cops_style.md

Style

Style/AccessModifierDeclarations

Enabled by default	Supports autocorrection
Enabled	No

Access modifiers should be declared to apply to a group of methods or inline before each method, depending on configuration.

Examples

EnforcedStyle: group (default)

# bad

class Foo

  private def bar; end
  private def baz; end

end

# good

class Foo

  private

  def bar; end
  def baz; end

end

EnforcedStyle: inline

# bad

class Foo

  private

  def bar; end
  def baz; end

end

# good

class Foo

  private def bar; end
  private def baz; end

end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	group	inline, group

Style/Alias

Enabled by default	Supports autocorrection
Enabled	Yes

This cop enforces the use of either #alias or #alias_method depending on configuration. It also flags uses of alias :symbol rather than alias bareword.

Examples

EnforcedStyle: prefer_alias (default)

# bad
alias_method :bar, :foo
alias :bar :foo

# good
alias bar foo

EnforcedStyle: prefer_alias_method

# bad
alias :bar :foo
alias bar foo

# good
alias_method :bar, :foo

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	prefer_alias	prefer_alias, prefer_alias_method

References

• https://github.com/rubocop-hq/ruby-style-guide#alias-method

Style/AndOr

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for uses of and and or, and suggests using && and || instead. It can be configured to check only in conditions, or in all contexts.

Examples

EnforcedStyle: always (default)

# bad
foo.save and return

# bad
if foo and bar
end

# good
foo.save && return

# good
if foo && bar
end

EnforcedStyle: conditionals

# bad
if foo and bar
end

# good
foo.save && return

# good
foo.save and return

# good
if foo && bar
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	always	always, conditionals

References

• https://github.com/rubocop-hq/ruby-style-guide#no-and-or-or

Style/ArrayJoin

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for uses of "*" as a substitute for join.

Not all cases can reliably checked, due to Ruby's dynamic types, so we consider only cases when the first argument is an array literal or the second is a string literal.

Examples

# bad
%w(foo bar baz) * ","

# good
%w(foo bar baz).join(",")

References

• https://github.com/rubocop-hq/ruby-style-guide#array-join

Style/AsciiComments

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for non-ascii (non-English) characters in comments. You could set an array of allowed non-ascii chars in AllowedChars attribute (empty by default).

Examples

# bad
# Translates from English to 日本語。

# good
# Translates from English to Japanese

Configurable attributes

Name	Default value	Configurable values
AllowedChars	[]	Array

References

• https://github.com/rubocop-hq/ruby-style-guide#english-comments

Style/Attr

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for uses of Module#attr.

Examples

# 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

References

• https://github.com/rubocop-hq/ruby-style-guide#attr

Style/AutoResourceCleanup

Enabled by default	Supports autocorrection
Disabled	No

This cop checks for cases when you could use a block accepting version of a method that does automatic resource cleanup.

Examples

# bad
f = File.open('file')

# good
File.open('file') do |f|
  # ...
end

Style/BarePercentLiterals

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks if usage of %() or %Q() matches configuration.

Examples

EnforcedStyle: bare_percent (default)

# bad
%Q(He said: "#{greeting}")
%q{She said: 'Hi'}

# good
%(He said: "#{greeting}")
%{She said: 'Hi'}

EnforcedStyle: percent_q

# bad
%|He said: "#{greeting}"|
%/She said: 'Hi'/

# good
%Q|He said: "#{greeting}"|
%q/She said: 'Hi'/

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	bare_percent	percent_q, bare_percent

References

• https://github.com/rubocop-hq/ruby-style-guide#percent-q-shorthand

Style/BeginBlock

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for BEGIN blocks.

References

• https://github.com/rubocop-hq/ruby-style-guide#no-BEGIN-blocks

Style/BlockComments

Enabled by default	Supports autocorrection
Enabled	Yes

This cop looks for uses of block comments (=begin...=end).

Examples

# bad
=begin
Multiple lines
of comments...
=end

# good
# Multiple lines
# of comments...

References

• https://github.com/rubocop-hq/ruby-style-guide#no-block-comments

Style/BlockDelimiters

Enabled by default	Supports autocorrection
Enabled	Yes

Check for uses of braces or do/end around single line or multi-line blocks.

Examples

EnforcedStyle: line_count_based (default)

# bad - single line block
items.each do |item| item / 5 end

# good - single line block
items.each { |item| item / 5 }

# bad - multi-line block
things.map { |thing|
  something = thing.some_method
  process(something)
}

# good - multi-line block
things.map do |thing|
  something = thing.some_method
  process(something)
end

EnforcedStyle: semantic

# Prefer `do...end` over `{...}` for procedural blocks.

# return value is used/assigned
# bad
foo = map do |x|
  x
end
puts (map do |x|
  x
end)

# return value is not used out of scope
# good
map do |x|
  x
end

# Prefer `{...}` over `do...end` for functional blocks.

# return value is not used out of scope
# bad
each { |x|
  x
}

# return value is used/assigned
# good
foo = map { |x|
  x
}
map { |x|
  x
}.inspect

EnforcedStyle: braces_for_chaining

# bad
words.each do |word|
  word.flip.flop
end.join("-")

# good
words.each { |word|
  word.flip.flop
}.join("-")

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	line_count_based	line_count_based, semantic, braces_for_chaining
ProceduralMethods	benchmark, bm, bmbm, create, each_with_object, measure, new, realtime, tap, with_object	Array
FunctionalMethods	let, let!, subject, watch	Array
IgnoredMethods	lambda, proc, it	Array

References

• https://github.com/rubocop-hq/ruby-style-guide#single-line-blocks

Style/BracesAroundHashParameters

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for braces around the last parameter in a method call if the last parameter is a hash. It supports braces, no_braces and context_dependent styles.

Examples

EnforcedStyle: braces

# The `braces` style enforces braces around all method
# parameters that are hashes.

# bad
some_method(x, y, a: 1, b: 2)

# good
some_method(x, y, {a: 1, b: 2})

EnforcedStyle: no_braces (default)

# The `no_braces` style checks that the last parameter doesn't
# have braces around it.

# bad
some_method(x, y, {a: 1, b: 2})

# good
some_method(x, y, a: 1, b: 2)

EnforcedStyle: context_dependent

# The `context_dependent` style checks that the last parameter
# doesn't have braces around it, but requires braces if the
# second to last parameter is also a hash literal.

# bad
some_method(x, y, {a: 1, b: 2})
some_method(x, y, {a: 1, b: 2}, a: 1, b: 2)

# good
some_method(x, y, a: 1, b: 2)
some_method(x, y, {a: 1, b: 2}, {a: 1, b: 2})

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	no_braces	braces, no_braces, context_dependent

Style/CaseEquality

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for uses of the case equality operator(===).

Examples

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

# good
something.is_a?(Array)
(1..100).include?(7)
some_string =~ /something/

References

• https://github.com/rubocop-hq/ruby-style-guide#no-case-equality

Style/CharacterLiteral

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for uses of the character literal ?x.

Examples

# bad
?x

# good
'x'

# good
?\C-\M-d

References

• https://github.com/rubocop-hq/ruby-style-guide#no-character-literals

Style/ClassAndModuleChildren

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks the style of children definitions at classes and modules. Basically there are two different styles:

The compact style is only forced for classes/modules with one child.

Examples

EnforcedStyle: nested (default)

# good
# have each child on its own line
class Foo
  class Bar
  end
end

EnforcedStyle: compact

# good
# combine definitions as much as possible
class Foo::Bar
end

Configurable attributes

Name	Default value	Configurable values
AutoCorrect	false	Boolean
EnforcedStyle	nested	nested, compact

References

• https://github.com/rubocop-hq/ruby-style-guide#namespace-definition

Style/ClassCheck

Enabled by default	Supports autocorrection
Enabled	Yes

This cop enforces consistent use of Object#is_a? or Object#kind_of?.

Examples

EnforcedStyle: is_a? (default)

# bad
var.kind_of?(Date)
var.kind_of?(Integer)

# good
var.is_a?(Date)
var.is_a?(Integer)

EnforcedStyle: kind_of?

# bad
var.is_a?(Time)
var.is_a?(String)

# good
var.kind_of?(Time)
var.kind_of?(String)

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	is_a?	is_a?, kind_of?

Style/ClassMethods

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for uses of the class/module name instead of self, when defining class/module methods.

Examples

# bad
class SomeClass
  def SomeClass.class_method
    # ...
  end
end

# good
class SomeClass
  def self.class_method
    # ...
  end
end

References

• https://github.com/rubocop-hq/ruby-style-guide#def-self-class-methods

Style/ClassVars

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for uses of class variables. Offenses are signaled only on assignment to class variables to reduce the number of offenses that would be reported.

You have to be careful when setting a value for a class variable; if a class has been inherited, changing the value of a class variable also affects the inheriting classes. This means that it's almost always better to use a class instance variable instead.

Examples

# bad
class A
  @@test = 10
end

# good
class A
  @test = 10
end

class A
  def test
    @@test # you can access class variable without offense
  end
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-class-vars

Style/CollectionMethods

Enabled by default	Supports autocorrection
Disabled	Yes

This cop enforces the use of consistent method names from the Enumerable module.

Unfortunately we cannot actually know if a method is from Enumerable or not (static analysis limitation), so this cop can yield some false positives.

Configurable attributes

Name	Default value	Configurable values
PreferredMethods	{"collect"=>"map", "collect!"=>"map!", "inject"=>"reduce", "detect"=>"find", "find_all"=>"select"}

References

• https://github.com/rubocop-hq/ruby-style-guide#map-find-select-reduce-size

Style/ColonMethodCall

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for methods invoked via the :: operator instead of the . operator (like FileUtils::rmdir instead of FileUtils.rmdir).

Examples

# bad
Timeout::timeout(500) { do_something }
FileUtils::rmdir(dir)
Marshal::dump(obj)

# good
Timeout.timeout(500) { do_something }
FileUtils.rmdir(dir)
Marshal.dump(obj)

References

• https://github.com/rubocop-hq/ruby-style-guide#double-colons

Style/ColonMethodDefinition

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for class methods that are defined using the :: operator instead of the . operator.

Examples

# bad
class Foo
  def self::bar
  end
end

# good
class Foo
  def self.bar
  end
end

References

• https://github.com/rubocop-hq/ruby-style-guide#colon-method-definition

Style/CommandLiteral

Enabled by default	Supports autocorrection
Enabled	Yes

This cop enforces using `` or %x around command literals.

