes in a class hierarchy actually share one class variable. Class instance variables should usually be preferred over class variables.

=== Leverage Access Modifiers (e.g.

private
and
protected
) [[visibility]]

Assign proper visibility levels to methods (

private
,
protected
) in accordance with their intended usage. Don't go off leaving everything
public
(which is the default). After all we're coding in Ruby now, not in Python.

=== Access Modifiers Indentation [[indent-public-private-protected]]

Indent the

public
,
protected
, and
private
methods as much as the method definitions they apply to. Leave one blank line above the visibility modifier and one blank line below in order to emphasize that it applies to all methods below it.

good

class SomeClass def public_method # some code end

private

def private_method # some code end

def anotherprivatemethod # some code end

end

=== Defining Class Methods [[def-self-class-methods]]

Use

def self.method
to define class methods. This makes the code easier to refactor since the class name is not repeated.

[source,ruby]

class TestClass # bad def TestClass.some_method # body omitted end

# good def self.someothermethod # body omitted end

# Also possible and convenient when you # have to define many class methods. class << self def first_method # body omitted end

def second_method_etc
# body omitted
end


end

end

=== Alias Method Lexically [[alias-method-lexically]]

Prefer

alias
when aliasing methods in lexical class scope as the resolution of
self
in this context is also lexical, and it communicates clearly to the user that the indirection of your alias will not be altered at runtime or by any subclass unless made explicit.

[source,ruby]

class Westerner def first_name @names.first end

alias givenname firstname

end

Since

alias
, like
def
, is a keyword, prefer bareword arguments over symbols or strings. In other words, do
alias foo bar
, not
alias :foo :bar
.

Also be aware of how Ruby handles aliases and inheritance: an alias references the method that was resolved at the time the alias was defined; it is not dispatched dynamically.

[source,ruby]

class Fugitive < Westerner def first_name 'Nobody' end

end

In this example,

Fugitive#given_name
would still call the original
Westerner#first_name
method, not
Fugitive#first_name
. To override the behavior of
Fugitive#given_name
as well, you'd have to redefine it in the derived class.

[source,ruby]

class Fugitive < Westerner def first_name 'Nobody' end

alias givenname firstname

end

===

alias_method
[[alias-method]]

Always use

alias_method
when aliasing methods of modules, classes, or singleton classes at runtime, as the lexical scope of
alias
leads to unpredictability in these cases.

[source,ruby]

module Mononymous def self.included(other) other.classeval { aliasmethod :fullname, :givenname } end end

class Sting < Westerner include Mononymous

end

=== Class and

self
[[class-and-self]]

When class (or module) methods call other such methods, omit the use of a leading

self
or own name followed by a
.
when calling other such methods. This is often seen in "service classes" or other similar concepts where a class is treated as though it were a function. This convention tends to reduce repetitive boilerplate in such classes.

[source,ruby]

class TestClass # bad -- more work when class renamed/method moved def self.call(param1, param2) TestClass.new(param1).call(param2) end

# bad -- more verbose than necessary def self.call(param1, param2) self.new(param1).call(param2) end

# good def self.call(param1, param2) new(param1).call(param2) end

# ...other methods...

end

=== Defining Constants within a Block [[no-constant-definition-in-block]]

Do not define constants within a block, since the block's scope does not isolate or namespace the constant in any way.

Define the constant outside of the block instead, or use a variable or method if defining the constant in the outer scope would be problematic.

bad - FILESTOLINT is now defined globally

task :lint do FILESTOLINT = Dir['lib/*.rb'] # ... end

good - filestolint is only defined inside the block

task :lint do filestolint = Dir['lib/*.rb'] # ...

end

== Classes: Constructors

=== Factory Methods [[factory-methods]]

Consider adding factory methods to provide additional sensible ways to create instances of a particular class.

[source,ruby]

class Person def self.create(options_hash) # body omitted end

end

=== Disjunctive Assignment in Constructor [[disjunctive-assignment-in-constructor]]

In constructors, avoid unnecessary disjunctive assignment (

||=
) of instance variables. Prefer plain assignment. In ruby, instance variables (beginning with an
@
) are nil until assigned a value, so in most cases the disjunction is unnecessary.

[source,ruby]

def initialize @x ||= 1 end

good

def initialize @x = 1

end

[quote, Steve McConnell]

Good code is its own best documentation. As you're about to add a comment, ask yourself, "How can I improve the code so that this comment isn't needed?". Improve the code and then document it to make it even clearer.

Write self-documenting code and ignore the rest of this section. Seriously!

If the how can be made self-documenting, but not the why (e.g. the code works around non-obvious library behavior, or implements an algorithm from an academic paper), add a comment explaining the rationale behind the code.

