This Ruby style guide is the official reference for all of Voxable's Ruby projects. It 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.
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.
This style guide evolves over time as additional conventions are identified and past conventions are rendered obsolete by changes in Ruby itself.
This repo's .rubocop.yml file encodes this style guide as a RuboCop configuration. To include it in your project, add the following to the top of your project's .rubocop.yml:
inherit_from:
- https://raw.githubusercontent.com/voxable-labs/ruby-style-guide/master/.rubocop.yml
You'll also want to add its cache file to your .gitignore:
# RuboCop config cache file
.rubocop-https---raw-githubusercontent-com-voxable-labs-ruby-style-guide-master--rubocop-yml
If you need to bust this cache file to pick up the latest changes to the guide (which should happen automatically every 24 hours), you can simply delete the cache file from your project.
We didn't come up with all the rules out of nowhere. In fact, this repo started life as a fork of bbatsov's excellent ruby-style-guide, with a few changes
that happen to suit our tastes.
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...
-- Jerry Coffin (on indentation)
Use UTF-8 as the source file encoding.
[link]
Use two spaces per indentation level (aka soft tabs). No hard tabs. [link]
# bad - four spaces
def some_method
do_something
end
# good
def some_method
do_something
end
Use Unix-style line endings. (*BSD/Solaris/Linux/macOS users are covered by default, Windows users have to be extra careful.) [link]
If you're using Git you might want to add the following configuration setting to protect your project from Windows line endings creeping in:
$ git config --global core.autocrlf true
Don't use ; to separate statements and expressions. As a corollary—use
one expression per line.
[link]
# bad
puts 'foobar'; # superfluous semicolon
puts 'foo'; puts 'bar' # two expressions on the same line
# good
puts 'foobar'
puts 'foo'
puts 'bar'
puts 'foo', 'bar' # this applies to puts in particular
Prefer a single-line format for class definitions with no body. [link]
# bad
class FooError < StandardError
end
# okish
class FooError < StandardError; end
# good
FooError = Class.new(StandardError)
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. [link]
# bad
def too_much; something; something_else; end
# okish - notice that the first ; is required
def no_braces_method; body end
# okish - notice that the second ; is optional
def no_braces_method; 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
Use spaces around operators, after commas, colons and semicolons. Whitespace might be (mostly) irrelevant to the Ruby interpreter, but its proper use is the key to writing easily readable code. [link]
sum = 1 + 2
a, b = 1, 2
class FooError < StandardError; end
The only exception, regarding operators, is the exponent operator:
# bad
e = M * c ** 2
# good
e = M * c**2
No spaces after (, [ or before ], ).
Use spaces around { and before }.
[link]
# bad
some( arg ).other
[ 1, 2, 3 ].each{|e| puts e}
# good
some(arg).other
[1, 2, 3].each { |e| puts e }
{ and } deserve a bit of clarification, since they are used
for block and hash literals, as well as string interpolation.
For hash literals two styles are considered acceptable. The first variant is slightly more readable (and arguably more popular in the Ruby community in general). The second variant has the advantage of adding visual difference between block and hash literals. Whichever one you pick—apply it consistently.
# good - space after { and before }
{ one: 1, two: 2 }
# good - no space after { and before }
{one: 1, two: 2}
With interpolated expressions, there should be no padded-spacing inside the braces.
# bad
"From: #{ user.first_name }, #{ user.last_name }"
# good
"From: #{user.first_name}, #{user.last_name}"
No space after !.
[link]
# bad
! something
# good
!something
No space inside range literals. [link]
# bad
1 .. 3
'a' ... 'z'
# good
1..3
'a'...'z'
Indent when as deep as case. This is the style established in both
"The Ruby Programming Language" and "Programming Ruby".
[link]
# bad
case
when song.name == 'Misty'
puts 'Not again!'
when song.duration > 120
puts 'Too long!'
when Time.now.hour > 21
puts "It's too late"
else
song.play
end
# good
case
when song.name == 'Misty'
puts 'Not again!'
when song.duration > 120
puts 'Too long!'
when Time.now.hour > 21
puts "It's too late"
else
song.play
end
When assigning the result of a conditional expression to a variable, preserve the usual alignment of its branches. [link]
# bad - pretty convoluted
kind = case year
when 1850..1889 then 'Blues'
when 1890..1909 then 'Ragtime'
when 1910..1929 then 'New Orleans Jazz'
when 1930..1939 then 'Swing'
when 1940..1950 then 'Bebop'
else 'Jazz'
end
result = if some_cond
calc_something
else
calc_something_else
end
# good - it's apparent what's going on
kind = case year
when 1850..1889 then 'Blues'
when 1890..1909 then 'Ragtime'
when 1910..1929 then 'New Orleans Jazz'
when 1930..1939 then 'Swing'
when 1940..1950 then 'Bebop'
else 'Jazz'
end
result = if some_cond
calc_something
else
calc_something_else
end
# good (and a bit more width efficient)
kind =
case year
when 1850..1889 then 'Blues'
when 1890..1909 then 'Ragtime'
when 1910..1929 then 'New Orleans Jazz'
when 1930..1939 then 'Swing'
when 1940..1950 then 'Bebop'
else 'Jazz'
end
result =
if some_cond
calc_something
else
calc_something_else
end
Use empty lines between method definitions and also to break up methods into logical paragraphs internally. [link]
def some_method
data = initialize(options)
data.manipulate!
data.result
end
def some_method
result
end
Don't use several empty lines in a row. [link]
# bad - It has two empty lines.
some_method
some_method
# good
some_method
some_method
Use empty lines around access modifiers. [link]
# bad
class Foo
attr_reader :foo
def foo
# do something...
end
end
# good
class Foo
attr_reader :foo
def foo
# do something...
end
end
Don't use empty lines around method, class, module, block bodies. [link]
# bad
class Foo
def foo
begin
do_something do
something
end
rescue
something
end
end
end
# good
class Foo
def foo
begin
do_something do
something
end
rescue
something
end
end
end
Avoid comma after the last parameter in a method call, especially when the parameters are not on separate lines. [link]
# bad - easier to move/add/remove parameters, but still not preferred
some_method(
size,
count,
color,
)
# bad
some_method(size, count, color, )
# good
some_method(size, count, color)
Use spaces around the = operator when assigning default values to method
parameters:
[link]
# bad
def some_method(arg1=:default, arg2=nil, arg3=[])
# do something...
end
# good
def some_method(arg1 = :default, arg2 = nil, arg3 = [])
# do something...
end
While several Ruby books suggest the first style, the second is much more prominent in practice (and arguably a bit more readable).