Examples

EnforcedStyle: backticks (default)

# bad
folders = %x(find . -type d).split

# bad
%x(
  ln -s foo.example.yml foo.example
  ln -s bar.example.yml bar.example
)

# good
folders = `find . -type d`.split

# good
`
  ln -s foo.example.yml foo.example
  ln -s bar.example.yml bar.example
`

EnforcedStyle: mixed

# bad
folders = %x(find . -type d).split

# bad
`
  ln -s foo.example.yml foo.example
  ln -s bar.example.yml bar.example
`

# good
folders = `find . -type d`.split

# good
%x(
  ln -s foo.example.yml foo.example
  ln -s bar.example.yml bar.example
)

EnforcedStyle: percent_x

# bad
folders = `find . -type d`.split

# bad
`
  ln -s foo.example.yml foo.example
  ln -s bar.example.yml bar.example
`

# good
folders = %x(find . -type d).split

# good
%x(
  ln -s foo.example.yml foo.example
  ln -s bar.example.yml bar.example
)

AllowInnerBackticks: false (default)

# If `false`, the cop will always recommend using `%x` if one or more
# backticks are found in the command string.

# bad
`echo \`ls\``

# good
%x(echo `ls`)

AllowInnerBackticks: true

# good
`echo \`ls\``

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	backticks	backticks, percent_x, mixed
AllowInnerBackticks	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#percent-x

Style/CommentAnnotation

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks that comment annotation keywords are written according to guidelines.

Examples

# bad
# TODO make better

# good
# TODO: make better

# bad
# TODO:make better

# good
# TODO: make better

# bad
# fixme: does not work

# good
# FIXME: does not work

# bad
# Optimize does not work

# good
# OPTIMIZE: does not work

Configurable attributes

Name	Default value	Configurable values
Keywords	TODO, FIXME, OPTIMIZE, HACK, REVIEW	Array

References

• https://github.com/rubocop-hq/ruby-style-guide#annotate-keywords

Style/CommentedKeyword

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for comments put on the same line as some keywords. These keywords are: begin, class, def, end, module.

Note that some comments (such as :nodoc: and rubocop:disable) are allowed.

Examples

# bad
if condition
  statement
end # end if

# bad
class X # comment
  statement
end

# bad
def x; end # comment

# good
if condition
  statement
end

# good
class X # :nodoc:
  y
end

Style/ConditionalAssignment

Enabled by default	Supports autocorrection
Enabled	Yes

Check for if and case statements where each branch is used for assignment to the same variable when using the return of the condition can be used instead.

Examples

EnforcedStyle: assign_to_condition (default)

# bad
if foo
  bar = 1
else
  bar = 2
end

case foo
when 'a'
  bar += 1
else
  bar += 2
end

if foo
  some_method
  bar = 1
else
  some_other_method
  bar = 2
end

# good
bar = if foo
        1
      else
        2
      end

bar += case foo
       when 'a'
         1
       else
         2
       end

bar << if foo
         some_method
         1
       else
         some_other_method
         2
       end

EnforcedStyle: assign_inside_condition

# bad
bar = if foo
        1
      else
        2
      end

bar += case foo
       when 'a'
         1
       else
         2
       end

bar << if foo
         some_method
         1
       else
         some_other_method
         2
       end

# good
if foo
  bar = 1
else
  bar = 2
end

case foo
when 'a'
  bar += 1
else
  bar += 2
end

if foo
  some_method
  bar = 1
else
  some_other_method
  bar = 2
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	assign_to_condition	assign_to_condition, assign_inside_condition
SingleLineConditionsOnly	true	Boolean
IncludeTernaryExpressions	true	Boolean

Style/Copyright

Enabled by default	Supports autocorrection
Disabled	Yes

Check that a copyright notice was given in each source file.

The default regexp for an acceptable copyright notice can be found in config/default.yml. The default can be changed as follows:

Style/Copyright:
  Notice: '^Copyright (\(c\) )?2\d{3} Acme Inc'

This regex string is treated as an unanchored regex. For each file that RuboCop scans, a comment that matches this regex must be found or an offense is reported.

Configurable attributes

Name	Default value	Configurable values
Notice	^Copyright (\(c\) )?2[0-9]{3} .+	String
AutocorrectNotice	``	String

Style/DateTime

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for uses of DateTime that should be replaced by Date or Time.

Examples

# 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)

AllowCoercion: false (default)

# bad - coerces to `DateTime`
something.to_datetime

# good - coerces to `Time`
something.to_time

AllowCoercion: true

# good
something.to_datetime

# good
something.to_time

Configurable attributes

Name	Default value	Configurable values
AllowCoercion	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#date--time

Style/DefWithParentheses

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for parentheses in the definition of a method, that does not take any arguments. Both instance and class/singleton methods are checked.

Examples

# bad
def foo()
  # does a thing
end

# good
def foo
  # does a thing
end

# also good
def foo() does_a_thing end

# bad
def Baz.foo()
  # does a thing
end

# good
def Baz.foo
  # does a thing
end

References

• https://github.com/rubocop-hq/ruby-style-guide#method-parens

Style/Dir

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for places where the #__dir__ method can replace more complex constructs to retrieve a canonicalized absolute path to the current file.

Examples

# bad
path = File.expand_path(File.dirname(__FILE__))

# bad
path = File.dirname(File.realpath(__FILE__))

# good
path = __dir__

Style/Documentation

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for missing top-level documentation of classes and modules. Classes with no body are exempt from the check and so are namespace modules - modules that have nothing in their bodies except classes, other modules, or constant definitions.

The documentation requirement is annulled if the class or module has a "#:nodoc:" comment next to it. Likewise, "#:nodoc: all" does the same for all its children.

Examples

# bad
class Person
  # ...
end

# good
# Description/Explanation of Person class
class Person
  # ...
end

Configurable attributes

Name	Default value	Configurable values
Exclude	spec/**/*, test/**/*	Array

Style/DocumentationMethod

Enabled by default	Supports autocorrection
Disabled	No

This cop checks for missing documentation comment for public methods. It can optionally be configured to also require documentation for non-public methods.

Examples

# bad

class Foo
  def bar
    puts baz
  end
end

module Foo
  def bar
    puts baz
  end
end

def foo.bar
  puts baz
end

# good

class Foo
  # Documentation
  def bar
    puts baz
  end
end

module Foo
  # Documentation
  def bar
    puts baz
  end
end

# Documentation
def foo.bar
  puts baz
end

Configurable attributes

Name	Default value	Configurable values
Exclude	spec/**/*, test/**/*	Array
RequireForNonPublicMethods	false	Boolean

Style/DoubleNegation

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for uses of double negation (!!) to convert something to a boolean value. As this is both cryptic and usually redundant, it should be avoided.

Please, note that when something is a boolean value !!something and !something.nil? are not the same thing. As you're unlikely to write code that can accept values of any type this is rarely a problem in practice.

Examples

# bad
!!something

# good
!something.nil?

References

• https://github.com/rubocop-hq/ruby-style-guide#no-bang-bang

Style/EachForSimpleLoop

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for loops which iterate a constant number of times, using a Range literal and #each. This can be done more readably using Integer#times.

This check only applies if the block takes no parameters.

Examples

# bad
(1..5).each { }

# good
5.times { }

# bad
(0...10).each {}

# good
10.times {}

Style/EachWithObject

Enabled by default	Supports autocorrection
Enabled	Yes

This cop looks for inject / reduce calls where the passed in object is returned at the end and so could be replaced by each_with_object without the need to return the object at the end.

However, we can't replace with each_with_object if the accumulator parameter is assigned to within the block.

Examples

# bad
[1, 2].inject({}) { |a, e| a[e] = e; a }

# good
[1, 2].each_with_object({}) { |e, a| a[e] = e }

Style/EmptyBlockParameter

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for pipes for empty block parameters. Pipes for empty block parameters do not cause syntax errors, but they are redundant.

Examples

# bad
a do ||
  do_something
end

# bad
a { || do_something }

# good
a do
end

# good
a { do_something }

Style/EmptyCaseCondition

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for case statements with an empty condition.

Examples

# bad:
case
when x == 0
  puts 'x is 0'
when y == 0
  puts 'y is 0'
else
  puts 'neither is 0'
end

# good:
if x == 0
  puts 'x is 0'
elsif y == 0
  puts 'y is 0'
else
  puts 'neither is 0'
end

# good: (the case condition node is not empty)
case n
when 0
  puts 'zero'
when 1
  puts 'one'
else
  puts 'more'
end

Style/EmptyElse

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for empty else-clauses, possibly including comments and/or an explicit nil depending on the EnforcedStyle.

Examples

EnforcedStyle: empty

# warn only on empty else

# bad
if condition
  statement
else
end

# good
if condition
  statement
else
  nil
end

# good
if condition
  statement
else
  statement
end

# good
if condition
  statement
end

EnforcedStyle: nil

# warn on else with nil in it

# bad
if condition
  statement
else
  nil
end

# good
if condition
  statement
else
end

# good
if condition
  statement
else
  statement
end

# good
if condition
  statement
end

EnforcedStyle: both (default)

# warn on empty else and else with nil in it

# bad
if condition
  statement
else
  nil
end

# bad
if condition
  statement
else
end

# good
if condition
  statement
else
  statement
end

# good
if condition
  statement
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	both	empty, nil, both

Style/EmptyLambdaParameter

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for parentheses for empty lambda parameters. Parentheses for empty lambda parameters do not cause syntax errors, but they are redundant.

Examples

# bad
-> () { do_something }

# good
-> { do_something }

# good
-> (arg) { do_something(arg) }

Style/EmptyLiteral

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for the use of a method, the result of which would be a literal, like an empty array, hash or string.

Examples

# bad
a = Array.new
h = Hash.new
s = String.new

# good
a = []
h = {}
s = ''

References

• https://github.com/rubocop-hq/ruby-style-guide#literal-array-hash

Style/EmptyMethod

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for the formatting of empty method definitions. By default it enforces empty method definitions to go on a single line (compact style), but it can be configured to enforce the end to go on its own line (expanded style).

Note: A method definition is not considered empty if it contains comments.

Examples

EnforcedStyle: compact (default)

# bad
def foo(bar)
end

def self.foo(bar)
end

# good
def foo(bar); end

def foo(bar)
  # baz
end

def self.foo(bar); end

EnforcedStyle: expanded

# bad
def foo(bar); end

def self.foo(bar); end

# good
def foo(bar)
end

def self.foo(bar)
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	compact	compact, expanded

References

• https://github.com/rubocop-hq/ruby-style-guide#no-single-line-methods

Style/Encoding

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks ensures source files have no utf-8 encoding comments.

Examples

# bad
# encoding: UTF-8
# coding: UTF-8
# -*- coding: UTF-8 -*-

References

• https://github.com/rubocop-hq/ruby-style-guide#utf-8

Style/EndBlock

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for END blocks.

Examples

# bad
END { puts 'Goodbye!' }

# good
at_exit { puts 'Goodbye!' }

References

• https://github.com/rubocop-hq/ruby-style-guide#no-END-blocks

Style/EvalWithLocation

Enabled by default	Supports autocorrection
Enabled	No

This cop checks eval method usage. eval can receive source location metadata, that are filename and line number. The metadata is used by backtraces. This cop recommends to pass the metadata to eval method.