[source,ruby]

x = BuggyClass.something.dup

def computedependencygraph ...30 lines of recursive graph merging... end

BuggyClass returns an internal object, so we have to dup it to modify it.

x = BuggyClass.something.dup

This is algorithm 6.4(a) from Worf & Yar's Amazing Graph Algorithms (2243).

def computedependencygraph ...30 lines of recursive graph merging...

end

=== Hash Space [[hash-space]]

Use one space between the leading

#
character of the comment and the text of the comment.

=== English Syntax [[english-syntax]]

Comments longer than a word are capitalized and use punctuation. Use https://en.wikipedia.org/wiki/Sentence_spacing[one space] after periods.

counter += 1 # Increments counter by one.

=== Comment Upkeep [[comment-upkeep]]

Keep existing comments up-to-date. An outdated comment is worse than no comment at all.

=== Refactor, Don't Comment [[refactor-dont-comment]]

[quote, old programmers maxim, 'http://eloquentruby.com/blog/2011/03/07/good-code-and-good-jokes/[through Russ Olsen]']

Good code is like a good joke: it needs no explanation.

Avoid writing comments to explain bad code. Refactor the code to make it self-explanatory. ("Do or do not - there is no try." Yoda)

== Comment Annotations

=== Annotations Placement [[annotate-above]]

Annotations should usually be written on the line immediately above the relevant code.

[source,ruby]

def bar baz(:quux) # FIXME: This has crashed occasionally since v3.2.1. end

good

def bar # FIXME: This has crashed occasionally since v3.2.1. baz(:quux)

end

=== Annotations Keyword Format [[annotate-keywords]]

The annotation keyword is followed by a colon and a space, then a note describing the problem.

[source,ruby]

def bar # FIXME This has crashed occasionally since v3.2.1. baz(:quux) end

good

def bar # FIXME: This has crashed occasionally since v3.2.1. baz(:quux)

end

=== Multi-line Annotations Indentation [[indent-annotations]]

If multiple lines are required to describe the problem, subsequent lines should be indented three spaces after the

#
(one general plus two for indentation purpose).

[source,ruby]

def bar # FIXME: This has crashed occasionally since v3.2.1. It may # be related to the BarBazUtil upgrade. baz(:quux)

end

=== Inline Annotations [[rare-eol-annotations]]

In cases where the problem is so obvious that any documentation would be redundant, annotations may be left at the end of the offending line with no note. This usage should be the exception and not the rule.

[source,ruby]

def bar sleep 100 # OPTIMIZE

end

===

TODO
[[todo]]

Use

TODO
to note missing features or functionality that should be added at a later date.

===

FIXME
[[fixme]]

Use

FIXME
to note broken code that needs to be fixed.

===

OPTIMIZE
[[optimize]]

Use

OPTIMIZE
to note slow or inefficient code that may cause performance problems.

===

HACK
[[hack]]

Use

HACK
to note code smells where questionable coding practices were used and should be refactored away.

===

REVIEW
[[review]]

Use

REVIEW
to note anything that should be looked at to confirm it is working as intended. For example:
REVIEW: Are we sure this is how the client does X currently?

=== Document Annotations [[document-annotations]]

Use other custom annotation keywords if it feels appropriate, but be sure to document them in your project's

README
or similar.

Place magic comments above all code and documentation in a file (except shebangs, which are discussed next).

class Person end

frozenstringliteral: true

class Person

end

=== Below Shebang [[below-shebang]]

Place magic comments below shebangs when they are present in a file.

App.parse(ARGV)

frozenstringliteral: true

App.parse(ARGV)

=== One Magic Comment per Line [[one-magic-comment-per-line]]

Use one magic comment per line if you need multiple.

encoding: ascii-8bit

Separate magic comments from code and documentation with a blank line.

Some documentation for Person

class Person # Some code end

Some documentation for Person

class Person # Some code

end

== Collections

=== Literal Array and Hash [[literal-array-hash]]

Prefer literal array and hash creation notation (unless you need to pass parameters to their constructors, that is).

[source,ruby]

arr = Array.new hash = Hash.new

good

arr = [] arr = Array.new(10) hash = {}

hash = Hash.new(0)

===

%w
[[percent-w]]

Prefer

%w
to the literal array syntax when you need an array of words (non-empty strings without spaces and special characters in them). Apply this rule only to arrays with two or more elements.

[source,ruby]

STATES = ['draft', 'open', 'closed']

good

STATES = %w[draft open closed]

===

%i
[[percent-i]]

Prefer

%i
to the literal array syntax when you need an array of symbols (and you don't need to maintain Ruby 1.9 compatibility). Apply this rule only to arrays with two or more elements.

[source,ruby]

STATES = [:draft, :open, :closed]

good

STATES = %i[draft open closed]

=== No Trailing Array Commas [[no-trailing-array-commas]]

Avoid comma after the last item of an

Array
or
Hash
literal, especially when the items are not on separate lines.

[source,ruby]

VALUES = [ 1001, 2020, 3333, ]

VALUES = [1001, 2020, 3333, ]

good

VALUES = [1001, 2020, 3333]

=== No Gappy Arrays [[no-gappy-arrays]]

Avoid the creation of huge gaps in arrays.

arr = []

arr[100] = 1 # now you have an array with lots of nils

===

first
and
last
[[first-and-last]]

When accessing the first or last element from an array, prefer

first
or
last
over
[0]
or
[-1]
.