Avoid line continuation \ where not required. In practice, avoid using
line continuations for anything but string concatenation.
[link]
# bad
result = 1 - \
2
# good (but still ugly as hell)
result = 1 \
- 2
long_string = 'First part of the long string' \
' and second part of the long string'
Adopt a consistent multi-line method chaining style. There are two popular
styles in the Ruby community, both of which are considered
good—leading . (Option A) and trailing . (Option B).
[link]
(Option A) When continuing a chained method invocation on
another line keep the . on the second line.
# bad - need to consult first line to understand second line
one.two.three.
four
# good - it's immediately clear what's going on the second line
one.two.three
.four
(Option B) When continuing a chained method invocation on another line,
include the . on the first line to indicate that the
expression continues.
# bad - need to read ahead to the second line to know that the chain continues
one.two.three
.four
# good - it's immediately clear that the expression continues beyond the first line
one.two.three.
four
A discussion on the merits of both alternative styles can be found here.
Align the parameters of a method call if they span more than one line. When aligning parameters is not appropriate due to line-length constraints, single indent for the lines after the first is also acceptable. [link]
# starting point (line is too long)
def send_mail(source)
Mailer.deliver(to: 'bob@example.com', from: 'us@example.com', subject: 'Important message', body: source.text)
end
# bad (double indent)
def send_mail(source)
Mailer.deliver(
to: 'bob@example.com',
from: 'us@example.com',
subject: 'Important message',
body: source.text)
end
# good
def send_mail(source)
Mailer.deliver(to: 'bob@example.com',
from: 'us@example.com',
subject: 'Important message',
body: source.text)
end
# good (normal indent)
def send_mail(source)
Mailer.deliver(
to: 'bob@example.com',
from: 'us@example.com',
subject: 'Important message',
body: source.text
)
end
Align the elements of array literals spanning multiple lines. [link]
# bad - single indent
menu_item = ['Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',
'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam']
# good
menu_item = [
'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',
'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam'
]
# good
menu_item =
['Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam',
'Baked beans', 'Spam', 'Spam', 'Spam', 'Spam', 'Spam']
Add underscores to large numeric literals to improve their readability. [link]
# bad - how many 0s are there?
num = 1000000
# good - much easier to parse for the human brain
num = 1_000_000
Prefer smallcase letters for numeric literal prefixes.
0o for octal, 0x for hexadecimal and 0b for binary.
Do not use 0d prefix for decimal literals.
[link]
# bad
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
Use [Rdoc][rdoc] and its conventions for API documentation. Don't put an
empty line between the comment block and the def.
[link]
Limit lines to 80 characters. [link]
Avoid trailing whitespace. [link]
End each file with a newline. [link]
Don't use block comments. They cannot be preceded by whitespace and are not as easy to spot as regular comments. [link]
# bad
=begin
comment line
another comment line
=end
# good
# comment line
# another comment line
Use :: only to reference constants(this includes classes and
modules) and constructors (like Array() or Nokogiri::HTML()).
Do not use :: for regular method invocation.
[link]
# bad
SomeClass::some_method
some_object::some_method
# good
SomeClass.some_method
some_object.some_method
SomeModule::SomeClass::SOME_CONST
SomeModule::SomeClass()
Use def with parentheses when there are parameters. Omit the
parentheses when the method doesn't accept any parameters.
[link]
# bad
def some_method()
# body omitted
end
# good
def some_method
# body omitted
end
# bad
def some_method_with_parameters param1, param2
# body omitted
end
# good
def some_method_with_parameters(param1, param2)
# body omitted
end
Use parentheses around the arguments of method invocations,
especially if the first argument begins with an open parenthesis (,
as in f((3 + 2) + 1).
[link]
# bad
x = Math.sin y
# good
x = Math.sin(y)
# bad
array.delete e
# good
array.delete(e)
# bad
temperance = Person.new 'Temperance', 30
# good
temperance = Person.new('Temperance', 30)
Only omit parentheses for
Method calls with no arguments:
# bad
Kernel.exit!()
2.even?()
fork()
'test'.upcase()
# good
Kernel.exit!
2.even?
fork
'test'.upcase
Methods that are part of an internal DSL (e.g., Rake, Rails, RSpec):
# bad
validates(:name, presence: true)
# good
validates :name, presence: true
Methods that have "keyword" status in Ruby:
class Person
# bad
attr_reader(:name, :age)
# good
attr_reader :name, :age
# body omitted
end
# bad
puts(temperance.age)
# good
puts temperance.age
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. [link]
# bad
def some_method(a = 1, b = 2, c, d)
puts "#{a}, #{b}, #{c}, #{d}"
end
some_method('w', 'x') # => '1, 2, w, x'
some_method('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
some_method('w', 'x') # => '1, 2, w, x'
some_method('w', 'x', 'y') # => 'y, 2, w, x'
some_method('w', 'x', 'y', 'z') # => 'y, z, w, x'
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. [link]
# bad
a, b, c, d = 'foo', 'bar', 'baz', 'foobar'
# good
a = 'foo'
b = 'bar'
c = 'baz'
d = 'foobar'
# good - swapping variable assignment
# Swapping variable assignment is a special case because it will allow you to
# 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]
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. [link]
# bad
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'
# The underscores are needed to show that you want all elements
# except for the last number of underscore elements
*beginning, _ = foo.split(',')
*beginning, something, _ = foo.split(',')
a, = foo.split(',')
a, b, = foo.split(',')
# Unnecessary assignment to an unused variable, but the assignment
# provides us with useful information.
first, _second = foo.split(',')
first, _second, = foo.split(',')
first, *_ending = foo.split(',')
Do not use for, unless you know exactly why. Most of the time iterators
should be used instead. for is implemented in terms of each (so you're
adding a level of indirection), but with a twist—for doesn't
introduce a new scope (unlike each) and variables defined in its block
will be visible outside it.
[link]
arr = [1, 2, 3]
# bad
for elem in arr do
puts elem
end
# note that elem is accessible outside of the for loop
elem # => 3
# good
arr.each { |elem| puts elem }
# elem is not accessible outside each's block
elem # => NameError: undefined local variable or method `elem'
Do not use then for multi-line if/unless.
[link]
# bad
if some_condition then
# body omitted
end
# good
if some_condition
# body omitted
end
Always put the condition on the same line as the if/unless in a
multi-line conditional.
[link]
# bad
if
some_condition
do_something
do_something_else
end
# good
if some_condition
do_something
do_something_else
end
Favor the ternary operator(?:) over if/then/else/end constructs.
It's more common and obviously more concise.
[link]
# bad
result = if some_condition then something else something_else end
# good
result = some_condition ? something : something_else
Use one expression per branch in a ternary operator. This
also means that ternary operators must not be nested. Prefer
if/else constructs in these cases.