Examples

# bad
eval <<-RUBY
  def do_something
  end
RUBY

# bad
C.class_eval <<-RUBY
  def do_something
  end
RUBY

# good
eval <<-RUBY, binding, __FILE__, __LINE__ + 1
  def do_something
  end
RUBY

# good
C.class_eval <<-RUBY, __FILE__, __LINE__ + 1
  def do_something
  end
RUBY

Style/EvenOdd

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for places where Integer#even? or Integer#odd? should have been used.

Examples

# bad
if x % 2 == 0
end

# good
if x.even?
end

References

• https://github.com/rubocop-hq/ruby-style-guide#predicate-methods

Style/ExpandPathArguments

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for use of the File.expand_path arguments. Likewise, it also checks for the Pathname.new argument.

Contrastive bad case and good case are alternately shown in the following examples.

Examples

# bad
File.expand_path('..', __FILE__)

# good
File.expand_path(__dir__)

# bad
File.expand_path('../..', __FILE__)

# good
File.expand_path('..', __dir__)

# bad
File.expand_path('.', __FILE__)

# good
File.expand_path(__FILE__)

# bad
Pathname(__FILE__).parent.expand_path

# good
Pathname(__dir__).expand_path

# bad
Pathname.new(__FILE__).parent.expand_path

# good
Pathname.new(__dir__).expand_path

Style/FlipFlop

Enabled by default	Supports autocorrection
Enabled	No

This cop looks for uses of flip flop operator

Examples

# bad
(1..20).each do |x|
  puts x if (x == 5) .. (x == 10)
end

# good
(1..20).each do |x|
  puts x if (x >= 5) && (x <= 10)
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-flip-flops

Style/For

Enabled by default	Supports autocorrection
Enabled	Yes

This cop looks for uses of the for keyword, or each method. The preferred alternative is set in the EnforcedStyle configuration parameter. An each call with a block on a single line is always allowed, however.

Examples

EnforcedStyle: each (default)

# bad
def foo
  for n in [1, 2, 3] do
    puts n
  end
end

# good
def foo
  [1, 2, 3].each do |n|
    puts n
  end
end

EnforcedStyle: for

# bad
def foo
  [1, 2, 3].each do |n|
    puts n
  end
end

# good
def foo
  for n in [1, 2, 3] do
    puts n
  end
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	each	each, for

References

• https://github.com/rubocop-hq/ruby-style-guide#no-for-loops

Style/FormatString

Enabled by default	Supports autocorrection
Enabled	Yes

This cop enforces the use of a single string formatting utility. Valid options include Kernel#format, Kernel#sprintf and String#%.

The detection of String#% cannot be implemented in a reliable manner for all cases, so only two scenarios are considered - if the first argument is a string literal and if the second argument is an array literal.

Examples

EnforcedStyle: format (default)

# bad
puts sprintf('%10s', 'hoge')
puts '%10s' % 'hoge'

# good
puts format('%10s', 'hoge')

EnforcedStyle: sprintf

# bad
puts format('%10s', 'hoge')
puts '%10s' % 'hoge'

# good
puts sprintf('%10s', 'hoge')

EnforcedStyle: percent

# bad
puts format('%10s', 'hoge')
puts sprintf('%10s', 'hoge')

# good
puts '%10s' % 'hoge'

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	format	format, sprintf, percent

References

• https://github.com/rubocop-hq/ruby-style-guide#sprintf

Style/FormatStringToken

Enabled by default	Supports autocorrection
Enabled	No

Use a consistent style for named format string tokens.

Note: unannotated style cop only works for strings which are passed as arguments to those methods: sprintf, format, %. The reason is that unannotated format is very similar to encoded URLs or Date/Time formatting strings.

Examples

EnforcedStyle: annotated (default)

# bad
format('%{greeting}', greeting: 'Hello')
format('%s', 'Hello')

# good
format('%<greeting>s', greeting: 'Hello')

EnforcedStyle: template

# bad
format('%<greeting>s', greeting: 'Hello')
format('%s', 'Hello')

# good
format('%{greeting}', greeting: 'Hello')

EnforcedStyle: unannotated

# bad
format('%<greeting>s', greeting: 'Hello')
format('%{greeting}', 'Hello')

# good
format('%s', 'Hello')

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	annotated	annotated, template, unannotated

Style/FrozenStringLiteralComment

Enabled by default	Supports autocorrection
Enabled	Yes

This cop is designed to help upgrade to Ruby 3.0. It will add the comment # frozen_string_literal: true to the top of files to enable frozen string literals. Frozen string literals may be default in Ruby 3.0. The comment will be added below a shebang and encoding comment. The frozen string literal comment is only valid in Ruby 2.3+.

Examples

EnforcedStyle: when_needed (default)

# The `when_needed` style will add the frozen string literal comment
# to files only when the `TargetRubyVersion` is set to 2.3+.
# bad
module Foo
  # ...
end

# good
# frozen_string_literal: true

module Foo
  # ...
end

EnforcedStyle: always

# The `always` style will always add the frozen string literal comment
# to a file, regardless of the Ruby version or if `freeze` or `<<` are
# called on a string literal.
# bad
module Bar
  # ...
end

# good
# frozen_string_literal: true

module Bar
  # ...
end

EnforcedStyle: never

# The `never` will enforce that the frozen string literal comment does
# not exist in a file.
# bad
# frozen_string_literal: true

module Baz
  # ...
end

# good
module Baz
  # ...
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	when_needed	when_needed, always, never

Style/GlobalVars

Enabled by default	Supports autocorrection
Enabled	No

This cops looks for uses of global variables. It does not report offenses for built-in global variables. Built-in global variables are allowed by default. Additionally users can allow additional variables via the AllowedVariables option.

Note that backreferences like $1, $2, etc are not global variables.

Examples

# bad
$foo = 2
bar = $foo + 5

# good
FOO = 2
foo = 2
$stdin.read

Configurable attributes

Name	Default value	Configurable values
AllowedVariables	[]	Array

References

• https://github.com/rubocop-hq/ruby-style-guide#instance-vars
• http://www.zenspider.com/Languages/Ruby/QuickRef.html

Style/GuardClause

Enabled by default	Supports autocorrection
Enabled	No

Use a guard clause instead of wrapping the code inside a conditional expression

Examples

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok

Configurable attributes

Name	Default value	Configurable values
MinBodyLength	1	Integer

References

• https://github.com/rubocop-hq/ruby-style-guide#no-nested-conditionals

Style/HashSyntax

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks hash literal syntax.

It can enforce either the use of the class hash rocket syntax or the use of the newer Ruby 1.9 syntax (when applicable).

A separate offense is registered for each problematic pair.

The supported styles are:

• ruby19 - forces use of the 1.9 syntax (e.g. {a: 1}) when hashes have all symbols for keys
• hash_rockets - forces use of hash rockets for all hashes
• no_mixed_keys - simply checks for hashes with mixed syntaxes
• ruby19_no_mixed_keys - forces use of ruby 1.9 syntax and forbids mixed syntax hashes

Examples

EnforcedStyle: ruby19 (default)

# bad
{:a => 2}
{b: 1, :c => 2}

# good
{a: 2, b: 1}
{:c => 2, 'd' => 2} # acceptable since 'd' isn't a symbol
{d: 1, 'e' => 2} # technically not forbidden

EnforcedStyle: hash_rockets

# bad
{a: 1, b: 2}
{c: 1, 'd' => 5}

# good
{:a => 1, :b => 2}

EnforcedStyle: no_mixed_keys

# bad
{:a => 1, b: 2}
{c: 1, 'd' => 2}

# good
{:a => 1, :b => 2}
{c: 1, d: 2}

EnforcedStyle: ruby19_no_mixed_keys

# bad
{:a => 1, :b => 2}
{c: 2, 'd' => 3} # should just use hash rockets

# good
{a: 1, b: 2}
{:c => 3, 'd' => 4}

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	ruby19	ruby19, hash_rockets, no_mixed_keys, ruby19_no_mixed_keys
UseHashRocketsWithSymbolValues	false	Boolean
PreferHashRocketsForNonAlnumEndingSymbols	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#hash-literals

Style/IdenticalConditionalBranches

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for identical lines at the beginning or end of each branch of a conditional statement.

Examples

# bad
if condition
  do_x
  do_z
else
  do_y
  do_z
end

# good
if condition
  do_x
else
  do_y
end
do_z

# bad
if condition
  do_z
  do_x
else
  do_z
  do_y
end

# good
do_z
if condition
  do_x
else
  do_y
end

# bad
case foo
when 1
  do_x
when 2
  do_x
else
  do_x
end

# good
case foo
when 1
  do_x
  do_y
when 2
  # nothing
else
  do_x
  do_z
end

Style/IfInsideElse

Enabled by default	Supports autocorrection
Enabled	No

If the else branch of a conditional consists solely of an if node, it can be combined with the else to become an elsif. This helps to keep the nesting level from getting too deep.

Examples

# bad
if condition_a
  action_a
else
  if condition_b
    action_b
  else
    action_c
  end
end

# good
if condition_a
  action_a
elsif condition_b
  action_b
else
  action_c
end

Style/IfUnlessModifier

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for if and unless statements that would fit on one line if written as a modifier if/unless. The maximum line length is configured in the Metrics/LineLength cop. The tab size is configured in the IndentationWidth of the Layout/Tab cop.

Examples

# bad
if condition
  do_stuff(bar)
end

unless qux.empty?
  Foo.do_something
end

# good
do_stuff(bar) if condition
Foo.do_something unless qux.empty?

References

• https://github.com/rubocop-hq/ruby-style-guide#if-as-a-modifier

Style/IfUnlessModifierOfIfUnless

Enabled by default	Supports autocorrection
Enabled	No

Checks for if and unless statements used as modifiers of other if or unless statements.

Examples

# bad
tired? ? 'stop' : 'go faster' if running?

# bad
if tired?
  "please stop"
else
  "keep going"
end if running?

# good
if running?
  tired? ? 'stop' : 'go faster'
end

Style/IfWithSemicolon

Enabled by default	Supports autocorrection
Enabled	No

Checks for uses of semicolon in if statements.

Examples

# bad
result = if some_condition; something else another_thing end

# good
result = some_condition ? something : another_thing

References

• https://github.com/rubocop-hq/ruby-style-guide#no-semicolon-ifs

Style/ImplicitRuntimeError

Enabled by default	Supports autocorrection
Disabled	No

This cop checks for raise or fail statements which do not specify an explicit exception class. (This raises a RuntimeError. Some projects might prefer to use exception classes which more precisely identify the nature of the error.)

Examples

# bad
raise 'Error message here'

# good
raise ArgumentError, 'Error message here'

Style/InfiniteLoop

Enabled by default	Supports autocorrection
Enabled	Yes

Use Kernel#loop for infinite loops.

Examples

# bad
while true
  work
end

# good
loop do
  work
end

References

• https://github.com/rubocop-hq/ruby-style-guide#infinite-loop

Style/InlineComment

Enabled by default	Supports autocorrection
Disabled	No

This cop checks for trailing inline comments.