=== Set vs Array [[set-vs-array]]

Use

Set
Array
when dealing with unique elements.
Set
implements a collection of unordered values with no duplicates. This is a hybrid of
Array
's intuitive inter-operation facilities and
Hash
's fast lookup.

=== Symbols as Keys [[symbols-as-keys]]

Prefer symbols instead of strings as hash keys.

[source,ruby]

hash = { 'one' => 1, 'two' => 2, 'three' => 3 }

good

hash = { one: 1, two: 2, three: 3 }

=== No Mutable Keys [[no-mutable-keys]]

Avoid the use of mutable objects as hash keys.

=== Hash Literals [[hash-literals]]

Use the Ruby 1.9 hash literal syntax when your hash keys are symbols.

[source,ruby]

hash = { :one => 1, :two => 2, :three => 3 }

good

hash = { one: 1, two: 2, three: 3 }

=== Hash Literal as Last Array Item [[hash-literal-as-last-array-item]]

Wrap hash literal in braces if it is a last array item.

[source,ruby]

[1, 2, one: 1, two: 2]

good

[1, 2, { one: 1, two: 2 }]

=== No Mixed Hash Syntaxes [[no-mixed-hash-syntaxes]]

Don't mix the Ruby 1.9 hash syntax with hash rockets in the same hash literal. When you've got keys that are not symbols stick to the hash rockets syntax.

[source,ruby]

{ a: 1, 'b' => 2 }

good

{ :a => 1, 'b' => 2 }

===

Hash#key?
[[hash-key]]

Use

Hash#key?
Hash#has_key?
and
Hash#value?
Hash#has_value?
.

good

hash.key?(:test)

hash.value?(value)

===

Hash#each
[[hash-each]]

Use

Hash#each_key
Hash#keys.each
and
Hash#each_value
Hash#values.each
.

[source,ruby]

hash.keys.each { |k| p k } hash.values.each { |v| p v } hash.each { |k, v| p k } hash.each { |k, v| p v }

good

hash.each_key { |k| p k }

hash.each_value { |v| p v }

===

Hash#fetch
[[hash-fetch]]

Use

Hash#fetch
when dealing with hash keys that should be present.

[source,ruby]

heroes = { batman: 'Bruce Wayne', superman: 'Clark Kent' }

bad - if we make a mistake we might not spot it right away

heroes[:batman] # => 'Bruce Wayne' heroes[:supermann] # => nil

good - fetch raises a KeyError making the problem obvious

heroes.fetch(:supermann)

===

Hash#fetch
defaults [[hash-fetch-defaults]]

Introduce default values for hash keys via

Hash#fetch
as opposed to using custom logic.

[source,ruby]

batman = { name: 'Bruce Wayne', is_evil: false }

bad - if we just use || operator with falsy value we won't get the expected result

batman[:is_evil] || true # => true

good - fetch works correctly with falsy values

batman.fetch(:is_evil, true) # => false

=== Use Hash Blocks [[use-hash-blocks]]

Prefer the use of the block instead of the default value in

Hash#fetch
if the code that has to be evaluated may have side effects or be expensive.

[source,ruby]

batman = { name: 'Bruce Wayne' }

so it can slow the program down if done multiple times

batman.fetch(:powers, obtainbatmanpowers) # obtainbatmanpowers is an expensive call

good - blocks are lazy evaluated, so only triggered in case of KeyError exception

batman.fetch(:powers) { obtainbatmanpowers }

===

Hash#values_at
[[hash-values-at]]

Use

Hash#values_at
when you need to retrieve several values consecutively from a hash.

[source,ruby]

email = data['email'] username = data['nickname']

good

===

Hash#transform_keys
and
Hash#transform_values
[[hash-transform-methods]]

Prefer

transform_keys
or
transform_values
over
each_with_object
or
map
when transforming just the keys or just the values of a hash.

[source,ruby]

{a: 1, b: 2}.eachwithobject({}) { |(k, v), h| h[k] = v * v } {a: 1, b: 2}.map { |k, v| [k.tos, v] }.toh

good

{a: 1, b: 2}.transform_values { |v| v * v }

{a: 1, b: 2}.transformkeys { |k| k.tos }

=== Ordered Hashes [[ordered-hashes]]

Rely on the fact that as of Ruby 1.9 hashes are ordered.

=== No Modifying Collections [[no-modifying-collections]]

Do not modify a collection while traversing it.

=== Accessing Elements Directly [[accessing-elements-directly]]

When accessing elements of a collection, avoid direct access via

[n]
by using an alternate form of the reader method if it is supplied. This guards you from calling
[]
on
nil
.

[source,ruby]

Regexp.last_match[1]

good

Regexp.last_match(1)

=== Provide Alternate Accessor to Collections [[provide-alternate-accessor-to-collections]]

When providing an accessor for a collection, provide an alternate form to save users from checking for

nil
before accessing an element in the collection.

