Style

Style/AccessModifierDeclarations

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.57 0.81

Access modifiers should be declared to apply to a group of methods or inline before each method, depending on configuration. EnforcedStyle config covers only method definitions. Applications of visibility methods to symbols can be controlled using AllowModifiersOnSymbols config.

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

AllowModifiersOnSymbols: true

# good
class Foo

  private :bar, :baz

end

AllowModifiersOnSymbols: false

# bad
class Foo

  private :bar, :baz

end

Configurable attributes

Name Default value Configurable values
EnforcedStyle group inline, group
AllowModifiersOnSymbols true Boolean

Style/Alias

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.36

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

Style/AndOr

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.25

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

Style/ArrayJoin

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.20 0.31

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

Style/AsciiComments

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.9 0.52

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

Style/Attr

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.12

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

Style/AutoResourceCleanup

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.30 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.25 -

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

Style/BeginBlock

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.9 -

This cop checks for BEGIN blocks.

Examples

# bad
BEGIN { test }

References

Style/BlockComments

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.23

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

Examples

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

# good
# Multiple lines
# of comments...

References

Style/BlockDelimiters

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.30 0.35

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

# The AllowBracesOnProceduralOneLiners option is ignored unless the
# EnforcedStyle is set to `semantic`. If so:

# If the AllowBracesOnProceduralOneLiners option is unspecified, or
# set to `false` or any other falsey value, then semantic purity is
# maintained, so one-line procedural blocks must use do-end, not
# braces.

# bad
collection.each { |element| puts element }

# good
collection.each do |element| puts element end

# If the AllowBracesOnProceduralOneLiners option is set to `true`, or
# any other truthy value, then one-line procedural blocks may use
# either style. (There is no setting for requiring braces on them.)

# good
collection.each { |element| puts element }

# also good
collection.each do |element| puts element end

EnforcedStyle: braces_for_chaining

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

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

EnforcedStyle: always_braces

# bad
words.each do |word|
  word.flip.flop
end

# good
words.each { |word|
  word.flip.flop
}

BracesRequiredMethods: ['sig']

# Methods listed in the BracesRequiredMethods list, such as 'sig'
# in this example, will require `{...}` braces. This option takes
# precedence over all other configurations except IgnoredMethods.

# bad
sig do
  params(
    foo: string,
  ).void
end
def bar(foo)
  puts foo
end

# good
sig {
  params(
    foo: string,
  ).void
}
def bar(foo)
  puts foo
end

Configurable attributes

Name Default value Configurable values
EnforcedStyle line_count_based line_count_based, semantic, braces_for_chaining, always_braces
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
AllowBracesOnProceduralOneLiners false Boolean
BracesRequiredMethods [] Array

References

Style/CaseEquality

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.9 -

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

Style/CharacterLiteral

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 -

Checks for uses of the character literal ?x.

Examples

# bad
?x

# good
'x'

# good
?\C-\M-d

References

Style/ClassAndModuleChildren

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes (Unsafe) 0.19 -

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

Style/ClassCheck

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.24 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.20

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

Style/ClassVars

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.13 -

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

Style/CollectionMethods

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled No Yes (Unsafe) 0.9 0.27

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.

You can customize the mapping from undesired method to desired method.

e.g. to use detect over find:

Style/CollectionMethods: PreferredMethods: find: detect

The default mapping for PreferredMethods behaves as follows.

Examples

# bad
items.collect
items.collect!
items.inject
items.detect
items.find_all
items.member?

# good
items.map
items.map!
items.reduce
items.find
items.select
items.include?

Configurable attributes

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

References

Style/ColonMethodCall

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 -

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

Style/ColonMethodDefinition

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.52 -

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

Style/CommandLiteral

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.30 -

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

Style/CommentAnnotation

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.10 0.31

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

Style/CommentedKeyword

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.51 -

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 (:nodoc:, :yields:, rubocop:disable and rubocop:todo) 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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.36 0.47

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/ConstantVisibility

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.66 -

This cop checks that constants defined in classes and modules have an explicit visibility declaration. By default, Ruby makes all class- and module constants public, which litters the public API of the class or module. Explicitly declaring a visibility makes intent more clear, and prevents outside actors from touching private state.