Examples

# good
foo.each do |f|
  # Standalone comment
  f.bar
end

# bad
foo.each do |f|
  f.bar # Trailing inline comment
end

Style/InverseMethods

Enabled by default	Supports autocorrection
Enabled	Yes

This cop check for usages of not (not or !) called on a method when an inverse of that method can be used instead. Methods that can be inverted by a not (not or !) should be defined in InverseMethods Methods that are inverted by inverting the return of the block that is passed to the method should be defined in InverseBlocks

Examples

# bad
!foo.none?
!foo.any? { |f| f.even? }
!foo.blank?
!(foo == bar)
foo.select { |f| !f.even? }
foo.reject { |f| f != 7 }

# good
foo.none?
foo.blank?
foo.any? { |f| f.even? }
foo != bar
foo == bar
!!('foo' =~ /^\w+$/)
!(foo.class < Numeric) # Checking class hierarchy is allowed

Configurable attributes

Name	Default value	Configurable values
InverseMethods	{:any?=>:none?, :even?=>:odd?, :===>:!=, :=~=>:!~, :<=>:>=, :>=>:<=}
InverseBlocks	{:select=>:reject, :select!=>:reject!}

Style/IpAddresses

Enabled by default	Supports autocorrection
Disabled	No

This cop checks for hardcoded IP addresses, which can make code brittle. IP addresses are likely to need to be changed when code is deployed to a different server or environment, which may break a deployment if forgotten. Prefer setting IP addresses in ENV or other configuration.

Examples

# bad
ip_address = '127.59.241.29'

# good
ip_address = ENV['DEPLOYMENT_IP_ADDRESS']

Configurable attributes

Name	Default value	Configurable values
Whitelist	::	Array

Style/Lambda

Enabled by default	Supports autocorrection
Enabled	Yes

This cop (by default) checks for uses of the lambda literal syntax for single line lambdas, and the method call syntax for multiline lambdas. It is configurable to enforce one of the styles for both single line and multiline lambdas as well.

Examples

EnforcedStyle: line_count_dependent (default)

# bad
f = lambda { |x| x }
f = ->(x) do
      x
    end

# good
f = ->(x) { x }
f = lambda do |x|
      x
    end

EnforcedStyle: lambda

# bad
f = ->(x) { x }
f = ->(x) do
      x
    end

# good
f = lambda { |x| x }
f = lambda do |x|
      x
    end

EnforcedStyle: literal

# bad
f = lambda { |x| x }
f = lambda do |x|
      x
    end

# good
f = ->(x) { x }
f = ->(x) do
      x
    end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	line_count_dependent	line_count_dependent, lambda, literal

References

• https://github.com/rubocop-hq/ruby-style-guide#lambda-multi-line

Style/LambdaCall

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for use of the lambda.(args) syntax.

Examples

EnforcedStyle: call (default)

# bad
lambda.(x, y)

# good
lambda.call(x, y)

EnforcedStyle: braces

# bad
lambda.call(x, y)

# good
lambda.(x, y)

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	call	call, braces

References

• https://github.com/rubocop-hq/ruby-style-guide#proc-call

Style/LineEndConcatenation

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for string literal concatenation at the end of a line.

Examples

# bad
some_str = 'ala' +
           'bala'

some_str = 'ala' <<
           'bala'

# good
some_str = 'ala' \
           'bala'

Style/MethodCallWithArgsParentheses

Enabled by default	Supports autocorrection
Disabled	Yes

This cop checks presence of parentheses in method calls containing parameters. By default, macro methods are ignored. Additional methods can be added to the IgnoredMethods list.

Examples

# bad
array.delete e

# good
array.delete(e)

# good
# Operators don't need parens
foo == bar

# good
# Setter methods don't need parens
foo.bar = baz

# okay with `puts` listed in `IgnoredMethods`
puts 'test'

# IgnoreMacros: true (default)

# good
class Foo
  bar :baz
end

# IgnoreMacros: false

# bad
class Foo
  bar :baz
end

Configurable attributes

Name	Default value	Configurable values
IgnoreMacros	true	Boolean
IgnoredMethods	[]	Array

References

• https://github.com/rubocop-hq/ruby-style-guide#method-invocation-parens

Style/MethodCallWithoutArgsParentheses

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for unwanted parentheses in parameterless method calls.

Examples

# bad
object.some_method()

# good
object.some_method

Configurable attributes

Name	Default value	Configurable values
IgnoredMethods	[]	Array

References

• https://github.com/rubocop-hq/ruby-style-guide#method-invocation-parens

Style/MethodCalledOnDoEndBlock

Enabled by default	Supports autocorrection
Disabled	No

This cop checks for methods called on a do...end block. The point of this check is that it's easy to miss the call tacked on to the block when reading code.

Examples

a do
  b
end.c

References

• https://github.com/rubocop-hq/ruby-style-guide#single-line-blocks

Style/MethodDefParentheses

Enabled by default	Supports autocorrection
Enabled	Yes

This cops checks for parentheses around the arguments in method definitions. Both instance and class/singleton methods are checked.

Examples

EnforcedStyle: require_parentheses (default)

# The `require_parentheses` style requires method definitions
# to always use parentheses

# bad
def bar num1, num2
  num1 + num2
end

def foo descriptive_var_name,
        another_descriptive_var_name,
        last_descriptive_var_name
  do_something
end

# good
def bar(num1, num2)
  num1 + num2
end

def foo(descriptive_var_name,
        another_descriptive_var_name,
        last_descriptive_var_name)
  do_something
end

EnforcedStyle: require_no_parentheses

# The `require_no_parentheses` style requires method definitions
# to never use parentheses

# bad
def bar(num1, num2)
  num1 + num2
end

def foo(descriptive_var_name,
        another_descriptive_var_name,
        last_descriptive_var_name)
  do_something
end

# good
def bar num1, num2
  num1 + num2
end

def foo descriptive_var_name,
        another_descriptive_var_name,
        last_descriptive_var_name
  do_something
end

EnforcedStyle: require_no_parentheses_except_multiline

# The `require_no_parentheses_except_multiline` style prefers no
# parentheses when method definition arguments fit on single line,
# but prefers parentheses when arguments span multiple lines.

# bad
def bar(num1, num2)
  num1 + num2
end

def foo descriptive_var_name,
        another_descriptive_var_name,
        last_descriptive_var_name
  do_something
end

# good
def bar num1, num2
  num1 + num2
end

def foo(descriptive_var_name,
        another_descriptive_var_name,
        last_descriptive_var_name)
  do_something
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	require_parentheses	require_parentheses, require_no_parentheses, require_no_parentheses_except_multiline

References

• https://github.com/rubocop-hq/ruby-style-guide#method-parens

Style/MethodMissingSuper

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for the presence of method_missing without falling back on super.

Examples

#bad
def method_missing(name, *args)
  # ...
end

#good

def method_missing(name, *args)
  # ...
  super
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-method-missing

Style/MinMax

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for potential uses of Enumerable#minmax.

Examples

# bad
bar = [foo.min, foo.max]
return foo.min, foo.max

# good
bar = foo.minmax
return foo.minmax

Style/MissingElse

Enabled by default	Supports autocorrection
Disabled	No

Checks for if expressions that do not have an else branch.

Supported styles are: if, case, both.

Examples

EnforcedStyle: if

# warn when an `if` expression is missing an `else` branch.

# bad
if condition
  statement
end

# good
if condition
  statement
else
  # the content of `else` branch will be determined by Style/EmptyElse
end

# good
case var
when condition
  statement
end

# good
case var
when condition
  statement
else
  # the content of `else` branch will be determined by Style/EmptyElse
end

EnforcedStyle: case

# warn when a `case` expression is missing an `else` branch.

# bad
case var
when condition
  statement
end

# good
case var
when condition
  statement
else
  # the content of `else` branch will be determined by Style/EmptyElse
end

# good
if condition
  statement
end

# good
if condition
  statement
else
  # the content of `else` branch will be determined by Style/EmptyElse
end

EnforcedStyle: both (default)

# warn when an `if` or `case` expression is missing an `else` branch.

# bad
if condition
  statement
end

# bad
case var
when condition
  statement
end

# good
if condition
  statement
else
  # the content of `else` branch will be determined by Style/EmptyElse
end

# good
case var
when condition
  statement
else
  # the content of `else` branch will be determined by Style/EmptyElse
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	both	if, case, both

Style/MissingRespondToMissing

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for the presence of method_missing without also defining respond_to_missing?.

Examples

#bad
def method_missing(name, *args)
  # ...
end

#good
def respond_to_missing?(name, include_private)
  # ...
end

def method_missing(name, *args)
  # ...
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-method-missing

Style/MixinGrouping

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for grouping of mixins in class and module bodies. By default it enforces mixins to be placed in separate declarations, but it can be configured to enforce grouping them in one declaration.

Examples

EnforcedStyle: separated (default)

# bad
class Foo
  include Bar, Qox
end

# good
class Foo
  include Qox
  include Bar
end

EnforcedStyle: grouped

# bad
class Foo
  extend Bar
  extend Qox
end

# good
class Foo
  extend Qox, Bar
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	separated	separated, grouped

References

• https://github.com/rubocop-hq/ruby-style-guide#mixin-grouping

Style/MixinUsage

Enabled by default	Supports autocorrection
Enabled	No

This cop checks that include, extend and prepend statements appear inside classes and modules, not at the top level, so as to not affect the behavior of Object.

Examples

# bad
include M

class C
end

# bad
extend M

class C
end

# bad
prepend M

class C
end

# good
class C
  include M
end

# good
class C
  extend M
end

# good
class C
  prepend M
end

Style/ModuleFunction

Enabled by default	Supports autocorrection
Enabled	Yes

This cops checks for use of extend self or module_function in a module.

Supported styles are: module_function, extend_self.

These offenses are not auto-corrected since there are different implications to each approach.

Examples

EnforcedStyle: module_function (default)

# bad
module Test
  extend self
  # ...
end

# good
module Test
  module_function
  # ...
end

EnforcedStyle: extend_self

# bad
module Test
  module_function
  # ...
end

# good
module Test
  extend self
  # ...
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	module_function	module_function, extend_self

References

• https://github.com/rubocop-hq/ruby-style-guide#module-function

Style/MultilineBlockChain

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for chaining of a block after another block that spans multiple lines.

Examples

Thread.list.find_all do |t|
  t.alive?
end.map do |t|
  t.object_id
end

References

• https://github.com/rubocop-hq/ruby-style-guide#single-line-blocks

Style/MultilineIfModifier

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for uses of if/unless modifiers with multiple-lines bodies.

Examples

# bad
{
  result: 'this should not happen'
} unless cond

# good
{ result: 'ok' } if cond

References

• https://github.com/rubocop-hq/ruby-style-guide#no-multiline-if-modifiers

Style/MultilineIfThen

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for uses of the then keyword in multi-line if statements.