[source,ruby]

def awesomethings @awesomethings end

good

def awesomethings(index = nil) if index && @awesomethings @awesomethings[index] else @awesomethings end

end

===

map
/
find
/
select
/
reduce
/
include?
/
size
[[map-find-select-reduce-include-size]]

Prefer

map
over
collect
,
find
over
detect
,
select
over
find_all
,
reduce
over
inject
,
include?
over
member?
and
size
over
length
. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it. The rhyming methods are inherited from Smalltalk and are not common in other programming languages. The reason the use of
select
is encouraged over
find_all
is that it goes together nicely with
reject
and its name is pretty self-explanatory.

===

count
vs
size
[[count-vs-size]]

Don't use

count
as a substitute for
size
. For
Enumerable
objects other than
Array
it will iterate the entire collection in order to determine its size.

some_hash.count

good

some_hash.size

===

flat_map
[[flat-map]]

Use

flat_map
map
+
flatten
. This does not apply for arrays with a depth greater than 2, i.e. if
users.first.songs == ['a', ['b','c']]
, then use
map + flatten
rather than
flat_map
.
flat_map
flattens the array by 1, whereas
flatten
flattens it all the way.

[source,ruby]

all_songs = users.map(&:songs).flatten.uniq

good

allsongs = users.flatmap(&:songs).uniq

===

reverse_each
[[reverse-each]]

Prefer

reverse_each
to
reverse.each
because some classes that
include Enumerable
will provide an efficient implementation. Even in the worst case where a class does not provide a specialized implementation, the general implementation inherited from
Enumerable
will be at least as efficient as using
reverse.each
.

[source,ruby]

array.reverse.each { ... }

good

array.reverse_each { ... }

== Numbers

=== Underscores in Numerics [[underscores-in-numerics]]

num = 1000000

good - much easier to parse for the human brain

num = 1000000

=== Numeric Literal Prefixes [[numeric-literal-prefixes]]

Prefer lowercase letters for numeric literal prefixes.

0o
for octal,
0x
0b
for binary. Do not use
0d
prefix for decimal literals.

[source,ruby]

num = 01234 num = 0O1234 num = 0X12AB num = 0B10101 num = 0D1234 num = 0d1234

good - easier to separate digits from the prefix

num = 0o1234 num = 0x12AB num = 0b10101

num = 1234

=== Integer Type Checking [[integer-type-checking]]

Use

Integer
to check type of an integer number. Since
Fixnum
is platform-dependent, checking against it will return different results on 32-bit and 64-bit machines.

[source,ruby]

timestamp = Time.now.to_i

timestamp.isa?(Fixnum) timestamp.isa?(Bignum)

good

timestamp.is_a?(Integer)

=== Random Numbers [[random-numbers]]

Prefer to use ranges when generating random numbers instead of integers with offsets, since it clearly states your intentions. Imagine simulating a roll of a dice:

rand(6) + 1

good

rand(1..6)

=== Float Division [[float-division]]

When performing float-division on two integers, either use

fdiv
or convert one-side integer to float.

a.tof / b.tof

good

a.tof / b a / b.tof

a.fdiv(b)

=== Float Comparison [[float-comparison]]

Avoid (in)equality comparisons of floats as they are unreliable.

Floating point values are inherently inaccurate, and comparing them for exact equality is almost never the desired semantics. Comparison via the

==/!=
operators checks floating-point value representation to be exactly the same, which is very unlikely if you perform any arithmetic operations involving precision loss.

[source,ruby]

x == 0.1 x != 0.1

x.tod == 0.1.tod

good - not an actual float comparison

x == Float::INFINITY

good

(x - 0.1).abs < Float::EPSILON

good

tolerance = 0.0001 (x - 0.1).abs < tolerance

https://www.embeddeduse.com/2019/08/26/qt-compare-two-floats/

=== Exponential Notation [[exponential-notation]]

When using exponential notation for numbers, prefer using the normalized scientific notation, which uses a mantissa between 1 (inclusive) and 10 (exclusive). Omit the exponent altogether if it is zero.

The goal is to avoid confusion between powers of ten and exponential notation, as one quickly reading

10e7
could think it's 10 to the power of 7 (one then 7 zeroes) when it's actually 10 to the power of 8 (one then 8 zeroes). If you want 10 to the power of 7, you should do
1e7
.

| power notation | exponential notation | output | |----------------|----------------------|----------| | 10 ** 7 | 1e7 | 10000000 | | 10 ** 6 | 1e6 | 1000000 | | 10 ** 7 | 10e6 | 10000000 |

One could favor the alternative engineering notation, in which the exponent must always be a multiple of 3 for easy conversion to the thousand / million / ... system.