Examples

# bad
class Foo
  BAR = 42
  BAZ = 43
end

# good
class Foo
  BAR = 42
  private_constant :BAR

  BAZ = 43
  public_constant :BAZ
end

Style/Copyright

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes Yes 0.30 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.51 0.59

This cop checks for consistent usage of the DateTime class over the Time class. This cop is disabled by default since these classes, although highly overlapping, have particularities that make them not replaceable in certain situations when dealing with multiple timezones and/or DST.

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 `Time` for modern date
Time.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

Style/DefWithParentheses

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.12

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

Style/Dir

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.50 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.9 -

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, constant definitions or constant visibility declarations.

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

module Math
end

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

# allowed
  # Class without body
  class Person
  end

  # Namespace - A namespace can be a class or a module
  # Containing a class
  module Namespace
    # Description/Explanation of Person class
    class Person
      # ...
    end
  end

  # Containing constant visibility declaration
  module Namespace
    class Private
    end

    private_constant :Private
  end

  # Containing constant definition
  module Namespace
    Public = Class.new
  end

Configurable attributes

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

Style/DocumentationMethod

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.43 -

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

RequireForNonPublicMethods: false (default)

# good
class Foo
  protected
  def do_something
  end
end

class Foo
  private
  def do_something
  end
end

RequireForNonPublicMethods: true

# bad
class Foo
  protected
  def do_something
  end
end

class Foo
  private
  def do_something
  end
end

# good
class Foo
  protected
  # Documentation
  def do_something
  end
end

class Foo
  private
  # Documentation
  def do_something
  end
end

Configurable attributes

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

Style/DoubleCopDisableDirective

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.73 -

Detects double disable comments on one line. This is mostly to catch automatically generated comments that need to be regenerated.

Examples

# bad
def f # rubocop:disable Style/For # rubocop:disable Metrics/AbcSize
end

# good
# rubocop:disable Metrics/AbcSize
def f # rubocop:disable Style/For
end
# rubocop:enable Metrics/AbcSize

# if both fit on one line
def f # rubocop:disable Style/For, Metrics/AbcSize
end

Style/DoubleNegation

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.19 -

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

Style/EachForSimpleLoop

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.41 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.22 0.42

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.52 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.40 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.28 0.32

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.52 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.12

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

Style/EmptyMethod

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.46 -

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

Style/Encoding

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.50

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

Examples

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

References

Style/EndBlock

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.81

This cop checks for END blocks.

Examples

# bad
END { puts 'Goodbye!' }

# good
at_exit { puts 'Goodbye!' }

References

Style/EvalWithLocation

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.52 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.12 0.29

This cop checks for places where Integer#even? or Integer#odd? can be used.

Examples

# bad
if x % 2 == 0
end

# good
if x.even?
end

References

Style/ExpandPathArguments

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.53 -

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/FloatDivision

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.72 -

This cop checks for division with integers coerced to floats. It is recommended to either always use fdiv or coerce one side only. This cop also provides other options for code consistency.

Examples

EnforcedStyle: single_coerce (default)

# bad
a.to_f / b.to_f

# good
a.to_f / b
a / b.to_f

EnforcedStyle: left_coerce

# bad
a / b.to_f
a.to_f / b.to_f

# good
a.to_f / b

EnforcedStyle: right_coerce

# bad
a.to_f / b
a.to_f / b.to_f

# good
a / b.to_f

EnforcedStyle: fdiv

# bad
a / b.to_f
a.to_f / b
a.to_f / b.to_f

# good
a.fdiv(b)

Configurable attributes

Name Default value Configurable values
EnforcedStyle single_coerce left_coerce, right_coerce, single_coerce, fdiv

References

Style/For

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.13 0.59

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.

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

Style/FormatString

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.19 0.49

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

Style/FormatStringToken

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.49 0.75

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: printf, 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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled No Yes (Unsafe) 0.36 0.79

This cop is designed to help you transition from mutable string literals to frozen string literals. 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 future Ruby. The comment will be added below a shebang and encoding comment. The frozen string literal comment is only valid in Ruby 2.3+.