[link]
# bad
some_condition ? (nested_condition ? nested_something : nested_something_else) : something_else
# good
if some_condition
nested_condition ? nested_something : nested_something_else
else
something_else
end
Do not use if x; .... Use the ternary
operator instead.
[link]
# bad
result = if some_condition; something else something_else end
# good
result = some_condition ? something : something_else
Leverage the fact that if and case are expressions which return a
result.
[link]
# bad
if condition
result = x
else
result = y
end
# good
result =
if condition
x
else
y
end
Use when x then ... for one-line cases. The alternative syntax when x: ... has been removed as of Ruby 1.9.
[link]
Do not use when x; .... See the previous rule.
[link]
Use ! instead of not.
[link]
# bad - parentheses are required because of op precedence
x = (not something)
# good
x = !something
Avoid the use of !!.
[link]
!! converts a value to boolean, but you don't need this explicit
conversion in the condition of a control expression; using it only
obscures your intention. If you want to do a nil check, use nil?
instead.
# bad
x = 'test'
# obscure nil check
if !!x
# body omitted
end
# good
x = 'test'
if x
# body omitted
end
The and and or keywords are banned. The minimal added readability is just
not worth the high probability of introducing subtle bugs. For boolean
expressions, always use && and || instead. For flow control, use
if and unless; && and || are also acceptable but less clear.
[link]
# bad
# boolean expression
ok = got_needed_arguments and arguments_are_valid
# control flow
document.save or fail(RuntimeError, "Failed to save document!")
# good
# boolean expression
ok = got_needed_arguments && arguments_are_valid
# control flow
fail(RuntimeError, "Failed to save document!") unless document.save
# ok
# control flow
document.save || fail(RuntimeError, "Failed to save document!")
Avoid multi-line ?: (the ternary operator); use if/unless instead.
[link]
Favor modifier if/unless usage when you have a single-line body. Another
good alternative is the usage of control flow &&/||.
[link]
# bad
if some_condition
do_something
end
# good
do_something if some_condition
# another good option
some_condition && do_something
Avoid modifier if/unless usage at the end of a non-trivial multi-line
block.
[link]
# bad
10.times do
# multi-line body omitted
end if some_condition
# good
if some_condition
10.times do
# multi-line body omitted
end
end
Avoid nested modifier if/unless/while/until usage. Favor &&/|| if
appropriate.
[link]
# bad
do_something if other_condition if some_condition
# good
do_something if some_condition && other_condition
Favor unless over if for negative conditions (or control flow ||).
[link]
# bad
do_something if !some_condition
# bad
do_something if not some_condition
# good
do_something unless some_condition
# another good option
some_condition || do_something
Do not use unless with else. Rewrite these with the positive case first.
[link]
# bad
unless success?
puts 'failure'
else
puts 'success'
end
# good
if success?
puts 'success'
else
puts 'failure'
end
Don't use parentheses around the condition of a control expression. [link]
# bad
if (x > 10)
# body omitted
end
# good
if x > 10
# body omitted
end
Note that there is an exception to this rule, namely safe assignment in condition.
Do not use while/until condition do for multi-line while/until.
[link]
# bad
while x > 5 do
# body omitted
end
until x > 5 do
# body omitted
end
# good
while x > 5
# body omitted
end
until x > 5
# body omitted
end
Favor modifier while/until usage when you have a single-line body.
[link]
# bad
while some_condition
do_something
end
# good
do_something while some_condition
Favor until over while for negative conditions.
[link]
# bad
do_something while !some_condition
# good
do_something until some_condition
Use Kernel#loop instead of while/until when you need an infinite loop.
[link]
# bad
while true
do_something
end
until false
do_something
end
# good
loop do
do_something
end
Use Kernel#loop with break rather than begin/end/until or
begin/end/while for post-loop tests.
[link]
# bad
begin
puts val
val += 1
end while val < 0
# good
loop do
puts val
val += 1
break unless val < 0
end
Omit the outer braces around an implicit options hash. [link]
# bad
user.set({ name: 'John', age: 45, permissions: { read: true } })
# good
user.set(name: 'John', age: 45, permissions: { read: true })
Omit both the outer braces and parentheses for methods that are part of an internal DSL. [link]
class Person < ActiveRecord::Base
# bad
validates(:name, { presence: true, length: { within: 1..10 } })
# good
validates :name, presence: true, length: { within: 1..10 }
end
Use the proc invocation shorthand when the invoked method is the only operation of a block. [link]
# bad
names.map { |name| name.upcase }
# good
names.map(&:upcase)
Prefer {...} over do...end for single-line blocks. Avoid using {...}
for multi-line blocks (multi-line chaining is always ugly), except in
RSpec source files, e.g., when using before, let, subject, etc. Always use
do...end for "control flow" and "method definitions" (e.g. in Rakefiles and
certain DSLs). Avoid do...end when chaining.
[link]
names = %w[Bozhidar Steve Sarah]
# bad
names.each do |name|
puts name
end
# good
names.each { |name| puts name }
# bad
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?
Consider using explicit block argument to avoid writing block literal that just passes its arguments to another block. Beware of the performance impact, though, as the block gets converted to a Proc. [link]
require 'tempfile'
# bad
def with_tmp_dir
Dir.mktmpdir do |tmp_dir|
Dir.chdir(tmp_dir) { |dir| yield dir } # block just passes arguments
end
end
# good
def with_tmp_dir(&block)
Dir.mktmpdir do |tmp_dir|
Dir.chdir(tmp_dir, &block)
end
end
with_tmp_dir do |dir|
puts "dir is accessible as a parameter and pwd is set: #{dir}"
end
Avoid return where not required for flow of control.
[link]
# bad
def some_method(some_arr)
return some_arr.size
end
# good
def some_method(some_arr)
some_arr.size
end
Avoid self where not required. (It is only required when calling a self
write accessor, methods named after reserved words, or overloadable operators.)
[link]
# bad
def ready?
if self.last_reviewed_at > self.last_updated_at
self.worker.update(self.content, self.options)
self.status = :in_progress
end
self.status == :verified
end
# good
def ready?
if last_reviewed_at > last_updated_at
worker.update(content, options)
self.status = :in_progress
end
status == :verified
end
As a corollary, avoid shadowing methods with local variables unless they are both equivalent. [link]
class Foo
attr_accessor :options
# ok
def initialize(options)
self.options = options
# both options and self.options are equivalent here
end
# bad
def do_something(options = {})
unless options[:when] == :later
output(self.options[:message])
end
end
# good
def do_something(params = {})
unless params[:when] == :later
output(options[:message])
end
end
end
Don't use the return value of = (an assignment) in conditional expressions
unless the assignment is wrapped in parentheses. This is a fairly popular
idiom among Rubyists that's sometimes referred to as safe assignment in
condition.