[source,ruby]

10e6 0.3e4 11.7e5 3.14e0

good

1e7 3e3 1.17e6

3.14

Alternative : engineering notation:

3.2e7 0.1e5 12e4

good

1e6 17e6

0.98e9

== Strings

=== String Interpolation [[string-interpolation]]

Prefer string interpolation and string formatting to string concatenation:

[source,ruby]

emailwithname = user.name + ' <' + user.email + '>'

good

emailwithname = "#{user.name} <#{user.email}>"

good

emailwithname = format('%s <%s>', user.name, user.email)

=== Consistent String Literals [[consistent-string-literals]]

Adopt a consistent string literal quoting style. There are two popular styles in the Ruby community, both of which are considered good - single quotes by default and double quotes by default.

NOTE: The string literals in this guide are using single quotes by default.

==== Single Quote [[consistent-string-literals-single-quote]]

Prefer single-quoted strings when you don't need string interpolation or special symbols such as

\t
,
\n
,
'
, etc.

[source,ruby]

name = "Bozhidar"

name = 'De\'Andre'

good

name = 'Bozhidar'

name = "De'Andre"

==== Double Quote [[consistent-string-literals-double-quote]]

Prefer double-quotes unless your string literal contains " or escape characters you want to suppress.

[source,ruby]

name = 'Bozhidar'

sarcasm = "I \"like\" it."

good

name = "Bozhidar"

sarcasm = 'I "like" it.'

=== No Character Literals [[no-character-literals]]

Don't use the character literal syntax

?x
. Since Ruby 1.9 it's basically redundant -
?x
would be interpreted as
'x'
(a string with a single character in it).

char = ?c

good

char = 'c'

=== Curlies Interpolate [[curlies-interpolate]]

Don't leave out

{}
around instance and global variables being interpolated into a string.

[source,ruby]

def initialize(firstname, lastname) @firstname = firstname @lastname = lastname end

# bad - valid, but awkward def tos "#@firstname #@last_name" end

# good def tos "#{@firstname} #{@last_name}" end end

,

good

process Regexp.last_match(1)

=== Avoid Numbered Groups [[no-numbered-regexes]]

Avoid using numbered groups as it can be hard to track what they contain. Named groups can be used instead.

[source,ruby]

/(regexp)/ =~ string

some code

process Regexp.last_match(1)

good

/(?regexp)/ =~ string

some code

process meaningful_var

=== Limit Escapes [[limit-escapes]]

Character classes have only a few special characters you should care about:

^
,
-
,
\
,
]
, so don't escape
.
or brackets in
[]
.

=== Caret and Dollar Regexp [[caret-and-dollar-regexp]]

Be careful with

^
and
$ as they match start/end of line, not string endings. If you want to match the whole string use: \A and \z (not to be confused with \Z which is the equivalent of /\n?\z/ ). [source,ruby] string = "some injection\nusername" string[/^username$/] # matches

=== Multi-line Regular Expressions [[multi-line-regexes]]

Use

x
(free-spacing) modifier for multi-line regexps.

NOTE: That's known as http://www.regular-expressions.info/freespacing.html[free-spacing mode]. In this mode leading and trailing whitespace is ignored.

[source,ruby]

regex = /start\ \s\ (group)\ (?:alt1|alt2)\ end/

good

regexp = / start \s (group) (?:alt1|alt2) end

/x

=== Comment Complex Regular Expressions [[comment-regexes]]

Use

x

[source,ruby]

regexp = / start # some text \s # white space char (group) # first group (?:alt1|alt2) # some alternation end

/x

=== Use

gsub
with a Block or a Hash for Complex Replacements [[gsub-blocks]]

For complex replacements

sub
/
gsub
can be used with a block or a hash.

[source,ruby]

words = 'foo bar' words.sub(/f/, 'f' => 'F') # => 'Foo bar'

words.gsub(/\w+/) { |word| word.capitalize } # => 'Foo Bar'

== Percent Literals

===

%q
shorthand [[percent-q-shorthand]]

Use

%()
(it's a shorthand for
%Q
) for single-line strings which require both interpolation and embedded double-quotes. For multi-line strings, prefer heredocs.

%(

Some text
)

should be 'Some text'

%(This is #{quality} style)

should be "This is #{quality} style"

%(

\n#{exclamation}\n
)

good (requires interpolation, has quotes, single line)

[source,ruby]

name = %q(Bruce Wayne) time = %q(8 o'clock) question = %q("What did you say?")

good

name = 'Bruce Wayne' time = "8 o'clock" question = '"What did you say?"'

quote = %q(

"What did you say?"

)

===

%r
[[percent-r]]

Use

%r
only for regular expressions matching at least one
/
character.

%r{\s+}

good

%r{^/(.*)$} %r{^/blog/2011/(.*)$}

===

%x
[[percent-x]]

Avoid the use of

%x
unless you're going to invoke a command with backquotes in it (which is rather unlikely).

date = %x(date)

good

date =

date

echo = %x(echo date)

===

%s
[[percent-s]]

Avoid the use of

%s
. It seems that the community has decided
:"some string"
is the preferred way to create a symbol with spaces in it.

=== Percent Literal Braces [[percent-literal-braces]]

Use the braces that are the most appropriate for the various kinds of percent literals.