Note that the cop will ignore files where the comment exists but is set to false instead of true.

Examples

EnforcedStyle: always (default)

# 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

# good
# frozen_string_literal: false

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

EnforcedStyle: always_true

# The `always_true` style enforces that the frozen string literal
# comment is set to `true`. This is a stricter option than `always`
# and forces projects to use frozen string literals.
# bad
# frozen_string_literal: false

module Baz
  # ...
end

# bad
module Baz
  # ...
end

# good
# frozen_string_literal: true

module Bar
  # ...
end

Configurable attributes

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

Style/GlobalVars

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.13 -

This cop 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

Style/GuardClause

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.20 0.22

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

Style/HashEachMethods

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Pending No Yes (Unsafe) 0.80 -

This cop checks for uses of each_key and each_value Hash methods.

Note: If you have an array of two-element arrays, you can put parentheses around the block arguments to indicate that you're not working with a hash, and suppress RuboCop offenses.

Examples

# bad
hash.keys.each { |k| p k }
hash.values.each { |v| p v }

# good
hash.each_key { |k| p k }
hash.each_value { |v| p v }

References

Style/HashSyntax

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.43

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

Style/HashTransformKeys

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Pending No Yes (Unsafe) 0.80 -

This cop looks for uses of _.each_with_object({}) {...}, _.map {...}.to_h, and Hash[_.map {...}] that are actually just transforming the keys of a hash, and tries to use a simpler & faster call to transform_keys instead.

This can produce false positives if we are transforming an enumerable of key-value-like pairs that isn't actually a hash, e.g.: [[k1, v1], [k2, v2], ...]

This cop should only be enabled on Ruby version 2.5 or newer (transform_keys was added in Ruby 2.5.)

Examples

# bad
{a: 1, b: 2}.each_with_object({}) { |(k, v), h| h[foo(k)] = v }
{a: 1, b: 2}.map { |k, v| [k.to_s, v] }

# good
{a: 1, b: 2}.transform_keys { |k| foo(k) }
{a: 1, b: 2}.transform_keys { |k| k.to_s }

Style/HashTransformValues

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Pending No Yes (Unsafe) 0.80 -

This cop looks for uses of _.each_with_object({}) {...}, _.map {...}.to_h, and Hash[_.map {...}] that are actually just transforming the values of a hash, and tries to use a simpler & faster call to transform_values instead.

This can produce false positives if we are transforming an enumerable of key-value-like pairs that isn't actually a hash, e.g.: [[k1, v1], [k2, v2], ...]

This cop should only be enabled on Ruby version 2.4 or newer (transform_values was added in Ruby 2.4.)

Examples

# bad
{a: 1, b: 2}.each_with_object({}) { |(k, v), h| h[k] = foo(v) }
{a: 1, b: 2}.map { |k, v| [k, v * v] }

# good
{a: 1, b: 2}.transform_values { |v| foo(v) }
{a: 1, b: 2}.transform_values { |v| v * v }

Style/IdenticalConditionalBranches

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.36 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.36 -

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

AllowIfModifier: false (default)

# bad
if condition_a
  action_a
else
  action_b if condition_b
end

# good
if condition_a
  action_a
elsif condition_b
  action_b
end

AllowIfModifier: true

# good
if condition_a
  action_a
else
  action_b if condition_b
end

# good
if condition_a
  action_a
elsif condition_b
  action_b
end

Configurable attributes

Name Default value Configurable values
AllowIfModifier false Boolean

Style/IfUnlessModifier

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.30

Checks for if and unless statements that would fit on one line if written as modifier if/unless. The cop also checks for modifier if/unless lines that exceed the maximum line length.

The maximum line length is configured in the Layout/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

do_something_in_a_method_with_a_long_name(arg) if long_condition

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

if long_condition
  do_something_in_a_method_with_a_long_name(arg)
end

References

Style/IfUnlessModifierOfIfUnless

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.39 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.9 -

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

Style/ImplicitRuntimeError

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.41 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.26 0.61

Use Kernel#loop for infinite loops.