[link]
# bad (+ a warning)
if v = array.grep(/foo/)
do_something(v)
# some code
end
# good (MRI would still complain, but RuboCop won't)
if (v = array.grep(/foo/))
do_something(v)
# some code
end
# good
v = array.grep(/foo/)
if v
do_something(v)
# some code
end
Use shorthand self assignment operators whenever applicable. [link]
# bad
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
Use ||= to initialize variables only if they're not already initialized.
[link]
# bad
name = name ? name : 'Bozhidar'
# bad
name = 'Bozhidar' unless name
# good - set name to 'Bozhidar', only if it's nil or false
name ||= 'Bozhidar'
Don't use ||= to initialize boolean variables. (Consider what would happen
if the current value happened to be false.)
[link]
# bad - would set enabled to true even if it was false
enabled ||= true
# good
enabled = true if enabled.nil?
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.
[link]
# bad
if something
something = something.downcase
end
# bad
something = something ? something.downcase : nil
# ok
something = something.downcase if something
# good
something = something && something.downcase
# better
something &&= something.downcase
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.
[link]
# bad
Array === something
(1..100) === 7
/something/ === some_string
# good
something.is_a?(Array)
(1..100).include?(7)
some_string =~ /something/
Do not use eql? when using == will do. The stricter comparison semantics
provided by eql? are rarely needed in practice.
[link]
# 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
Avoid using Perl-style special variables (like $:, $;, etc. ). They are
quite cryptic and their use in anything but one-liner scripts is discouraged.
Use the human-friendly aliases provided by the English library.
[link]
# bad
$:.unshift File.dirname(__FILE__)
# good
require 'English'
$LOAD_PATH.unshift File.dirname(__FILE__)
Do not put a space between a method name and the opening parenthesis. [link]
# bad
f (3 + 2) + 1
# good
f(3 + 2) + 1
Always run the Ruby interpreter with the -w option so it will warn you if
you forget either of the rules above!
[link]
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. [link]
# bad
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
Use the new lambda literal syntax for single line body blocks. Use the
lambda method for multi-line blocks.
[link]
# bad
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
Don't omit the parameter parentheses when defining a stabby lambda with parameters. [link]
# bad
l = ->x, y { something(x, y) }
# good
l = ->(x, y) { something(x, y) }
Omit the parameter parentheses when defining a stabby lambda with no parameters. [link]
# bad
l = ->() { something }
# good
l = -> { something }
Prefer proc over Proc.new.
[link]
# bad
p = Proc.new { |n| puts n }
# good
p = proc { |n| puts n }
Prefer proc.call() over proc[] or proc.() for both lambdas and procs.
[link]
# bad - looks similar to Enumeration access
l = ->(v) { puts v }
l[1]
# also bad - uncommon syntax
l = ->(v) { puts v }
l.(1)
# good
l = ->(v) { puts v }
l.call(1)
Prefix with _ unused block parameters and local variables. It's also
acceptable to use just _ (although it's a bit less descriptive). This
convention is recognized by the Ruby interpreter and tools like RuboCop and
will suppress their unused variable warnings.
[link]
# bad
result = hash.map { |k, v| v + 1 }
def something(x)
unused_var, used_var = something_else(x)
# some code
end
# good
result = hash.map { |_k, v| v + 1 }
def something(x)
_unused_var, used_var = something_else(x)
# some code
end
# good
result = hash.map { |_, v| v + 1 }
def something(x)
_, used_var = something_else(x)
# some code
end
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.
[link]
Use warn instead of $stderr.puts. Apart from being more concise and
clear, warn allows you to suppress warnings if you need to (by setting the
warn level to 0 via -W0).
[link]
Favor the use of sprintf and its alias format over the fairly cryptic
String#% method.
[link]
# bad
'%d %d' % [20, 10]
# => '20 10'
# good
sprintf('%d %d', 20, 10)
# => '20 10'
# good
sprintf('%{first} %{second}', first: 20, second: 10)
# => '20 10'
format('%d %d', 20, 10)
# => '20 10'
# good
format('%{first} %{second}', first: 20, second: 10)
# => '20 10'
Favor the use of Array#join over the fairly cryptic Array#* with
a string argument.
[link]
# bad
%w[one two three] * ', '
# => 'one, two, three'
# good
%w[one two three].join(', ')
# => 'one, two, three'
Use Array() instead of explicit 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.
[link]
# bad
paths = [paths] unless paths.is_a? Array
paths.each { |path| do_something(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) }
Use ranges or Comparable#between? instead of complex comparison logic when
possible.
[link]
# bad
do_something if x >= 1000 && x <= 2000
# good
do_something if (1000..2000).include?(x)
# good
do_something if x.between?(1000, 2000)
Favor the use of predicate methods to explicit comparisons with ==.
Numeric comparisons are OK.
[link]
# bad
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
Don't do explicit non-nil checks unless you're dealing with boolean
values.
[link]
# bad
do_something if !something.nil?
do_something if something != nil
# good
do_something if something
# good - dealing with a boolean
def value_set?
!@some_boolean.nil?
end
Avoid the use of BEGIN blocks.
[link]
Do not use END blocks. Use Kernel#at_exit instead.
[link]
# bad
END { puts 'Goodbye!' }
# good
at_exit { puts 'Goodbye!' }
Avoid the use of flip-flops. [link]
Avoid use of nested conditionals for flow of control. [link]
Prefer a guard clause when you can assert invalid data. A guard clause is a conditional statement at the top of a function that bails out as soon as it can.
# bad
def compute_thing(thing)
if thing[:foo]
update_with_bar(thing[:foo])
if thing[:foo][:bar]
partial_compute(thing)
else
re_compute(thing)
end
end
end
# good
def compute_thing(thing)
return unless thing[:foo]
update_with_bar(thing[:foo])
return re_compute(thing) unless thing[:foo][:bar]
partial_compute(thing)
end
Prefer next in loops instead of conditional blocks.
# bad
[0, 1, 2, 3].each do |item|
if item > 1
puts item
end
end
# good
[0, 1, 2, 3].each do |item|
next unless item > 1
puts item
end
Prefer map over collect, find over detect, select over find_all,
reduce over inject 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.
[link]
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.
[link]
# bad
some_hash.count
# good
some_hash.size
Use flat_map instead of 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.
[link]
# bad
all_songs = users.map(&:songs).flatten.uniq
# good
all_songs = users.flat_map(&:songs).uniq
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.