• ()
for string literals (
%q
,
%Q
).
• []
for array literals (
%w
,
%i
,
%W
,
%I
) as it is aligned with the standard array literals.
• {}
for regexp literals (
%r
) since parentheses often appear inside regular expressions. That's why a less common character with
{
is usually the best delimiter for
%r
literals.
• ()
for all other literals (e.g.
%s
,
%x
)

[source,ruby]

%q{"Test's king!", John said.}

good

%q("Test's king!", John said.)

%w(one two three) %i(one two three)

good

%w[one two three] %i[one two three]

%r((\w+)-(\d+)) %r{\w{1,2}\d{2,5}}

good

%r{(\w+)-(\d+)}

%r|\w{1,2}\d{2,5}|

== Metaprogramming

=== No Needless Metaprogramming [[no-needless-metaprogramming]]

Avoid needless metaprogramming.

=== No Monkey Patching [[no-monkey-patching]]

Do not mess around in core classes when writing libraries (do not monkey-patch them).

=== Block

class_eval
[[block-class-eval]]

The block form of

class_eval
is preferable to the string-interpolated form.

==== Supply Location [[class-eval-supply-location]]

When you use the string-interpolated form, always supply

+__FILE__+
and
+__LINE__+
, so that your backtraces make sense:

classeval 'def userelativemodelnaming?; true; end', FILE, LINE

====

define_method
[[class-eval-define_method]]

define_method
is preferable to
class_eval { def ... }

===

eval
Comment Docs [[eval-comment-docs]]

When using

class_eval
(or other
eval
) with string interpolation, add a comment block showing its appearance if interpolated (a practice used in Rails code):

from activesupport/lib/activesupport/coreext/string/output_safety.rb

UNSAFESTRINGMETHODS.each do |unsafemethod| if 'String'.respondto?(unsafemethod) classeval <<-EOT, FILE, LINE + 1 def #{unsafemethod}(params, &block) # def capitalize(params, &block) tostr.#{unsafemethod}(*params, &block) # tostr.capitalize(*params, &block) end # end

  def #{unsafe_method}!(*params)              # def capitalize!(*params)
@dirty = true                             #   @dirty = true
super                                     #   super
end                                         # end
EOT


end

end

=== No

method_missing
[[no-method-missing]]

Avoid using

method_missing
for metaprogramming because backtraces become messy, the behavior is not listed in
#methods
, and misspelled method calls might silently work, e.g.
nukes.luanch_state = false
. Consider using delegation, proxy, or
define_method
method_missing
:
• Be sure to http://blog.marc-andre.ca/2010/11/methodmissing-politely.html[also define
respond_to_missing?
]
• Only catch methods with a well-defined prefix, such as
find_by_*
--make your code as assertive as possible.
• Call
super
at the end of your statement
• Delegate to assertive, non-magical methods:

[source,ruby]

def methodmissing(meth, *params, &block) if /^findby(?.*)/ =~ meth # ... lots of code to do a findby else super end end

good

def methodmissing(meth, *params, &block) if /^findby(?.*)/ =~ meth findby(prop, *params, &block) else super end end

best of all, though, would to define_method as each findable attribute is declared

=== Prefer

public_send
[[prefer-public-send]]

Prefer

public_send
over
send
so as not to circumvent
private
/
protected
visibility.

We have an ActiveModel Organization that includes concern Activatable

module Activatable extend ActiveSupport::Concern

included do beforecreate :createtoken end

private

def reset_token # some code end

def create_token # some code end

def activate! # some code end end

class Organization < ActiveRecord::Base include Activatable end

linux_organization = Organization.find(...)

linuxorganization.send(:resettoken)

GOOD - should throw an exception

linuxorganization.publicsend(:reset_token)

=== Prefer

+__send__+
[[prefer-send]]

Prefer

+__send__+
over
send
, as
send
may overlap with existing methods.

[source,ruby]

require 'socket'

u1 = UDPSocket.new u1.bind('127.0.0.1', 4913) u2 = UDPSocket.new u2.connect('127.0.0.1', 4913)

Instead it will send a message via UDP socket.

u2.send :sleep, 0

Will actually send a message to the receiver obj.

u2.send ...

== API Documentation [[api-documentation]]

=== YARD

Use https://yardoc.org/[YARD] and its conventions for API documentation.

Don't use block comments. They cannot be preceded by whitespace and are not as easy to spot as regular comments.

[source,ruby]

=begin comment line another comment line =end

another comment line

.From Perl's POD to RD

This is not a really a block comment syntax, but more of an attempt to emulate Perl's https://perldoc.perl.org/perlpod.html[POD] documentation system.

There's an https://github.com/uwabami/rdtool[rdtool] for Ruby that's pretty similar to POD. Basically

rdtool
scans a file for
=begin
and
=end
pairs, and extracts the text between them all. This text is assumed to be documentation in https://github.com/uwabami/rdtool/blob/master/doc/rd-draft.rd[RD format]. You can read more about it https://ruby-doc.com/docs/ProgrammingRuby/html/rdtool.html[here].