Examples

# bad
while true
  work
end

# good
loop do
  work
end

References

Style/InlineComment

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.23 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled No Yes (Unsafe) 0.48 -

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
# Blocks with guard clauses are ignored:
foo.select do |f|
  next if f.zero?
  f != 1
end

Configurable attributes

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

Style/IpAddresses

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.58 0.77

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
AllowedAddresses :: Array

Style/Lambda

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.40

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

Style/LambdaCall

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.13 0.14

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

Style/LineEndConcatenation

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes (Unsafe) 0.18 0.64

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 Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes Yes 0.47 0.61

This cop enforces the presence (default) or absence of parentheses in method calls containing parameters.

In the default style (require_parentheses), macro methods are ignored. Additional methods can be added to the IgnoredMethods or IgnoredPatterns list. These options are valid only in the default style. Macros can be included by either setting IgnoreMacros to false or adding specific macros to the IncludedMacros list.

Precedence of options is all follows:

  1. IgnoredMethods
  2. IgnoredPatterns
  3. IncludedMacros

eg. If a method is listed in both IncludedMacros and IgnoredMethods, then the latter takes precedence (that is, the method is ignored).

In the alternative style (omit_parentheses), there are three additional options.

  1. AllowParenthesesInChaining is false by default. Setting it to true allows the presence of parentheses in the last call during method chaining.

  2. AllowParenthesesInMultilineCall is false by default. Setting it to true allows the presence of parentheses in multi-line method calls.

  3. AllowParenthesesInCamelCaseMethod is false by default. This allows the presence of parentheses when calling a method whose name begins with a capital letter and which has no arguments. Setting it to true allows the presence of parentheses in such a method call even with arguments.

Examples

EnforcedStyle: require_parentheses (default)

# 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'

# okay with `^assert` listed in `IgnoredPatterns`
assert_equal 'test', x

EnforcedStyle: omit_parentheses

# bad
array.delete(e)

# good
array.delete e

# bad
foo.enforce(strict: true)

# good
foo.enforce strict: true

IgnoreMacros: true (default)

# good
class Foo
  bar :baz
end

IgnoreMacros: false

# bad
class Foo
  bar :baz
end

AllowParenthesesInMultilineCall: false (default)

# bad
foo.enforce(
  strict: true
)

# good
foo.enforce \
  strict: true

AllowParenthesesInMultilineCall: true

# good
foo.enforce(
  strict: true
)

# good
foo.enforce \
  strict: true

AllowParenthesesInChaining: false (default)

# bad
foo().bar(1)

# good
foo().bar 1

AllowParenthesesInChaining: true

# good
foo().bar(1)

# good
foo().bar 1

AllowParenthesesInCamelCaseMethod: false (default)

# bad
Array(1)

# good
Array 1

AllowParenthesesInCamelCaseMethod: true

# good
Array(1)

# good
Array 1

Configurable attributes

Name Default value Configurable values
IgnoreMacros true Boolean
IgnoredMethods [] Array
IgnoredPatterns [] Array
IncludedMacros [] Array
AllowParenthesesInMultilineCall false Boolean
AllowParenthesesInChaining false Boolean
AllowParenthesesInCamelCaseMethod false Boolean
EnforcedStyle require_parentheses require_parentheses, omit_parentheses

References

Style/MethodCallWithoutArgsParentheses

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.47 0.55

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

Style/MethodCalledOnDoEndBlock

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.14 -

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

Style/MethodDefParentheses

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.16 0.35

This cop 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

Style/MethodMissingSuper

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.56 -

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

Style/MinMax

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.50 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.30 0.38

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.56 -

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

Style/MixinGrouping

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.48 0.49

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

Style/MixinUsage

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.51 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes (Unsafe) 0.11 0.65

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

Supported styles are: module_function, extend_self, forbidden.

In case there are private methods, the cop won't be activated. Otherwise, it forces to change the flow of the default code.

The option forbidden prohibits the usage of both styles.