[link]
# bad
array.reverse.each { ... }
# good
array.reverse_each { ... }
The only real difficulties in programming are cache invalidation and naming things.
-- Phil Karlton
Name identifiers in English. [link]
# bad - identifier using non-ascii characters
заплата = 1_000
# bad - identifier is a Bulgarian word, written with Latin letters (instead of Cyrillic)
zaplata = 1_000
# good
salary = 1_000
Use snake_case for symbols, methods and variables.
[link]
# bad
:'some symbol'
:SomeSymbol
:someSymbol
someVar = 5
var_10 = 10
def someMethod
# some code
end
def SomeMethod
# some code
end
# good
:some_symbol
some_var = 5
var10 = 10
def some_method
# some code
end
Do not separate numbers from letters on symbols, methods and variables. [link]
# bad
:some_sym_1
some_var_1 = 1
def some_method_1
# some code
end
# good
:some_sym1
some_var1 = 1
def some_method1
# some code
end
Use CamelCase for classes and modules. (Keep acronyms like HTTP, RFC, XML
uppercase.)
[link]
# bad
class Someclass
# some code
end
class Some_Class
# some code
end
class SomeXml
# some code
end
class XmlSomething
# some code
end
# good
class SomeClass
# some code
end
class SomeXML
# some code
end
class XMLSomething
# some code
end
Use snake_case for naming files, e.g. hello_world.rb.
[link]
Use snake_case for naming directories, e.g.
lib/hello_world/hello_world.rb.
[link]
Aim to have just a single class/module per source file. Name the file name as the class/module, but replacing CamelCase with snake_case. [link]
Use SCREAMING_SNAKE_CASE for other constants.
[link]
# bad
SomeConst = 5
# good
SOME_CONST = 5
The names of predicate methods (methods that return a boolean value) should
end in a question mark. (i.e. Array#empty?). Methods that don't return a
boolean, shouldn't end in a question mark.
[link]
Avoid prefixing predicate methods with the auxiliary verbs such as is,
does, or can. These words are redundant and inconsistent with the style of
boolean methods in the Ruby core library, such as empty? and include?.
[link]
# bad
class Person
def is_tall?
true
end
def can_play_basketball?
false
end
def does_like_candy?
true
end
end
# good
class Person
def tall?
true
end
def basketball_player?
false
end
def likes_candy?
true
end
end
The names of potentially dangerous methods (i.e. methods that modify
self or the arguments, exit! (doesn't run the finalizers like exit
does), etc.) should end with an exclamation mark if there exists a safe
version of that dangerous method.
[link]
# bad - there is no matching 'safe' method
class Person
def update!
end
end
# good
class Person
def update
end
end
# good
class Person
def update!
end
def update
end
end
Define the non-bang (safe) method in terms of the bang (dangerous) one if possible. [link]
class Array
def flatten_once!
res = []
each do |e|
[*e].each { |f| res << f }
end
replace(res)
end
def flatten_once
dup.flatten_once!
end
end
When defining binary operators, name the parameter other(<< and [] are
exceptions to the rule, since their semantics are different).
[link]
def +(other)
# body omitted
end
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.
-- Steve McConnell
Write self-documenting code and ignore the rest of this section. Seriously! [link]
Write comments in English. [link]
Use one space between the leading # character of the comment and the text
of the comment.
[link]
Comments longer than a word are capitalized and use punctuation. Use one space after periods. [link]
Avoid superfluous comments. [link]
# bad
counter += 1 # Increments counter by one.
Keep existing comments up-to-date. An outdated comment is worse than no comment at all. [link]
Good code is like a good joke: it needs no explanation.
— old programmers maxim, through Russ Olsen
Annotations should usually be written on the line immediately above the relevant code. [link]
The annotation keyword is followed by a colon and a space, then a note describing the problem. [link]
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).
[link]
def bar
# FIXME: This has crashed occasionally since v3.2.1. It may
# be related to the BarBazUtil upgrade.
baz(:quux)
end
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. [link]
def bar
sleep 100 # OPTIMIZE
end
Use TODO to note missing features or functionality that should be added at
a later date.
[link]
Use FIXME to note broken code that needs to be fixed.
[link]
Use OPTIMIZE to note slow or inefficient code that may cause performance
problems.
[link]
Use HACK to note code smells where questionable coding practices were used
and should be refactored away.
[link]
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?
[link]
Use other custom annotation keywords if it feels appropriate, but be sure to
document them in your project's README or similar.
[link]
Place magic comments above all code and documentation. Magic comments should only go below shebangs if they are needed in your source file. [link]
# good
# frozen_string_literal: true
# Some documentation about Person
class Person
end
# bad
# Some documentation about Person
# frozen_string_literal: true
class Person
end
# good
#!/usr/bin/env ruby
# frozen_string_literal: true
App.parse(ARGV)
# bad
# frozen_string_literal: true
#!/usr/bin/env ruby
App.parse(ARGV)
Use one magic comment per line if you need multiple. [link]
# good
# frozen_string_literal: true
# encoding: ascii-8bit
# bad
# -*- frozen_string_literal: true; encoding: ascii-8bit -*-
Separate magic comments from code and documentation with a blank line. [link]
# good
# frozen_string_literal: true
# Some documentation for Person
class Person
# Some code
end
# bad
# frozen_string_literal: true
# Some documentation for Person
class Person
# Some code
end
Use a consistent structure in your class definitions. [link]
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 some_protected_method
end
private
def some_private_method
end
end
Split multiple mixins into separate statements. [link]
# bad
class Person
include Foo, Bar
end
# good
class Person
# multiple mixins go in separate statements
include Foo
include Bar
end
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. [link]
# bad
# foo.rb
class Foo
class Bar
# 30 methods inside
end
class Car
# 20 methods inside
end
# 30 methods inside
end
# good
# 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
Prefer modules to classes with only class methods. Classes should be used only when it makes sense to create instances out of them. [link]
# bad
class SomeClass
def self.some_method
# body omitted
end
def self.some_other_method
# body omitted
end
end
# good
module SomeModule
module_function
def some_method
# body omitted
end
def some_other_method
# body omitted
end
end
Favor the use of module_function over extend self when you want to turn
a module's instance methods into class methods.
[link]
# bad
module Utilities
extend self
def parse_something(string)
# do stuff here
end
def other_utility_method(number, string)
# do some more stuff
end
end
# good
module Utilities
module_function
def parse_something(string)
# do stuff here
end
def other_utility_method(number, string)
# do some more stuff
end
end
When designing class hierarchies make sure that they conform to the Liskov Substitution Principle. [link]
Always supply a proper to_s method for classes that represent domain
objects.