Examples

# bad
# This is considered bad practice.
if cond then
end

# good
# If statements can contain `then` on the same line.
if cond then a
elsif cond then b
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-then

Style/MultilineMemoization

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks expressions wrapping styles for multiline memoization.

Examples

EnforcedStyle: keyword (default)

# bad
foo ||= (
  bar
  baz
)

# good
foo ||= begin
  bar
  baz
end

EnforcedStyle: braces

# bad
foo ||= begin
  bar
  baz
end

# good
foo ||= (
  bar
  baz
)

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	keyword	keyword, braces

Style/MultilineTernaryOperator

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for multi-line ternary op expressions.

Examples

# bad
a = cond ?
  b : c
a = cond ? b :
    c
a = cond ?
    b :
    c

# good
a = cond ? b : c
a =
  if cond
    b
  else
    c
  end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-multiline-ternary

Style/MultipleComparison

Enabled by default	Supports autocorrection
Enabled	No

This cop checks against comparing a variable with multiple items, where Array#include? could be used instead to avoid code repetition.

Examples

# bad
a = 'a'
foo if a == 'a' || a == 'b' || a == 'c'

# good
a = 'a'
foo if ['a', 'b', 'c'].include?(a)

Style/MutableConstant

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks whether some constant value isn't a mutable literal (e.g. array or hash).

Examples

# bad
CONST = [1, 2, 3]

# good
CONST = [1, 2, 3].freeze

# good
CONST = <<~TESTING.freeze
This is a heredoc
TESTING

Style/NegatedIf

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for uses of if with a negated condition. Only ifs without else are considered. There are three different styles:

• both
• prefix
• postfix

Examples

EnforcedStyle: both (default)

# enforces `unless` for `prefix` and `postfix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# bad

bar if !foo

# good

bar unless foo

EnforcedStyle: prefix

# enforces `unless` for just `prefix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# good

bar if !foo

EnforcedStyle: postfix

# enforces `unless` for just `postfix` conditionals

# bad

bar if !foo

# good

bar unless foo

# good

if !foo
  bar
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	both	both, prefix, postfix

References

• https://github.com/rubocop-hq/ruby-style-guide#unless-for-negatives

Style/NegatedWhile

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for uses of while with a negated condition.

Examples

# bad
while !foo
  bar
end

# good
until foo
  bar
end

# bad
bar until !foo

# good
bar while foo
bar while !foo && baz

References

• https://github.com/rubocop-hq/ruby-style-guide#until-for-negatives

Style/NestedModifier

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for nested use of if, unless, while and until in their modifier form.

Examples

# bad
something if a if b

# good
something if b && a

References

• https://github.com/rubocop-hq/ruby-style-guide#no-nested-modifiers

Style/NestedParenthesizedCalls

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for unparenthesized method calls in the argument list of a parenthesized method call.

Examples

# good
method1(method2(arg), method3(arg))

# bad
method1(method2 arg, method3, arg)

Configurable attributes

Name	Default value	Configurable values
Whitelist	be, be_a, be_an, be_between, be_falsey, be_kind_of, be_instance_of, be_truthy, be_within, eq, eql, end_with, include, match, raise_error, respond_to, start_with	Array

Style/NestedTernaryOperator

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for nested ternary op expressions.

Examples

# bad
a ? (b ? b1 : b2) : a2

# good
if a
  b ? b1 : b2
else
  a2
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-nested-ternary

Style/Next

Enabled by default	Supports autocorrection
Enabled	Yes

Use next to skip iteration instead of a condition at the end.

Examples

EnforcedStyle: skip_modifier_ifs (default)

# bad
[1, 2].each do |a|
  if a == 1
    puts a
  end
end

# good
[1, 2].each do |a|
  next unless a == 1
  puts a
end

# good
[1, 2].each do |o|
  puts o unless o == 1
end

EnforcedStyle: always

# With `always` all conditions at the end of an iteration needs to be
# replaced by next - with `skip_modifier_ifs` the modifier if like
# this one are ignored: `[1, 2].each { |a| return 'yes' if a == 1 }`

# bad
[1, 2].each do |o|
  puts o unless o == 1
end

# bad
[1, 2].each do |a|
  if a == 1
    puts a
  end
end

# good
[1, 2].each do |a|
  next unless a == 1
  puts a
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	skip_modifier_ifs	skip_modifier_ifs, always
MinBodyLength	3	Integer

References

• https://github.com/rubocop-hq/ruby-style-guide#no-nested-conditionals

Style/NilComparison

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for comparison of something with nil using == and nil?.

Supported styles are: predicate, comparison.

Examples

EnforcedStyle: predicate (default)

# bad
if x == nil
end

# good
if x.nil?
end

EnforcedStyle: comparison

# bad
if x.nil?
end

# good
if x == nil
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	predicate	predicate, comparison

References

• https://github.com/rubocop-hq/ruby-style-guide#predicate-methods

Style/NonNilCheck

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for non-nil checks, which are usually redundant.

Non-nil checks are allowed if they are the final nodes of predicate.

good

def signed_in? !current_user.nil? end

Examples

# bad
if x != nil
end

# good (when not allowing semantic changes)
# bad (when allowing semantic changes)
if !x.nil?
end

# good (when allowing semantic changes)
if x
end

Configurable attributes

Name	Default value	Configurable values
IncludeSemanticChanges	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#no-non-nil-checks

Style/Not

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for uses of the keyword not instead of !.

Examples

# bad - parentheses are required because of op precedence
x = (not something)

# good
x = !something

References

• https://github.com/rubocop-hq/ruby-style-guide#bang-not-not

Style/NumericLiteralPrefix

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for octal, hex, binary and decimal literals using uppercase prefixes and corrects them to lowercase prefix or no prefix (in case of decimals).

Examples

EnforcedOctalStyle: zero_with_o (default)

# bad - missing octal prefix
num = 01234

# bad - uppercase prefix
num = 0O1234
num = 0X12AB
num = 0B10101

# bad - redundant decimal prefix
num = 0D1234
num = 0d1234

# good
num = 0o1234
num = 0x12AB
num = 0b10101
num = 1234

EnforcedOctalStyle: zero_only

# bad
num = 0o1234
num = 0O1234

# good
num = 01234

Configurable attributes

Name	Default value	Configurable values
EnforcedOctalStyle	zero_with_o	zero_with_o, zero_only

References

• https://github.com/rubocop-hq/ruby-style-guide#numeric-literal-prefixes

Style/NumericLiterals

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for big numeric literals without _ between groups of digits in them.

Examples

# bad

1000000
1_00_000
1_0000

# good

1_000_000
1000

# good unless Strict is set

10_000_00 # typical representation of $10,000 in cents

Configurable attributes

Name	Default value	Configurable values
MinDigits	5	Integer
Strict	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#underscores-in-numerics

Style/NumericPredicate

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for usage of comparison operators (==, >, <) to test numbers as zero, positive, or negative. These can be replaced by their respective predicate methods. The cop can also be configured to do the reverse.

The cop disregards #nonzero? as it its value is truthy or falsey, but not true and false, and thus not always interchangeable with != 0.

The cop ignores comparisons to global variables, since they are often populated with objects which can be compared with integers, but are not themselves Integer polymorphic.

Examples

EnforcedStyle: predicate (default)

# bad

foo == 0
0 > foo
bar.baz > 0

# good

foo.zero?
foo.negative?
bar.baz.positive?

EnforcedStyle: comparison

# bad

foo.zero?
foo.negative?
bar.baz.positive?

# good

foo == 0
0 > foo
bar.baz > 0

Configurable attributes

Name	Default value	Configurable values
AutoCorrect	false	Boolean
EnforcedStyle	predicate	predicate, comparison
IgnoredMethods	[]	Array
Exclude	spec/**/*	Array

References

• https://github.com/rubocop-hq/ruby-style-guide#predicate-methods

Style/OneLineConditional

Enabled by default	Supports autocorrection
Enabled	Yes

TODO: Make configurable. Checks for uses of if/then/else/end on a single line.

Examples

# bad
if foo then boo else doo end
unless foo then boo else goo end

# good
foo ? boo : doo
boo if foo
if foo then boo end

# good
if foo
  boo
else
  doo
end

References

• https://github.com/rubocop-hq/ruby-style-guide#ternary-operator

Style/OptionHash

Enabled by default	Supports autocorrection
Disabled	No

This cop checks for options hashes and discourages them if the current Ruby version supports keyword arguments.

Examples

# bad
def fry(options = {})
  temperature = options.fetch(:temperature, 300)
  # ...
end

# good
def fry(temperature: 300)
  # ...
end

Configurable attributes

Name	Default value	Configurable values
SuspiciousParamNames	options, opts, args, params, parameters	Array

Style/OptionalArguments

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for optional arguments to methods that do not come at the end of the argument list

Examples

# bad
def foo(a = 1, b, c)
end

# good
def baz(a, b, c = 1)
end

def foobar(a = 1, b = 2, c = 3)
end

References

• https://github.com/rubocop-hq/ruby-style-guide#optional-arguments

Style/OrAssignment

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for potential usage of the ||= operator.

Examples

# bad
name = name ? name : 'Bozhidar'

# bad
name = if name
         name
       else
         'Bozhidar'
       end

# bad
unless name
  name = 'Bozhidar'
end

# bad
name = 'Bozhidar' unless name

# good - set name to 'Bozhidar', only if it's nil or false
name ||= 'Bozhidar'

References

• https://github.com/rubocop-hq/ruby-style-guide#double-pipe-for-uninit

Style/ParallelAssignment

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for simple usages of parallel assignment. This will only complain when the number of variables being assigned matched the number of assigning variables.

Examples

# bad
a, b, c = 1, 2, 3
a, b, c = [1, 2, 3]

# good
one, two = *foo
a, b = foo()
a, b = b, a

a = 1
b = 2
c = 3

References

• https://github.com/rubocop-hq/ruby-style-guide#parallel-assignment

Style/ParenthesesAroundCondition

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for the presence of superfluous parentheses around the condition of if/unless/while/until.

Examples

# bad
x += 1 while (x < 10)
foo unless (bar || baz)

if (x > 10)
elsif (x < 3)
end

# good
x += 1 while x < 10
foo unless bar || baz

if x > 10
elsif x < 3
end

AllowInMultilineConditions: false (default)

# bad
if (x > 10 &&
   y > 10)
end

# good
 if x > 10 &&
    y > 10
 end

AllowInMultilineConditions: true

# good
if (x > 10 &&
   y > 10)
end

Configurable attributes

Name	Default value	Configurable values
AllowSafeAssignment	true	Boolean
AllowInMultilineConditions	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#no-parens-around-condition

Style/PercentLiteralDelimiters

Enabled by default	Supports autocorrection
Enabled	Yes

This cop enforces the consistent usage of %-literal delimiters.

Specify the 'default' key to set all preferred delimiters at once. You can continue to specify individual preferred delimiters to override the default.