These offenses are not safe to auto-correct 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: module_function (default)

# good
module Test
  extend self
  # ...
  private
  # ...
end

EnforcedStyle: extend_self

# bad
module Test
  module_function
  # ...
end

# good
module Test
  extend self
  # ...
end

EnforcedStyle: forbidden

# bad
module Test
  module_function
  # ...
end

# bad
module Test
  extend self
  # ...
end

# bad
module Test
  extend self
  # ...
  private
  # ...
end

Configurable attributes

Name Default value Configurable values
EnforcedStyle module_function module_function, extend_self, forbidden
Autocorrect false Boolean

References

Style/MultilineBlockChain

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.13 -

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

Style/MultilineIfModifier

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.45 -

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

Style/MultilineIfThen

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.26

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

Style/MultilineMemoization

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.44 0.48

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/MultilineMethodSignature

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.59 -

This cop checks for method signatures that span multiple lines.

Examples

# good

def foo(bar, baz)
end

# bad

def foo(bar,
        baz)
end

Style/MultilineTernaryOperator

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.9 -

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

Style/MultilineWhenThen

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.73 -

This cop checks uses of the then keyword in multi-line when statements.

Examples

# bad
case foo
when bar then
end

# good
case foo
when bar
end

# good
case foo
when bar then do_something
end

References

Style/MultipleComparison

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.49 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.34 0.65

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

Strict mode can be used to freeze all constants, rather than just literals. Strict mode is considered an experimental feature. It has not been updated with an exhaustive list of all methods that will produce frozen objects so there is a decent chance of getting some false positives. Luckily, there is no harm in freezing an already frozen object.

Examples

EnforcedStyle: literals (default)

# bad
CONST = [1, 2, 3]

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

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

# good
CONST = Something.new

EnforcedStyle: strict

# bad
CONST = Something.new

# bad
CONST = Struct.new do
  def foo
    puts 1
  end
end

# good
CONST = Something.new.freeze

# good
CONST = Struct.new do
  def foo
    puts 1
  end
end.freeze

Configurable attributes

Name Default value Configurable values
EnforcedStyle literals literals, strict

Style/NegatedIf

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.20 0.48

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

Style/NegatedUnless

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.69 -

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

  • both
  • prefix
  • postfix

Examples

EnforcedStyle: both (default)

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

# bad
unless !foo
  bar
end

# good
if foo
  bar
end

# bad
bar unless !foo

# good
bar if foo

EnforcedStyle: prefix

# enforces `if` for just `prefix` conditionals

# bad
unless !foo
  bar
end

# good
if foo
  bar
end

# good
bar unless !foo

EnforcedStyle: postfix

# enforces `if` for just `postfix` conditionals

# bad
bar unless !foo

# good
bar if foo

# good
unless !foo
  bar
end

Configurable attributes

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

References

Style/NegatedWhile

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.20 -

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

Style/NestedModifier

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.35 -

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

Style/NestedParenthesizedCalls

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.36 0.77

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

Examples

# good
method1(method2(arg))

# bad
method1(method2 arg)

Configurable attributes

Name Default value Configurable values
AllowedMethods 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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.9 -

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

Style/Next

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.22 0.35

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 |a|
  puts a if a == 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| puts a if a == 1 }`

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

Style/NilComparison

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.12 0.59

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

Style/NonNilCheck

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.20 0.22

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

With IncludeSemanticChanges set to false by default, this cop does not report offenses for !x.nil? and does no changes that might change behavior.

With IncludeSemanticChanges set to true, this cop reports offenses for !x.nil? and autocorrects that and x != nil to solely x, which is usually OK, but might change behavior.

Examples

# bad
if x != nil
end

# good
if x
end

# Non-nil checks are allowed if they are the final nodes of predicate.
# good
def signed_in?
  !current_user.nil?
end

IncludeSemanticChanges: false (default)

# good
if !x.nil?
end

IncludeSemanticChanges: true

# bad
if !x.nil?
end

Configurable attributes

Name Default value Configurable values
IncludeSemanticChanges false Boolean

References

Style/Not

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.20

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

Style/NumericLiteralPrefix

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.41 -

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

Style/NumericLiterals

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.48

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

Strict: false (default)

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

Strict: true

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

Configurable attributes

Name Default value Configurable values
MinDigits 5 Integer
Strict false Boolean

References

Style/NumericPredicate

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled No Yes (Unsafe) 0.42 0.59

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

Style/OneLineConditional

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.38

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

Style/OptionHash

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.33 0.34

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.33 -

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

Style/OrAssignment

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.50 -

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

Style/ParallelAssignment

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.32 -

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

Style/ParenthesesAroundCondition

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.56

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

AllowSafeAssignment option for safe assignment. By safe assignment we mean putting parentheses around an assignment to indicate "I know I'm using an assignment as a condition. It's not a mistake."