[link]
class Person
attr_reader :first_name, :last_name
def initialize(first_name, last_name)
@first_name = first_name
@last_name = last_name
end
def to_s
"#{@first_name} #{@last_name}"
end
end
Use the attr family of functions to define trivial accessors or mutators.
[link]
# bad
class Person
def initialize(first_name, last_name)
@first_name = first_name
@last_name = last_name
end
def first_name
@first_name
end
def last_name
@last_name
end
end
# good
class Person
attr_reader :first_name, :last_name
def initialize(first_name, last_name)
@first_name = first_name
@last_name = last_name
end
end
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).
[link]
# bad
class Person
def get_name
"#{@first_name} #{@last_name}"
end
def set_name(name)
@first_name, @last_name = name.split(' ')
end
end
# good
class Person
def name
"#{@first_name} #{@last_name}"
end
def name=(name)
@first_name, @last_name = name.split(' ')
end
end
Avoid the use of attr. Use attr_reader and attr_accessor instead.
[link]
# 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
attr_reader :one, :two, :three
Consider using Struct.new, which defines the trivial accessors,
constructor and comparison operators for you.
[link]
# good
class Person
attr_accessor :first_name, :last_name
def initialize(first_name, last_name)
@first_name = first_name
@last_name = last_name
end
end
# better
Person = Struct.new(:first_name, :last_name) do
end
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.
[link]
# bad
class Person < Struct.new(:first_name, :last_name)
end
# good
Person = Struct.new(:first_name, :last_name)
Consider adding factory methods to provide additional sensible ways to create instances of a particular class. [link]
class Person
def self.create(options_hash)
# body omitted
end
end
Prefer duck-typing over inheritance. [link]
# bad
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
Avoid the usage of class (@@) variables due to their "nasty" behavior in
inheritance.
[link]
class Parent
@@class_var = 'parent'
def self.print_class_var
puts @@class_var
end
end
class Child < Parent
@@class_var = 'child'
end
Parent.print_class_var # => 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.
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.
[link]
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.
[link]
class SomeClass
def public_method
# some code
end
private
def private_method
# some code
end
def another_private_method
# some code
end
end
Use def self.method to define class methods. This makes the code
easier to refactor since the class name is not repeated.
[link]
class TestClass
# bad
def TestClass.some_method
# body omitted
end
# good
def self.some_other_method
# 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
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.
[link]
class Westerner
def first_name
@names.first
end
alias given_name first_name
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.
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.
class Fugitive < Westerner
def first_name
'Nobody'
end
alias given_name first_name
end
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.
[link]
module Mononymous
def self.included(other)
other.class_eval { alias_method :full_name, :given_name }
end
end
class Sting < Westerner
include Mononymous
end
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.
[link]
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
Prefer raise over fail for exceptions.
[link]
# bad
fail SomeException, 'message'
# good
raise SomeException, 'message'
Don't specify RuntimeError explicitly in the two argument version of
raise.
[link]
# bad
raise RuntimeError, 'message'
# good - signals a RuntimeError by default
raise 'message'
Prefer supplying an exception class and a message as two separate arguments
to raise, instead of an exception instance.
[link]
# bad
raise SomeException.new('message')
# Note that there is no way to do `raise SomeException.new('message'), backtrace`.
# good
raise SomeException, 'message'
# Consistent with `raise SomeException, 'message', backtrace`.
Do not return from an ensure block. If you explicitly return from a method
inside an ensure block, the return will take precedence over any exception
being raised, and the method will return as if no exception had been raised at
all. In effect, the exception will be silently thrown away.
[link]
# bad
def foo
raise
ensure
return 'very bad idea'
end
Use implicit begin blocks where possible. [link]
# bad
def foo
begin
# main logic goes here
rescue
# failure handling goes here
end
end
# good
def foo
# main logic goes here
rescue
# failure handling goes here
end
Mitigate the proliferation of begin blocks by using contingency methods
(a term coined by Avdi Grimm).
[link]
# bad
begin
something_that_might_fail
rescue IOError
# handle IOError
end
begin
something_else_that_might_fail
rescue IOError
# handle IOError
end
# good
def with_io_error_handling
yield
rescue IOError
# handle IOError
end
with_io_error_handling { something_that_might_fail }
with_io_error_handling { something_else_that_might_fail }
Don't suppress exceptions. [link]
# bad
begin
# an exception occurs here
rescue SomeError
# the rescue clause does absolutely nothing
end
# bad
do_something rescue nil
Avoid using rescue in its modifier form.
[link]
# bad - this catches exceptions of StandardError class and its descendant classes
read_file rescue handle_error($!)
# good - this catches only the exceptions of Errno::ENOENT class and its descendant classes
def foo
read_file
rescue Errno::ENOENT => ex
handle_error(ex)
end
Don't use exceptions for flow of control. [link]
# bad
begin
n / d
rescue ZeroDivisionError
puts 'Cannot divide by 0!'
end
# good
if d.zero?
puts 'Cannot divide by 0!'
else
n / d
end
Avoid rescuing the Exception class. This will trap signals and calls to
exit, requiring you to kill -9 the process.
[link]
# bad
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
Put more specific exceptions higher up the rescue chain, otherwise they'll never be rescued from. [link]
# bad
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 obtained by your program in an ensure block.
[link]
f = File.open('testfile')
begin
# .. process
rescue
# .. handle error
ensure
f.close if f
end
Use versions of resource obtaining methods that do automatic resource cleanup when possible. [link]
# bad - you need to close the file descriptor explicitly
f = File.open('testfile')
# some action on the file
f.close
# good - the file descriptor is closed automatically
File.open('testfile') do |f|
# some action on the file
end
Favor the use of exceptions from the standard library over introducing new exception classes. [link]
Prefer literal array and hash creation notation (unless you need to pass parameters to their constructors, that is). [link]
# bad
arr = Array.new
hash = Hash.new
# good
arr = []
hash = {}
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.
[link]
# bad
STATES = ['draft', 'open', 'closed']
# good
STATES = %w[draft open closed]
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.
[link]
# bad
STATES = [:draft, :open, :closed]
# good
STATES = %i[draft open closed]
Avoid comma after the last item of an Array or Hash literal, especially
when the items are not on separate lines.
[link]
# bad - easier to move/add/remove items, but still not preferred
VALUES = [
1001,
2020,
3333,
]
# bad
VALUES = [1001, 2020, 3333, ]
# good
VALUES = [1001, 2020, 3333]
Avoid the creation of huge gaps in arrays. [link]
arr = []
arr[100] = 1 # now you have an array with lots of nils
When accessing the first or last element from an array, prefer first or
last over [0] or [-1].