Examples

# Style/PercentLiteralDelimiters:
#   PreferredDelimiters:
#     default: '[]'
#     '%i':    '()'

# good
%w[alpha beta] + %i(gamma delta)

# bad
%W(alpha #{beta})

# bad
%I(alpha beta)

Configurable attributes

Name	Default value	Configurable values
PreferredDelimiters	{"default"=>"()", "%i"=>"[]", "%I"=>"[]", "%r"=>"{}", "%w"=>"[]", "%W"=>"[]"}

References

• https://github.com/rubocop-hq/ruby-style-guide#percent-literal-braces

Style/PercentQLiterals

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for usage of the %Q() syntax when %q() would do.

Examples

EnforcedStyle: lower_case_q (default)

# The `lower_case_q` style prefers `%q` unless
# interpolation is needed.
# bad
%Q[Mix the foo into the baz.]
%Q(They all said: 'Hooray!')

# good
%q[Mix the foo into the baz]
%q(They all said: 'Hooray!')

EnforcedStyle: upper_case_q

# The `upper_case_q` style requires the sole use of `%Q`.
# bad
%q/Mix the foo into the baz./
%q{They all said: 'Hooray!'}

# good
%Q/Mix the foo into the baz./
%Q{They all said: 'Hooray!'}

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	lower_case_q	lower_case_q, upper_case_q

Style/PerlBackrefs

Enabled by default	Supports autocorrection
Enabled	Yes

This cop looks for uses of Perl-style regexp match backreferences like $1, $2, etc.

Examples

# bad
puts $1

# good
puts Regexp.last_match(1)

References

• https://github.com/rubocop-hq/ruby-style-guide#no-perl-regexp-last-matchers

Style/PreferredHashMethods

Enabled by default	Supports autocorrection
Enabled	Yes

This cop (by default) checks for uses of methods Hash#has_key? and Hash#has_value? where it enforces Hash#key? and Hash#value? It is configurable to enforce the inverse, using verbose method names also.

Examples

EnforcedStyle: short (default)

# bad
Hash#has_key?
Hash#has_value?

# good
Hash#key?
Hash#value?

EnforcedStyle: verbose

# bad
Hash#key?
Hash#value?

# good
Hash#has_key?
Hash#has_value?

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	short	short, verbose

References

• https://github.com/rubocop-hq/ruby-style-guide#hash-key

Style/Proc

Enabled by default	Supports autocorrection
Enabled	Yes

This cops checks for uses of Proc.new where Kernel#proc would be more appropriate.

Examples

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

# good
p = proc { |n| puts n }

References

• https://github.com/rubocop-hq/ruby-style-guide#proc

Style/RaiseArgs

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks the args passed to fail and raise. For exploded style (default), it recommends passing the exception class and message to raise, rather than construct an instance of the error. It will still allow passing just a message, or the construction of an error with more than one argument.

The exploded style works identically, but with the addition that it will also suggest constructing error objects when the exception is passed multiple arguments.

Examples

EnforcedStyle: exploded (default)

# bad
raise StandardError.new("message")

# good
raise StandardError, "message"
fail "message"
raise MyCustomError.new(arg1, arg2, arg3)
raise MyKwArgError.new(key1: val1, key2: val2)

EnforcedStyle: compact

# bad
raise StandardError, "message"
raise RuntimeError, arg1, arg2, arg3

# good
raise StandardError.new("message")
raise MyCustomError.new(arg1, arg2, arg3)
fail "message"

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	exploded	compact, exploded

References

• https://github.com/rubocop-hq/ruby-style-guide#exception-class-messages

Style/RandomWithOffset

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for the use of randomly generated numbers, added/subtracted with integer literals, as well as those with Integer#succ and Integer#pred methods. Prefer using ranges instead, as it clearly states the intentions.

Examples

# bad
rand(6) + 1
1 + rand(6)
rand(6) - 1
1 - rand(6)
rand(6).succ
rand(6).pred
Random.rand(6) + 1
Kernel.rand(6) + 1
rand(0..5) + 1

# good
rand(1..6)
rand(1...7)

References

• https://github.com/rubocop-hq/ruby-style-guide#random-numbers

Style/RedundantBegin

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for redundant begin blocks.

Currently it checks for code like this:

Examples

# bad
def redundant
  begin
    ala
    bala
  rescue StandardError => e
    something
  end
end

# good
def preferred
  ala
  bala
rescue StandardError => e
  something
end

# bad
# When using Ruby 2.5 or later.
do_something do
  begin
    something
  rescue => ex
    anything
  end
end

# good
# In Ruby 2.5 or later, you can omit `begin` in `do-end` block.
do_something do
  something
rescue => ex
  anything
end

# good
# Stabby lambdas don't support implicit `begin` in `do-end` blocks.
-> do
  begin
    foo
  rescue Bar
    baz
  end
end

References

• https://github.com/rubocop-hq/ruby-style-guide#begin-implicit

Style/RedundantConditional

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for redundant returning of true/false in conditionals.

Examples

# bad
x == y ? true : false

# bad
if x == y
  true
else
  false
end

# good
x == y

# bad
x == y ? false : true

# good
x != y

Style/RedundantException

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for RuntimeError as the argument of raise/fail.

It checks for code like this:

Examples

# Bad
raise RuntimeError, 'message'

# Bad
raise RuntimeError.new('message')

# Good
raise 'message'

References

• https://github.com/rubocop-hq/ruby-style-guide#no-explicit-runtimeerror

Style/RedundantFreeze

Enabled by default	Supports autocorrection
Enabled	Yes

This cop check for uses of Object#freeze on immutable objects.

Examples

# bad
CONST = 1.freeze

# good
CONST = 1

Style/RedundantParentheses

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for redundant parentheses.

Examples

# bad
(x) if ((y.z).nil?)

# good
x if y.z.nil?

Style/RedundantReturn

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for redundant return expressions.

Examples

# These bad cases should be extended to handle methods whose body is
# if/else or a case expression with a default branch.

# bad
def test
  return something
end

# bad
def test
  one
  two
  three
  return something
end

# good
def test
  return something if something_else
end

# good
def test
  if x
  elsif y
  else
  end
end

Configurable attributes

Name	Default value	Configurable values
AllowMultipleReturnValues	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#no-explicit-return

Style/RedundantSelf

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for redundant uses of self.

The usage of self is only needed when:

• Sending a message to same object with zero arguments in presence of a method name clash with an argument or a local variable.

• Calling an attribute writer to prevent an local variable assignment.

Note, with using explicit self you can only send messages with public or protected scope, you cannot send private messages this way.

Note we allow uses of self with operators because it would be awkward otherwise.

Examples

# bad
def foo(bar)
  self.baz
end

# good
def foo(bar)
  self.bar  # Resolves name clash with the argument.
end

def foo
  bar = 1
  self.bar  # Resolves name clash with the local variable.
end

def foo
  %w[x y z].select do |bar|
    self.bar == bar  # Resolves name clash with argument of the block.
  end
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-self-unless-required

Style/RegexpLiteral

Enabled by default	Supports autocorrection
Enabled	Yes

This cop enforces using // or %r around regular expressions.

Examples

EnforcedStyle: slashes (default)

# bad
snake_case = %r{^[\dA-Z_]+$}

# bad
regex = %r{
  foo
  (bar)
  (baz)
}x

# good
snake_case = /^[\dA-Z_]+$/

# good
regex = /
  foo
  (bar)
  (baz)
/x

EnforcedStyle: percent_r

# bad
snake_case = /^[\dA-Z_]+$/

# bad
regex = /
  foo
  (bar)
  (baz)
/x

# good
snake_case = %r{^[\dA-Z_]+$}

# good
regex = %r{
  foo
  (bar)
  (baz)
}x

EnforcedStyle: mixed

# bad
snake_case = %r{^[\dA-Z_]+$}

# bad
regex = /
  foo
  (bar)
  (baz)
/x

# good
snake_case = /^[\dA-Z_]+$/

# good
regex = %r{
  foo
  (bar)
  (baz)
}x

AllowInnerSlashes: false (default)

# If `false`, the cop will always recommend using `%r` if one or more
# slashes are found in the regexp string.

# bad
x =~ /home\//

# good
x =~ %r{home/}

AllowInnerSlashes: true

# good
x =~ /home\//

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	slashes	slashes, percent_r, mixed
AllowInnerSlashes	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#percent-r

Style/RescueModifier

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for uses of rescue in its modifier form.

Examples

# bad
some_method rescue handle_error

# good
begin
  some_method
rescue
  handle_error
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-rescue-modifiers

Style/RescueStandardError

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for rescuing StandardError. There are two supported styles implicit and explicit. This cop will not register an offense if any error other than StandardError is specified.

Examples

EnforcedStyle: implicit

# `implicit` will enforce using `rescue` instead of
# `rescue StandardError`.

# bad
begin
  foo
rescue StandardError
  bar
end

# good
begin
  foo
rescue
  bar
end

# good
begin
  foo
rescue OtherError
  bar
end

# good
begin
  foo
rescue StandardError, SecurityError
  bar
end

EnforcedStyle: explicit (default)

# `explicit` will enforce using `rescue StandardError`
# instead of `rescue`.

# bad
begin
  foo
rescue
  bar
end

# good
begin
  foo
rescue StandardError
  bar
end

# good
begin
  foo
rescue OtherError
  bar
end

# good
begin
  foo
rescue StandardError, SecurityError
  bar
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	explicit	implicit, explicit

Style/ReturnNil

Enabled by default	Supports autocorrection
Disabled	Yes

This cop enforces consistency between 'return nil' and 'return'.

Supported styles are: return, return_nil.

Examples

EnforcedStyle: return (default)

# bad
def foo(arg)
  return nil if arg
end

# good
def foo(arg)
  return if arg
end

EnforcedStyle: return_nil

# bad
def foo(arg)
  return if arg
end

# good
def foo(arg)
  return nil if arg
end

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	return	return, return_nil

Style/SafeNavigation

Enabled by default	Supports autocorrection
Enabled	Yes

This cop transforms usages of a method call safeguarded by a non nil check for the variable whose method is being called to safe navigation (&.). If there is a method chain, all of the methods in the chain need to be checked for safety, and all of the methods will need to be changed to use safe navigation. We have limited the cop to not register an offense for method chains that exceed 2 methods.

Configuration option: ConvertCodeThatCanStartToReturnNil The default for this is false. When configured to true, this will check for code in the format !foo.nil? && foo.bar. As it is written, the return of this code is limited to false and whatever the return of the method is. If this is converted to safe navigation, foo&.bar can start returning nil as well as what the method returns.