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

AllowSafeAssignment: true (default)

# good
foo unless (bar = baz)

AllowSafeAssignment: false

# bad
foo unless (bar = baz)

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

Style/PercentLiteralDelimiters

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.19 0.48.1

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

Style/PercentQLiterals

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.25 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.13 -

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

Style/PreferredHashMethods

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled No Yes (Unsafe) 0.41 0.70

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

Style/Proc

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.18

This cop 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

Style/RaiseArgs

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.14 0.40

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

Style/RandomWithOffset

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.52 -

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

Style/RedundantBegin

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.10 0.21

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

Style/RedundantCapitalW

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.76 -

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/RedundantCondition

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.76 -

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/RedundantConditional

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.50 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.14 0.29

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

Style/RedundantFreeze

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.34 0.66

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

Examples

# bad
CONST = 1.freeze

# good
CONST = 1

Style/RedundantInterpolation

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.76 -

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/RedundantParentheses

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.36 -

This cop checks for redundant parentheses.

Examples

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

# good
x if y.z.nil?

Style/RedundantPercentQ

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.76 -

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

Style/RedundantReturn

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.10 0.14

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

AllowMultipleReturnValues: false (default)

# bad
def test
  return x, y
end

AllowMultipleReturnValues: true

# good
def test
  return x, y
end

Configurable attributes

Name Default value Configurable values
AllowMultipleReturnValues false Boolean

References

Style/RedundantSelf

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.10 0.13

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

Style/RedundantSort

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.76 -

This cop is used to identify instances of sorting and then taking only the first or last element. The same behavior can be accomplished without a relatively expensive sort by using Enumerable#min instead of sorting and taking the first element and Enumerable#max instead of sorting and taking the last element. Similarly, Enumerable#min_by and Enumerable#max_by can replace Enumerable#sort_by calls after which only the first or last element is used.

Examples

# bad
[2, 1, 3].sort.first
[2, 1, 3].sort[0]
[2, 1, 3].sort.at(0)
[2, 1, 3].sort.slice(0)

# good
[2, 1, 3].min

# bad
[2, 1, 3].sort.last
[2, 1, 3].sort[-1]
[2, 1, 3].sort.at(-1)
[2, 1, 3].sort.slice(-1)

# good
[2, 1, 3].max

# bad
arr.sort_by(&:foo).first
arr.sort_by(&:foo)[0]
arr.sort_by(&:foo).at(0)
arr.sort_by(&:foo).slice(0)

# good
arr.min_by(&:foo)

# bad
arr.sort_by(&:foo).last
arr.sort_by(&:foo)[-1]
arr.sort_by(&:foo).at(-1)
arr.sort_by(&:foo).slice(-1)

# good
arr.max_by(&:foo)

Style/RedundantSortBy

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.36 -

This cop identifies places where sort_by { ... } can be replaced by sort.

Examples

# bad
array.sort_by { |x| x }
array.sort_by do |var|
  var
end

# good
array.sort

Style/RegexpLiteral

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.30

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

Style/RescueModifier

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.34

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

The cop to check rescue in its modifier form is added for following reasons:

  • The syntax of modifier form rescue can be misleading because it might led us to believe that rescue handles the given exception but it actually rescue all exceptions to return the given rescue block. In this case, value returned by handle_error or SomeException.

  • Modifier form rescue would rescue all the exceptions. It would silently skip all exception or errors and handle the error. Example: If NoMethodError is raised, modifier form rescue would handle the exception.

Examples

# bad
some_method rescue handle_error

# bad
some_method rescue SomeException

# good
begin
  some_method
rescue
  handle_error
end

# good
begin
  some_method
rescue SomeException
  handle_error
end

References

Style/RescueStandardError

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.52 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes Yes 0.50 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.43 0.77

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
AllowedMethods present?, blank?, presence, try, try! Array

Style/Sample

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.30 -

This cop is used to identify usages of shuffle.first, shuffle.last, and shuffle[] and change them to use sample instead.