[link]
Use Set instead of 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.
[link]
Prefer symbols instead of strings as hash keys. [link]
# bad
hash = { 'one' => 1, 'two' => 2, 'three' => 3 }
# good
hash = { one: 1, two: 2, three: 3 }
Avoid the use of mutable objects as hash keys. [link]
Use the Ruby 1.9 hash literal syntax when your hash keys are symbols. [link]
# bad
hash = { :one => 1, :two => 2, :three => 3 }
# good
hash = { one: 1, two: 2, three: 3 }
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. [link]
# bad
{ a: 1, 'b' => 2 }
# good
{ :a => 1, 'b' => 2 }
Use Hash#key? instead of Hash#has_key? and Hash#value? instead of
Hash#has_value?.
[link]
# bad
hash.has_key?(:test)
hash.has_value?(value)
# good
hash.key?(:test)
hash.value?(value)
Use Hash#each_key instead of Hash#keys.each and Hash#each_value
instead of Hash#values.each.
[link]
# bad
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 }
Use Hash#fetch when dealing with hash keys that should be present.
[link]
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)
Introduce default values for hash keys via Hash#fetch as opposed to using
custom logic.
[link]
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 work correctly with falsy values
batman.fetch(:is_evil, true) # => false
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.
[link]
batman = { name: 'Bruce Wayne' }
# bad - if we use the default value, we eager evaluate it
# so it can slow the program down if done multiple times
batman.fetch(:powers, obtain_batman_powers) # obtain_batman_powers is an expensive call
# good - blocks are lazy evaluated, so only triggered in case of KeyError exception
batman.fetch(:powers) { obtain_batman_powers }
Use Hash#values_at when you need to retrieve several values consecutively
from a hash.
[link]
# bad
email = data['email']
username = data['nickname']
# good
email, username = data.values_at('email', 'nickname')
Rely on the fact that as of Ruby 1.9 hashes are ordered. [link]
Do not modify a collection while traversing it. [link]
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.
[link]
# bad
Regexp.last_match[1]
# good
Regexp.last_match(1)
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.
[link]
# bad
def awesome_things
@awesome_things
end
# good
def awesome_things(index = nil)
if index && @awesome_things
@awesome_things[index]
else
@awesome_things
end
end
Use Integer 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.
[link]
timestamp = Time.now.to_i
# bad
timestamp.is_a? Fixnum
timestamp.is_a? Bignum
# good
timestamp.is_a? Integer
Prefer to use ranges when generating random numbers instead of integers with offsets, since it clearly states your intentions. Imagine simulating a role of a dice: [link]
# bad
rand(6) + 1
# good
rand(1..6)
Prefer string interpolation and string formatting instead of string concatenation: [link]
# bad
email_with_name = user.name + ' <' + user.email + '>'
# good
email_with_name = "#{user.name} <#{user.email}>"
# good
email_with_name = format('%s <%s>', user.name, user.email)
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 (Option A) and double quotes by default (Option B). [link]
(Option A) Prefer single-quoted strings when you don't need
string interpolation or special symbols such as \t, \n, ',
etc.
# bad
name = "Bozhidar"
# good
name = 'Bozhidar'
(Option B) Prefer double-quotes unless your string literal
contains " or escape characters you want to suppress.
# bad
name = 'Bozhidar'
# good
name = "Bozhidar"
The string literals in this guide are aligned with the first style.
Don't use the character literal syntax ?x. Since Ruby 1.9 it's basically
redundant—?x would interpreted as 'x' (a string with a single
character in it).
[link]
# bad
char = ?c
# good
char = 'c'
Don't leave out {} around instance and global variables being interpolated
into a string.
[link]
class Person
attr_reader :first_name, :last_name
def initialize(first_name, last_name)
@first_name = first_name
@last_name = last_name
end
# bad - valid, but awkward
def to_s
"#@first_name #@last_name"
end
# good
def to_s
"#{@first_name} #{@last_name}"
end
end
$global = 0
# bad
puts "$global = #$global"
# good
puts "$global = #{$global}"
Don't use Object#to_s on interpolated objects. It's invoked on them
automatically.
[link]
# bad
message = "This is the #{result.to_s}."
# good
message = "This is the #{result}."
Avoid using String#+ when you need to construct large data chunks.
Instead, use String#<<. Concatenation mutates the string instance in-place
and is always faster than String#+, which creates a bunch of new string
objects.
[link]
# bad
html = ''
html += '<h1>Page title</h1>'
paragraphs.each do |paragraph|
html += "<p>#{paragraph}</p>"
end
# good and also fast
html = ''
html << '<h1>Page title</h1>'
paragraphs.each do |paragraph|
html << "<p>#{paragraph}</p>"
end
Don't use String#gsub in scenarios in which you can use a faster more specialized alternative.
[link]
url = 'http://example.com'
str = 'lisp-case-rules'
# bad
url.gsub('http://', 'https://')
str.gsub('-', '_')
# good
url.sub('http://', 'https://')
str.tr('-', '_')
When using heredocs for multi-line strings keep in mind the fact that they preserve leading whitespace. It's a good practice to employ some margin based on which to trim the excessive whitespace. [link]
code = <<-END.gsub(/^\s+\|/, '')
|def test
| some_method
| other_method
|end
END
# => "def test\n some_method\n other_method\nend\n"
Use Ruby 2.3's squiggly heredocs for nicely indented multi-line strings. [link]
# bad - using Powerpack String#strip_margin
code = <<-END.strip_margin('|')
|def test
| some_method
| other_method
|end
END
# also bad
code = <<-END
def test
some_method
other_method
end
END
# good
code = <<~END
def test
some_method
other_method
end
END
Prefer Time.now over Time.new when retrieving the current system time.
[link]
Don't use DateTime unless you need to account for historical calendar
reform -- and if you do, explicitly specify the start argument to
clearly state your intentions.
[link]
# bad - uses DateTime for current time
DateTime.now
# good - uses Time for current time
Time.now
# bad - uses DateTime for modern date
DateTime.iso8601('2016-06-29')
# good - uses Date for modern date
Date.iso8601('2016-06-29')
# good - uses DateTime with start argument for historical date
DateTime.iso8601('1751-04-23', Date::ENGLAND)
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.
-- Jamie Zawinski
Don't use regular expressions if you just need plain text search in string:
string['text']
[link]
For simple constructions you can use regexp directly through string index. [link]
match = string[/regexp/] # get content of matched regexp
first_group = string[/text(grp)/, 1] # get content of captured group
string[/text (grp)/, 1] = 'replace' # string => 'text replace'
Use non-capturing groups when you don't use the captured result. [link]
# bad
/(first|second)/
# good
/(?:first|second)/
Don't use the cryptic Perl-legacy variables denoting last regexp group
matches ($1, $2, etc). Use Regexp.last_match(n) instead.