RD predated the rise of RDoc and YARD and was effectively obsoleted by them.footnote:[According to this https://en.wikipedia.org/wiki/RubyDocumentformat[Wikipedia article] the format used to be popular until the early 2000s when it was superseded by RDoc.]

== Gemfile and Gemspec

=== No

RUBY_VERSION
in the gemspec [[no-ruby-version-in-the-gemspec]]

The gemspec should not contain

RUBY_VERSION
as a condition to switch dependencies.
RUBY_VERSION
is determined by
rake release
, so users may end up with wrong dependency.

[source,ruby]

Gem::Specification.new do |s| if RUBYVERSION >= '2.5' s.addruntimedependency 'gema' else s.addruntimedependency 'gem_b' end

end

Fix by either:

• Post-install messages.
• Add both gems as dependency (if permissible).
• If development dependencies, move to Gemfile.

== Misc

=== No Flip-flops [[no-flip-flops]]

Avoid the use of flip-flops.

NOTE: They are deprecated as of Ruby 2.6.

=== No non-

nil
Checks [[no-non-nil-checks]]

Don't do explicit non-

nil
checks unless you're dealing with boolean values.

[source,ruby]

dosomething if !something.nil? dosomething if something != nil

good

do_something if something

good - dealing with a boolean

def valueset? [email protected]boolean.nil?

end

=== Global Input/Output Streams [[global-stdout]]

Use

$stdout/$stderr/$stdin instead of STDOUT/STDERR/STDIN . STDOUT/STDERR/STDIN are constants, and while you can actually reassign (possibly to redirect some stream) constants in Ruby, you'll get an interpreter warning if you do so. [source,ruby] bad STDOUT.puts('hello') hash = { out: STDOUT, key: value } def m(out = STDOUT) out.puts('hello') end good$stdout.puts('hello')

hash = { out: $stdout, key: value } def m(out =$stdout) out.puts('hello')

end

NOTE: The only valid use-case for the stream constants is obtaining references to the original streams (assuming you've redirected some of the global vars).

=== Warn [[warn]]

Use

warn

good

warn 'This is a warning!'

===

Array#join
[[array-join]]

Prefer the use of

Array#join
over the fairly cryptic
Array#*
with a string argument.

[source,ruby]

%w[one two three] * ', '

good

%w[one two three].join(', ')

=> 'one, two, three'

=== Array Coercion [[array-coercion]]

Use

Array()
Array
check or
[*var]
, when dealing with a variable you want to treat as an Array, but you're not certain it's an array.

[source,ruby]

paths = [paths] unless paths.isa?(Array) paths.each { |path| dosomething(path) }

bad (always creates a new Array instance)

[*paths].each { |path| do_something(path) }

good (and a bit more readable)

Array(paths).each { |path| do_something(path) }

=== Ranges or

between
[[ranges-or-between]]

Use ranges or

Comparable#between?
instead of complex comparison logic when possible.

[source,ruby]

do_something if x >= 1000 && x <= 2000

good

do_something if (1000..2000).include?(x)

good

do_something if x.between?(1000, 2000)

=== Predicate Methods [[predicate-methods]]

Prefer the use of predicate methods to explicit comparisons with

==
. Numeric comparisons are OK.

[source,ruby]

if x % 2 == 0 end

if x % 2 == 1 end

if x == nil end

good

if x.even? end

if x.odd? end

if x.nil? end

if x.zero? end

if x == 0

end

=== No Cryptic Perlisms [[no-cryptic-perlisms]]

Avoid using Perl-style special variables (like

$: , $;
, etc). They are quite cryptic and their use in anything but one-liner scripts is discouraged.

$:.unshift File.dirname(FILE) good $LOADPATH.unshift File.dirname(FILE_)

Use the human-friendly aliases provided by the

English
library if required.

print $',$$good require 'English' print$POSTMATCH, $PID === Use require_relative whenever possible For all your internal dependencies, you should use require_relative . Use of require should be reserved for external dependencies [source,ruby] bad require 'set' require 'mygem/spec/helper' require 'mygem/lib/something' good require 'set' require_relative 'helper' require_relative '../lib/something' This way is more expressive (making clear which dependency is internal or not) and more efficient (as require_relative doesn't have to try all of $LOAD_PATH
contrary to
require
).

=== Always Warn [[always-warn]]

Write

ruby -w
safe code.

=== No Optional Hash Params [[no-optional-hash-params]]

Avoid hashes as optional parameters. Does the method do too much? (Object initializers are exceptions for this rule).

=== Instance Vars [[instance-vars]]

Use module instance variables instead of global variables.

\$foo_bar = 1

good

module Foo class << self attr_accessor :bar end end

Foo.bar = 1

===

OptionParser
[[optionparser]]

Use

OptionParser
for parsing complex command line options and
ruby -s
for trivial command line options.

=== No Param Mutations [[no-param-mutations]]

Do not mutate parameters unless that is the purpose of the method.