Examples

# bad
[1, 2, 3].shuffle.first
[1, 2, 3].shuffle.first(2)
[1, 2, 3].shuffle.last
[2, 1, 3].shuffle.at(0)
[2, 1, 3].shuffle.slice(0)
[1, 2, 3].shuffle[2]
[1, 2, 3].shuffle[0, 2]    # sample(2) will do the same
[1, 2, 3].shuffle[0..2]    # sample(3) will do the same
[1, 2, 3].shuffle(random: Random.new).first

# good
[1, 2, 3].shuffle
[1, 2, 3].sample
[1, 2, 3].sample(3)
[1, 2, 3].shuffle[1, 3]    # sample(3) might return a longer Array
[1, 2, 3].shuffle[1..3]    # sample(3) might return a longer Array
[1, 2, 3].shuffle[foo, bar]
[1, 2, 3].shuffle(random: Random.new)

References

Style/SelfAssignment

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.19 0.29

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

Examples

# bad
x = x + 1

# good
x += 1

References

Style/Semicolon

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.19

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

This cop has AllowAsExpressionSeparator configuration option. It allows ; to separate several expressions on the same line.

Examples

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

# good
foo = 1
bar = 2
baz = 3

AllowAsExpressionSeparator: false (default)

# bad
foo = 1; bar = 2

AllowAsExpressionSeparator: true

# good
foo = 1; bar = 2

Configurable attributes

Name Default value Configurable values
AllowAsExpressionSeparator false Boolean

References

Style/Send

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.33 -

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

Style/SignalException

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.11 0.37

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

Style/SingleLineBlockParams

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes No 0.16 0.47

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.19

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

AllowIfMethodIsEmpty: true (default)

# good
def no_op; end

AllowIfMethodIsEmpty: false

# bad
def no_op; end

Configurable attributes

Name Default value Configurable values
AllowIfMethodIsEmpty true Boolean

References

Style/SpecialGlobalVars

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes (Unsafe) 0.13 0.36

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 [email protected]
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

Style/StabbyLambdaParentheses

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.35 -

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

Style/StderrPuts

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.51 -

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

Examples

# bad
$stderr.puts('hello')

# good
warn('hello')

References

Style/StringHashKeys

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled No Yes (Unsafe) 0.52 0.75

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

Style/StringLiterals

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.36

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

Style/StringLiteralsInInterpolation

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.27 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Disabled Yes Yes 0.34 0.34.2

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/Strip

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.36 -

This cop identifies places where lstrip.rstrip can be replaced by strip.

Examples

# bad
'abc'.lstrip.rstrip
'abc'.rstrip.lstrip

# good
'abc'.strip

Style/StructInheritance

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes No 0.29 -

This cop checks for inheritance from Struct.new.

Examples

# bad
class Person < Struct.new(:first_name, :last_name)
  def age
    42
  end
end

# good
Person = Struct.new(:first_name, :last_name) do
  def age
    42
  end
end

References

Style/SymbolArray

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.49

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 of 3 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

Style/SymbolLiteral

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.30 -

This cop checks symbol literal syntax.

Examples

# bad
:"symbol"

# good
:symbol

Style/SymbolProc

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes (Unsafe) 0.26 0.64

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.42 0.46

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.

AllowSafeAssignment option for safe assignment. By safe assignment we mean putting parentheses around an assignment to indicate "I know I'm using an assignment as a condition. It's not a mistake."

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

AllowSafeAssignment: true (default)

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

AllowSafeAssignment: false

# bad
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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.53 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.52 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.53 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.36 -

This cop checks for trailing comma in argument lists. The supported styles are:

  • consistent_comma: Requires a comma after the last argument, for all parenthesized method calls with arguments.
  • comma: Requires a comma after the last argument, but only for parenthesized method calls where each argument is on its own line.
  • no_comma: Does not requires a comma after the last argument.