Examples

# bad
foo.bar if foo
foo.bar.baz if foo
foo.bar(param1, param2) if foo
foo.bar { |e| e.something } if foo
foo.bar(param) { |e| e.something } if foo

foo.bar if !foo.nil?
foo.bar unless !foo
foo.bar unless foo.nil?

foo && foo.bar
foo && foo.bar.baz
foo && foo.bar(param1, param2)
foo && foo.bar { |e| e.something }
foo && foo.bar(param) { |e| e.something }

# good
foo&.bar
foo&.bar&.baz
foo&.bar(param1, param2)
foo&.bar { |e| e.something }
foo&.bar(param) { |e| e.something }
foo && foo.bar.baz.qux # method chain with more than 2 methods
foo && foo.nil? # method that `nil` responds to

# Method calls that do not use `.`
foo && foo < bar
foo < bar if foo

# This could start returning `nil` as well as the return of the method
foo.nil? || foo.bar
!foo || foo.bar

# Methods that are used on assignment, arithmetic operation or
# comparison should not be converted to use safe navigation
foo.baz = bar if foo
foo.baz + bar if foo
foo.bar > 2 if foo

Configurable attributes

Name	Default value	Configurable values
ConvertCodeThatCanStartToReturnNil	false	Boolean
Whitelist	present?, blank?, presence, try, try!	Array

Style/SelfAssignment

Enabled by default	Supports autocorrection
Enabled	Yes

This cop enforces the use the shorthand for self-assignment.

Examples

# bad
x = x + 1

# good
x += 1

References

• https://github.com/rubocop-hq/ruby-style-guide#self-assignment

Style/Semicolon

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for multiple expressions placed on the same line. It also checks for lines terminated with a semicolon.

Examples

# bad
foo = 1; bar = 2;
baz = 3;

# good
foo = 1
bar = 2
baz = 3

Configurable attributes

Name	Default value	Configurable values
AllowAsExpressionSeparator	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#no-semicolon

Style/Send

Enabled by default	Supports autocorrection
Disabled	No

This cop checks for the use of the send method.

Examples

# bad
Foo.send(:bar)
quuz.send(:fred)

# good
Foo.__send__(:bar)
quuz.public_send(:fred)

References

• https://github.com/rubocop-hq/ruby-style-guide#prefer-public-send

Style/SignalException

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for uses of fail and raise.

Examples

EnforcedStyle: only_raise (default)

# The `only_raise` style enforces the sole use of `raise`.
# bad
begin
  fail
rescue Exception
  # handle it
end

def watch_out
  fail
rescue Exception
  # handle it
end

Kernel.fail

# good
begin
  raise
rescue Exception
  # handle it
end

def watch_out
  raise
rescue Exception
  # handle it
end

Kernel.raise

EnforcedStyle: only_fail

# The `only_fail` style enforces the sole use of `fail`.
# bad
begin
  raise
rescue Exception
  # handle it
end

def watch_out
  raise
rescue Exception
  # handle it
end

Kernel.raise

# good
begin
  fail
rescue Exception
  # handle it
end

def watch_out
  fail
rescue Exception
  # handle it
end

Kernel.fail

EnforcedStyle: semantic

# The `semantic` style enforces the use of `fail` to signal an
# exception, then will use `raise` to trigger an offense after
# it has been rescued.
# bad
begin
  raise
rescue Exception
  # handle it
end

def watch_out
  # Error thrown
rescue Exception
  fail
end

Kernel.fail
Kernel.raise

# good
begin
  fail
rescue Exception
  # handle it
end

def watch_out
  fail
rescue Exception
  raise 'Preferably with descriptive message'
end

explicit_receiver.fail
explicit_receiver.raise

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	only_raise	only_raise, only_fail, semantic

References

• https://github.com/rubocop-hq/ruby-style-guide#prefer-raise-over-fail

Style/SingleLineBlockParams

Enabled by default	Supports autocorrection
Disabled	No

This cop checks whether the block parameters of a single-line method accepting a block match the names specified via configuration.

For instance one can configure reduce(inject) to use |a, e| as parameters.

Configuration option: Methods Should be set to use this cop. Array of hashes, where each key is the method name and value - array of argument names.

Examples

Methods: [{reduce: %w[a b]}]

# bad
foo.reduce { |c, d| c + d }
foo.reduce { |_, _d| 1 }

# good
foo.reduce { |a, b| a + b }
foo.reduce { |a, _b| a }
foo.reduce { |a, (id, _)| a + id }
foo.reduce { true }

# good
foo.reduce do |c, d|
  c + d
end

Configurable attributes

Name	Default value	Configurable values
Methods	{"reduce"=>["acc", "elem"]}, {"inject"=>["acc", "elem"]}	Array

Style/SingleLineMethods

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for single-line method definitions that contain a body. It will accept single-line methods with no body.

Examples

# bad
def some_method; body end
def link_to(url); {:name => url}; end
def @table.columns; super; end

# good
def no_op; end
def self.resource_class=(klass); end
def @table.columns; end

Configurable attributes

Name	Default value	Configurable values
AllowIfMethodIsEmpty	true	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#no-single-line-methods

Style/SpecialGlobalVars

Enabled by default	Supports autocorrection
Enabled	Yes

This cop looks for uses of Perl-style global variables.

Examples

EnforcedStyle: use_english_names (default)

# good
puts $LOAD_PATH
puts $LOADED_FEATURES
puts $PROGRAM_NAME
puts $ERROR_INFO
puts $ERROR_POSITION
puts $FIELD_SEPARATOR # or $FS
puts $OUTPUT_FIELD_SEPARATOR # or $OFS
puts $INPUT_RECORD_SEPARATOR # or $RS
puts $OUTPUT_RECORD_SEPARATOR # or $ORS
puts $INPUT_LINE_NUMBER # or $NR
puts $LAST_READ_LINE
puts $DEFAULT_OUTPUT
puts $DEFAULT_INPUT
puts $PROCESS_ID # or $PID
puts $CHILD_STATUS
puts $LAST_MATCH_INFO
puts $IGNORECASE
puts $ARGV # or ARGV
puts $MATCH
puts $PREMATCH
puts $POSTMATCH
puts $LAST_PAREN_MATCH

EnforcedStyle: use_perl_names

# good
puts $:
puts $"
puts $0
puts $!
puts $@
puts $;
puts $,
puts $/
puts $\
puts $.
puts $_
puts $>
puts $<
puts $$
puts $?
puts $~
puts $=
puts $*
puts $&
puts $`
puts $'
puts $+

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	use_english_names	use_perl_names, use_english_names

References

• https://github.com/rubocop-hq/ruby-style-guide#no-cryptic-perlisms

Style/StabbyLambdaParentheses

Enabled by default	Supports autocorrection
Enabled	Yes

Check for parentheses around stabby lambda arguments. There are two different styles. Defaults to require_parentheses.

Examples

EnforcedStyle: require_parentheses (default)

# bad
->a,b,c { a + b + c }

# good
->(a,b,c) { a + b + c}

EnforcedStyle: require_no_parentheses

# bad
->(a,b,c) { a + b + c }

# good
->a,b,c { a + b + c}

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	require_parentheses	require_parentheses, require_no_parentheses

References

• https://github.com/rubocop-hq/ruby-style-guide#stabby-lambda-with-args

Style/StderrPuts

Enabled by default	Supports autocorrection
Enabled	Yes

This cop identifies places where $stderr.puts can be replaced by warn. The latter has the advantage of easily being disabled by, e.g. the -W0 interpreter flag, or setting $VERBOSE to nil.

Examples

# bad
$stderr.puts('hello')

# good
warn('hello')

References

• https://github.com/rubocop-hq/ruby-style-guide#warn

Style/StringHashKeys

Enabled by default	Supports autocorrection
Disabled	Yes

This cop checks for the use of strings as keys in hashes. The use of symbols is preferred instead.

Examples

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

# good
{ one: 1, two: 2, three: 3 }

References

• https://github.com/rubocop-hq/ruby-style-guide#symbols-as-keys

Style/StringLiterals

Enabled by default	Supports autocorrection
Enabled	Yes

Checks if uses of quotes match the configured preference.

Examples

EnforcedStyle: single_quotes (default)

# bad
"No special symbols"
"No string interpolation"
"Just text"

# good
'No special symbols'
'No string interpolation'
'Just text'
"Wait! What's #{this}!"

EnforcedStyle: double_quotes

# bad
'Just some text'
'No special chars or interpolation'

# good
"Just some text"
"No special chars or interpolation"
"Every string in #{project} uses double_quotes"

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	single_quotes	single_quotes, double_quotes
ConsistentQuotesInMultiline	false	Boolean

References

• https://github.com/rubocop-hq/ruby-style-guide#consistent-string-literals

Style/StringLiteralsInInterpolation

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks that quotes inside the string interpolation match the configured preference.

Examples

EnforcedStyle: single_quotes (default)

# bad
result = "Tests #{success ? "PASS" : "FAIL"}"

# good
result = "Tests #{success ? 'PASS' : 'FAIL'}"

EnforcedStyle: double_quotes

# bad
result = "Tests #{success ? 'PASS' : 'FAIL'}"

# good
result = "Tests #{success ? "PASS" : "FAIL"}"

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	single_quotes	single_quotes, double_quotes

Style/StringMethods

Enabled by default	Supports autocorrection
Disabled	Yes

This cop enforces the use of consistent method names from the String class.

Examples

# bad
'name'.intern
'var'.unfavored_method

# good
'name'.to_sym
'var'.preferred_method

Configurable attributes

Name	Default value	Configurable values
PreferredMethods	{"intern"=>"to_sym"}

Style/StructInheritance

Enabled by default	Supports autocorrection
Enabled	No

This cop checks for inheritance from Struct.new.

Examples

# bad
class Person < Struct.new(:first_name, :last_name)
end

# good
Person = Struct.new(:first_name, :last_name)

References

• https://github.com/rubocop-hq/ruby-style-guide#no-extend-struct-new

Style/SymbolArray

Enabled by default	Supports autocorrection
Enabled	Yes

This cop can check for array literals made up of symbols that are not using the %i() syntax.

Alternatively, it checks for symbol arrays using the %i() syntax on projects which do not want to use that syntax.

Configuration option: MinSize If set, arrays with fewer elements than this value will not trigger the cop. For example, a MinSize of3` will not enforce a style on an array of 2 or fewer elements.

Examples

EnforcedStyle: percent (default)

# good
%i[foo bar baz]

# bad
[:foo, :bar, :baz]

EnforcedStyle: brackets

# good
[:foo, :bar, :baz]

# bad
%i[foo bar baz]

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	percent	percent, brackets
MinSize	2	Integer

References

• https://github.com/rubocop-hq/ruby-style-guide#percent-i

Style/SymbolLiteral

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks symbol literal syntax.

Examples

# bad
:"symbol"

# good
:symbol

Style/SymbolProc

Enabled by default	Supports autocorrection
Enabled	Yes

Use symbols as procs when possible.

Examples

# bad
something.map { |s| s.upcase }

# good
something.map(&:upcase)

Configurable attributes

Name	Default value	Configurable values
IgnoredMethods	respond_to, define_method	Array

Style/TernaryParentheses

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for the presence of parentheses around ternary conditions. It is configurable to enforce inclusion or omission of parentheses using EnforcedStyle. Omission is only enforced when removing the parentheses won't cause a different behavior.