[link]
/(regexp)/ =~ string
...
# bad
process $1
# good
process Regexp.last_match(1)
Avoid using numbered groups as it can be hard to track what they contain. Named groups can be used instead. [link]
# bad
/(regexp)/ =~ string
# some code
process Regexp.last_match(1)
# good
/(?<meaningful_var>regexp)/ =~ string
# some code
process meaningful_var
Character classes have only a few special characters you should care about:
^, -, \, ], so don't escape . or brackets in [].
[link]
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/).
[link]
string = "some injection\nusername"
string[/^username$/] # matches
string[/\Ausername\z/] # doesn't match
Use x modifier for complex regexps. This makes them more readable and you
can add some useful comments. Just be careful as spaces are ignored.
[link]
regexp = /
start # some text
\s # white space char
(group) # first group
(?:alt1|alt2) # some alternation
end
/x
For complex replacements sub/gsub can be used with a block or a hash.
[link]
words = 'foo bar'
words.sub(/f/, 'f' => 'F') # => 'Foo bar'
words.gsub(/\w+/) { |word| word.capitalize } # => 'Foo Bar'
Use %()(it's a shorthand for %Q) for single-line strings which require
both interpolation and embedded double-quotes. For multi-line strings, prefer
heredocs.
[link]
# bad (no interpolation needed)
%(<div class="text">Some text</div>)
# should be '<div class="text">Some text</div>'
# bad (no double-quotes)
%(This is #{quality} style)
# should be "This is #{quality} style"
# bad (multiple lines)
%(<div>\n<span class="big">#{exclamation}</span>\n</div>)
# should be a heredoc.
# good (requires interpolation, has quotes, single line)
%(<tr><td class="name">#{name}</td>)
Avoid %() or the equivalent %q() unless you have a string with both ' and
" in it. Regular string literals are more readable and should be preferred
unless a lot of characters would have to be escaped in them.
[link]
# bad
name = %q(Bruce Wayne)
time = %q(8 o'clock)
question = %q("What did you say?")
# good
name = 'Bruce Wayne'
time = "8 o'clock"
question = '"What did you say?"'
quote = %q(<p class='quote'>"What did you say?"</p>)
Use %r only for regular expressions matching at least one '/'
character.
[link]
# bad
%r{\s+}
# good
%r{^/(.*)$}
%r{^/blog/2011/(.*)$}
Avoid the use of %x unless you're going to invoke a command with
backquotes in it(which is rather unlikely).
[link]
# bad
date = %x(date)
# good
date = `date`
echo = %x(echo `date`)
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.
[link]
Use the braces that are the most appropriate for the various kinds of percent literals. [link]
() 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)# bad
%q{"Test's king!", John said.}
# good
%q("Test's king!", John said.)
# bad
%w(one two three)
%i(one two three)
# good
%w[one two three]
%i[one two three]
# bad
%r((\w+)-(\d+))
%r{\w{1,2}\d{2,5}}
# good
%r{(\w+)-(\d+)}
%r|\w{1,2}\d{2,5}|
Avoid needless metaprogramming. [link]
Do not mess around in core classes when writing libraries. (Do not monkey-patch them.) [link]
The block form of class_eval is preferable to the string-interpolated
form.
[link]
when you use the string-interpolated form, always supply __FILE__
and __LINE__, so that your backtraces make sense:
class_eval 'def use_relative_model_naming?; true; end', __FILE__, __LINE__
define_method is preferable to class_eval{ def ... }
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):
[link]
# from activesupport/lib/active_support/core_ext/string/output_safety.rb
UNSAFE_STRING_METHODS.each do |unsafe_method|
if 'String'.respond_to?(unsafe_method)
class_eval <<-EOT, __FILE__, __LINE__ + 1
def #{unsafe_method}(*params, &block) # def capitalize(*params, &block)
to_str.#{unsafe_method}(*params, &block) # to_str.capitalize(*params, &block)
end # end
def #{unsafe_method}!(*params) # def capitalize!(*params)
@dirty = true # @dirty = true
super # super
end # end
EOT
end
end
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.launch_state = false. Consider using
delegation, proxy, or define_method instead. If you must use
method_missing:
[link]
Be sure to 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:
# bad
def method_missing?(meth, *params, &block)
if /^find_by_(?<prop>.*)/ =~ meth
# ... lots of code to do a find_by
else
super
end
end
# good
def method_missing?(meth, *params, &block)
if /^find_by_(?<prop>.*)/ =~ meth
find_by(prop, *params, &block)
else
super
end
end
# best of all, though, would to define_method as each findable attribute is declared
Prefer public_send over send so as not to circumvent private/protected visibility.
[link]
# We have an ActiveModel Organization that includes concern Activatable
module Activatable
extend ActiveSupport::Concern
included do
before_create :create_token
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(...)
# BAD - violates privacy
linux_organization.send(:reset_token)
# GOOD - should throw an exception
linux_organization.public_send(:reset_token)
Prefer __send__ over send, as send may overlap with existing methods.
[link]
require 'socket'
u1 = UDPSocket.new
u1.bind('127.0.0.1', 4913)
u2 = UDPSocket.new
u2.connect('127.0.0.1', 4913)
# Won't send a message to the receiver obj.
# Instead it will send a message via UDP socket.
u2.send :sleep, 0
# Will actually send a message to the receiver obj.
u2.__send__ ...
Write ruby -w safe code.
[link]
Avoid hashes as optional parameters. Does the method do too much? (Object initializers are exceptions for this rule). [link]
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. [link]
Avoid parameter lists longer than three or four parameters. [link]
If you really need "global" methods, add them to Kernel and make them private. [link]
Use module instance variables instead of global variables. [link]
# bad
$foo_bar = 1
# good
module Foo
class << self
attr_accessor :bar
end
end
Foo.bar = 1
Use OptionParser for parsing complex command line options and ruby -s
for trivial command line options.
[link]
Code in a functional way, avoiding mutation when that makes sense. [link]
Do not mutate parameters unless that is the purpose of the method. [link]
Avoid more than three levels of block nesting. [link]
Be consistent. In an ideal world, be consistent with these guidelines. [link]
Use common sense. [link]
You can financially support bbatsov's original style guide (and RuboCop) with contributions via Gratipay.
It's easy, just follow the contribution guidelines.
This work is licensed under a Creative Commons Attribution 3.0 Unported License. This is a fork of the original work, with some changes.
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