=== Three is the Number Thou Shalt Count [[three-is-the-number-thou-shalt-count]]

Avoid more than three levels of block nesting.

=== Functional Code [[functional-code]]

Code in a functional way, avoiding mutation when that makes sense.

[source,ruby]

a = []; [1, 2, 3].each { |i| a << i * 2 } # bad a = [1, 2, 3].map { |i| i * 2 } # good

a = {}; [1, 2, 3].each { |i| a[i] = i * 17 } # bad a = [1, 2, 3].reduce({}) { |h, i| h[i] = i * 17; h } # good

a = [1, 2, 3].eachwithobject({}) { |i, h| h[i] = i * 17 } # good

=== No explicit

.rb
to
require
[[no-explicit-rb-to-require]]

Omit the

.rb
extension for filename passed to
require
and
require_relative
.

NOTE: If the extension is omitted, Ruby tries adding '.rb', '.so', and so on to the name until found. If the file named cannot be found, a

LoadError
will be raised. There is an edge case where
foo.so
LoadError
if
foo.so
file exists when
require 'foo.rb'
will be changed to
require 'foo'`
, but that seems harmless.

[source,ruby]

require 'foo.rb' require_relative '../foo.rb'

good

require 'foo' require 'foo.so' require_relative '../foo'

require_relative '../foo.so'

== Tools

Here are some tools to help you automatically check Ruby code against this guide.

=== RuboCop

https://github.com/rubocop-hq/rubocop[RuboCop] is a Ruby static code analyzer and formatter, based on this style guide. RuboCop already covers a significant portion of the guide and has https://docs.rubocop.org/en/stable/integrationwithother_tools/[plugins] for most popular Ruby editors and IDEs.

TIP: RuboCop's cops (code checks) have links to the guidelines that they are based on, as part of their metadata.

=== RubyMine

http://www.jetbrains.com/ruby/[RubyMine]'s code inspections are http://confluence.jetbrains.com/display/RUBYDEV/RubyMine+Inspections[partially based] on this guide.

== History

This guide started its life as an internal company Ruby coding guidelines (written by https://github.com/bbatsov[Bozhidar Batsov]). Bozhidar had always been bothered as a Ruby developer about one thing - Python developers had a great programming style reference (https://www.python.org/dev/peps/pep-0008/[PEP-8]) and Rubyists never got an official guide, documenting Ruby coding style and best practices. Bozhidar firmly believed that style matters. He also believed that a great hacker community, such as Ruby has, should be quite capable of producing this coveted document. The rest is history...

At some point Bozhidar decided that the work he was doing might be interesting to members of the Ruby community in general and that the world had little need for another internal company guideline. But the world could certainly benefit from a community-driven and community-sanctioned set of practices, idioms and style prescriptions for Ruby programming.

Bozhidar served as the guide's only editor for a few years, before a team of editors was formed once the project transitioned to RuboCop HQ.

Since the inception of the guide we've received a lot of feedback from members of the exceptional Ruby community around the world. Thanks for all the suggestions and the support! Together we can make a resource beneficial to each and every Ruby developer out there.

== Sources of Inspiration

Many people, books, presentations, articles and other style guides influenced the community Ruby style guide. Here are some of them:

• https://en.wikipedia.org/wiki/TheElementsof_Style[The Elements of Style]
• https://en.wikipedia.org/wiki/TheElementsofProgrammingStyle[The Elements of Programming Style]
• https://www.python.org/dev/peps/pep-0008/[PEP-8]
• https://pragprog.com/book/ruby4/programming-ruby-1-9-2-0["Programming Ruby"]
• http://www.amazon.com/Ruby-Programming-Language-David-Flanagan/dp/0596516177["The Ruby Programming Language"]

== Contributing

The guide is still a work in progress - some guidelines are lacking examples, some guidelines don't have examples that illustrate them clearly enough. Improving such guidelines is a great (and simple way) to help the Ruby community!

In due time these issues will (hopefully) be addressed - just keep them in mind for now.

Nothing written in this guide is set in stone. It's our desire to work together with everyone interested in Ruby coding style, so that we could ultimately create a resource that will be beneficial to the entire Ruby community.

Feel free to open tickets or send pull requests with improvements. Thanks in advance for your help!

You can also support the project (and RuboCop) with financial contributions via https://www.patreon.com/bbatsov[Patreon].

=== How to Contribute?

It's easy, just follow the contribution guidelines below:

• https://help.github.com/articles/fork-a-repo[Fork] https://github.com/rubocop-hq/ruby-style-guide[rubocop-hq/ruby-style-guide] on GitHub
• Make your feature addition or bug fix in a feature branch.
• Push your feature branch to GitHub
• Send a https://help.github.com/articles/using-pull-requests[Pull Request]

== Colophon

This guide is written in http://asciidoc.org/[AsciiDoc] and is published as HTML using https://asciidoctor.org/[AsciiDoctor]. The HTML version of the guide is hosted on GitHub Pages.

Originally the guide was written in Markdown, but was converted to AsciiDoc in 2019.