Examples

EnforcedStyle: require_no_parentheses (default)

# bad
foo = (bar?) ? a : b
foo = (bar.baz?) ? a : b
foo = (bar && baz) ? a : b

# good
foo = bar? ? a : b
foo = bar.baz? ? a : b
foo = bar && baz ? a : b

EnforcedStyle: require_parentheses

# bad
foo = bar? ? a : b
foo = bar.baz? ? a : b
foo = bar && baz ? a : b

# good
foo = (bar?) ? a : b
foo = (bar.baz?) ? a : b
foo = (bar && baz) ? a : b

EnforcedStyle: require_parentheses_when_complex

# bad
foo = (bar?) ? a : b
foo = (bar.baz?) ? a : b
foo = bar && baz ? a : b

# good
foo = bar? ? a : b
foo = bar.baz? ? a : b
foo = (bar && baz) ? a : b

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	require_no_parentheses	require_parentheses, require_no_parentheses, require_parentheses_when_complex
AllowSafeAssignment	true	Boolean

Style/TrailingBodyOnClass

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for trailing code after the class definition.

Examples

# bad
class Foo; def foo; end
end

# good
class Foo
  def foo; end
end

Style/TrailingBodyOnMethodDefinition

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for trailing code after the method definition.

Examples

# bad
def some_method; do_stuff
end

def f(x); b = foo
  b[c: x]
end

# good
def some_method
  do_stuff
end

def f(x)
  b = foo
  b[c: x]
end

Style/TrailingBodyOnModule

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for trailing code after the module definition.

Examples

# bad
module Foo extend self
end

# good
module Foo
  extend self
end

Style/TrailingCommaInArguments

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for trailing comma in argument lists.

Examples

EnforcedStyleForMultiline: consistent_comma

# bad
method(1, 2,)

# good
method(
  1, 2,
  3,
)

# good
method(
  1,
  2,
)

EnforcedStyleForMultiline: comma

# bad
method(1, 2,)

# good
method(
  1,
  2,
)

EnforcedStyleForMultiline: no_comma (default)

# bad
method(1, 2,)

# good
method(
  1,
  2
)

Configurable attributes

Name	Default value	Configurable values
EnforcedStyleForMultiline	no_comma	comma, consistent_comma, no_comma

References

• https://github.com/rubocop-hq/ruby-style-guide#no-trailing-params-comma

Style/TrailingCommaInArrayLiteral

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for trailing comma in array literals.

Examples

EnforcedStyleForMultiline: consistent_comma

# bad
a = [1, 2,]

# good
a = [
  1, 2,
  3,
]

# good
a = [
  1,
  2,
]

EnforcedStyleForMultiline: comma

# bad
a = [1, 2,]

# good
a = [
  1,
  2,
]

EnforcedStyleForMultiline: no_comma (default)

# bad
a = [1, 2,]

# good
a = [
  1,
  2
]

Configurable attributes

Name	Default value	Configurable values
EnforcedStyleForMultiline	no_comma	comma, consistent_comma, no_comma

References

• https://github.com/rubocop-hq/ruby-style-guide#no-trailing-array-commas

Style/TrailingCommaInHashLiteral

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for trailing comma in hash literals.

Examples

EnforcedStyleForMultiline: consistent_comma

# bad
a = { foo: 1, bar: 2, }

# good
a = {
  foo: 1, bar: 2,
  qux: 3,
}

# good
a = {
  foo: 1,
  bar: 2,
}

EnforcedStyleForMultiline: comma

# bad
a = { foo: 1, bar: 2, }

# good
a = {
  foo: 1,
  bar: 2,
}

EnforcedStyleForMultiline: no_comma (default)

# bad
a = { foo: 1, bar: 2, }

# good
a = {
  foo: 1,
  bar: 2
}

Configurable attributes

Name	Default value	Configurable values
EnforcedStyleForMultiline	no_comma	comma, consistent_comma, no_comma

Style/TrailingMethodEndStatement

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for trailing code after the method definition.

Examples

# bad
def some_method
do_stuff; end

def do_this(x)
  baz.map { |b| b.this(x) } end

def foo
  block do
    bar
  end end

# good
def some_method
  do_stuff
end

def do_this(x)
  baz.map { |b| b.this(x) }
end

def foo
  block do
    bar
  end
end

Style/TrailingUnderscoreVariable

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for extra underscores in variable assignment.

Examples

# bad
a, b, _ = foo()
a, b, _, = foo()
a, _, _ = foo()
a, _, _, = foo()

# good
a, b, = foo()
a, = foo()
*a, b, _ = foo()
# => We need to know to not include 2 variables in a
a, *b, _ = foo()
# => The correction `a, *b, = foo()` is a syntax error

# good if AllowNamedUnderscoreVariables is true
a, b, _something = foo()

Configurable attributes

Name	Default value	Configurable values
AllowNamedUnderscoreVariables	true	Boolean

Style/TrivialAccessors

Enabled by default	Supports autocorrection
Enabled	Yes

This cop looks for trivial reader/writer methods, that could have been created with the attr_* family of functions automatically.

Examples

# bad
def foo
  @foo
end

def bar=(val)
  @bar = val
end

def self.baz
  @baz
end

# good
attr_reader :foo
attr_writer :bar

class << self
  attr_reader :baz
end

Configurable attributes

Name	Default value	Configurable values
ExactNameMatch	true	Boolean
AllowPredicates	true	Boolean
AllowDSLWriters	false	Boolean
IgnoreClassMethods	false	Boolean
Whitelist	to_ary, to_a, to_c, to_enum, to_h, to_hash, to_i, to_int, to_io, to_open, to_path, to_proc, to_r, to_regexp, to_str, to_s, to_sym	Array

References

• https://github.com/rubocop-hq/ruby-style-guide#attr_family

Style/UnlessElse

Enabled by default	Supports autocorrection
Enabled	Yes

This cop looks for unless expressions with else clauses.

Examples

# bad
unless foo_bar.nil?
  # do something...
else
  # do a different thing...
end

# good
if foo_bar.present?
  # do something...
else
  # do a different thing...
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-else-with-unless

Style/UnneededCapitalW

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for usage of the %W() syntax when %w() would do.

Examples

# bad
%W(cat dog pig)
%W[door wall floor]

# good
%w/swim run bike/
%w[shirt pants shoes]
%W(apple #{fruit} grape)

Style/UnneededCondition

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for unnecessary conditional expressions.

Examples

# bad
a = b ? b : c

# good
a = b || c

# bad
if b
  b
else
  c
end

# good
b || c

# good
if b
  b
elsif cond
  c
end

Style/UnneededInterpolation

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for strings that are just an interpolated expression.

Examples

# bad
"#{@var}"

# good
@var.to_s

# good if @var is already a String
@var

Style/UnneededPercentQ

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for usage of the %q/%Q syntax when '' or "" would do.

Examples

# 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?"'

References

• https://github.com/rubocop-hq/ruby-style-guide#percent-q

Style/UnpackFirst

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for accessing the first element of String#unpack which can be replaced with the shorter method unpack1.

Examples

# bad
'foo'.unpack('h*').first
'foo'.unpack('h*')[0]
'foo'.unpack('h*').slice(0)
'foo'.unpack('h*').at(0)

# good
'foo'.unpack1('h*')

Style/VariableInterpolation

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for variable interpolation (like "#@ivar").

Examples

# bad
"His name is #$name"
/check #$pattern/
"Let's go to the #@store"

# good
"His name is #{$name}"
/check #{$pattern}/
"Let's go to the #{@store}"

References

• https://github.com/rubocop-hq/ruby-style-guide#curlies-interpolate

Style/WhenThen

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for when; uses in case expressions.

Examples

# bad
case foo
when 1; 'baz'
when 2; 'bar'
end

# good
case foo
when 1 then 'baz'
when 2 then 'bar'
end

References

• https://github.com/rubocop-hq/ruby-style-guide#one-line-cases

Style/WhileUntilDo

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for uses of do in multi-line while/until statements.

Examples

# bad
while x.any? do
  do_something(x.pop)
end

# good
while x.any?
  do_something(x.pop)
end

# bad
until x.empty? do
  do_something(x.pop)
end

# good
until x.empty?
  do_something(x.pop)
end

References

• https://github.com/rubocop-hq/ruby-style-guide#no-multiline-while-do

Style/WhileUntilModifier

Enabled by default	Supports autocorrection
Enabled	Yes

Checks for while and until statements that would fit on one line if written as a modifier while/until. The maximum line length is configured in the Metrics/LineLength cop.

Examples

# bad
while x < 10
  x += 1
end

# good
x += 1 while x < 10

# bad
until x > 10
  x += 1
end

# good
x += 1 until x > 10

References

• https://github.com/rubocop-hq/ruby-style-guide#while-as-a-modifier

Style/WordArray

Enabled by default	Supports autocorrection
Enabled	Yes

This cop can check for array literals made up of word-like strings, that are not using the %w() syntax.

Alternatively, it can check for uses of the %w() syntax, in projects which do not want to include that syntax.

Configuration option: MinSize If set, arrays with fewer elements than this value will not trigger the cop. For example, a MinSize of 3 will not enforce a style on an array of 2 or fewer elements.

Examples

EnforcedStyle: percent (default)

# good
%w[foo bar baz]

# bad
['foo', 'bar', 'baz']

EnforcedStyle: brackets

# good
['foo', 'bar', 'baz']

# bad
%w[foo bar baz]

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	percent	percent, brackets
MinSize	2	Integer
WordRegex	(?-mix:\A[\p{Word}\n\t]+\z)

References

• https://github.com/rubocop-hq/ruby-style-guide#percent-w

Style/YodaCondition

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for Yoda conditions, i.e. comparison operations where readability is reduced because the operands are not ordered the same way as they would be ordered in spoken English.

Examples

EnforcedStyle: all_comparison_operators (default)

# bad
99 == foo
"bar" != foo
42 >= foo
10 < bar

# good
foo == 99
foo == "bar"
foo <= 42
bar > 10

EnforcedStyle: equality_operators_only

# bad
99 == foo
"bar" != foo

# good
99 >= foo
3 < a && a < 5

Configurable attributes

Name	Default value	Configurable values
EnforcedStyle	all_comparison_operators	all_comparison_operators, equality_operators_only

References

• https://en.wikipedia.org/wiki/Yoda_conditions

Style/ZeroLengthPredicate

Enabled by default	Supports autocorrection
Enabled	Yes

This cop checks for numeric comparisons that can be replaced by a predicate method, such as receiver.length == 0, receiver.length > 0, receiver.length != 0, receiver.length < 1 and receiver.size == 0 that can be replaced by receiver.empty? and !receiver.empty.

Examples

# bad
[1, 2, 3].length == 0
0 == "foobar".length
array.length < 1
{a: 1, b: 2}.length != 0
string.length > 0
hash.size > 0

# good
[1, 2, 3].empty?
"foobar".empty?
array.empty?
!{a: 1, b: 2}.empty?
!string.empty?
!hash.empty?