Examples

EnforcedStyleForMultiline: consistent_comma

# bad
method(1, 2,)

# good
method(1, 2)

# good
method(
  1, 2,
  3,
)

# good
method(
  1, 2, 3,
)

# good
method(
  1,
  2,
)

EnforcedStyleForMultiline: comma

# bad
method(1, 2,)

# good
method(1, 2)

# bad
method(
  1, 2,
  3,
)

# good
method(
  1, 2,
  3
)

# bad
method(
  1, 2, 3,
)

# good
method(
  1, 2, 3
)

# good
method(
  1,
  2,
)

EnforcedStyleForMultiline: no_comma (default)

# bad
method(1, 2,)

# good
method(1, 2)

# good
method(
  1,
  2
)

Configurable attributes

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

References

Style/TrailingCommaInArrayLiteral

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.53 -

This cop checks for trailing comma in array literals. The configuration options are:

  • consistent_comma: Requires a comma after the last item of all non-empty, multiline array literals.
  • comma: Requires a comma after last item in an array, but only when each item is on its own line.
  • no_comma: Does not requires a comma after the last item in an array

Examples

EnforcedStyleForMultiline: consistent_comma

# bad
a = [1, 2,]

# good
a = [1, 2]

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

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

# good
a = [
  1,
  2,
]

EnforcedStyleForMultiline: comma

# bad
a = [1, 2,]

# good
a = [1, 2]

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

# good
a = [
  1, 2,
  3
]

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

# good
a = [
  1, 2, 3
]

# 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

Style/TrailingCommaInBlockArgs

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Disabled No Yes (Unsafe) 0.81 -

This cop checks whether trailing commas in block arguments are required. Blocks with only one argument and a trailing comma require that comma to be present. Blocks with more than one argument never require a trailing comma.

add do |foo, bar,| foo + bar end

# good add do |foo, bar| foo + bar end

# good add do |foo,| foo end

# good add do foo + bar end

Examples

# bad
add { |foo, bar,| foo + bar }

 # good
add { |foo, bar| foo + bar }

# good
add { |foo,| foo }

# good
add { foo }

# bad

Style/TrailingCommaInHashLiteral

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.53 -

This cop checks for trailing comma in hash literals. The configuration options are:

  • consistent_comma: Requires a comma after the last item of all non-empty, multiline hash literals.
  • comma: Requires a comma after the last item in a hash, but only when each item is on its own line.
  • no_comma: Does not requires a comma after the last item in a hash

Examples

EnforcedStyleForMultiline: consistent_comma

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

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

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

# 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 }

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

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

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

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

# 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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.52 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.31 0.35

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

AllowNamedUnderscoreVariables: true (default)

# good
a, b, _something = foo()

AllowNamedUnderscoreVariables: false

# bad
a, b, _something = foo()

Configurable attributes

Name Default value Configurable values
AllowNamedUnderscoreVariables true Boolean

Style/TrivialAccessors

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.77

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
AllowedMethods 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

Style/UnlessElse

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 -

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

Style/UnpackFirst

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.54 -

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 Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.20

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

Style/WhenThen

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 -

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

Style/WhileUntilDo

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 -

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

Style/WhileUntilModifier

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.30

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 Layout/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

Style/WordArray

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled Yes Yes 0.9 0.36

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}|\p{Word}-\p{Word}|\n|\t)+\z)

References

Style/YodaCondition

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled No Yes (Unsafe) 0.49 0.75

This cop can either enforce or forbid Yoda conditions, i.e. comparison operations where the order of expression is reversed. eg. 5 == x

Examples

EnforcedStyle: forbid_for_all_comparison_operators (default)

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

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

EnforcedStyle: forbid_for_equality_operators_only

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

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

EnforcedStyle: require_for_all_comparison_operators

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

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

EnforcedStyle: require_for_equality_operators_only

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

# good
99 == foo
"bar" != foo

Configurable attributes

Name Default value Configurable values
EnforcedStyle forbid_for_all_comparison_operators forbid_for_all_comparison_operators, forbid_for_equality_operators_only, require_for_all_comparison_operators, require_for_equality_operators_only

References

Style/ZeroLengthPredicate

Enabled by default Safe Supports autocorrection VersionAdded VersionChanged
Enabled No Yes (Unsafe) 0.37 0.39

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?