This cop checks for places where keyword arguments can be used instead of boolean arguments when defining methods. respond_to_missing? method is allowed by default. These are customizable with AllowedMethods option.

Example:

# bad
def some_method(bar = false)
  puts bar
end

# bad - common hack before keyword args were introduced
def some_method(options = {})
  bar = options.fetch(:bar, false)
  puts bar
end

# good
def some_method(bar: false)
  puts bar
end

Example: AllowedMethods: ['some_method']

# good
def some_method(bar = false)
  puts bar
end

This cop enforces the use of Object#instance_of? instead of class comparison for equality.

Example:

# bad
var.class == Date
var.class.equal?(Date)
var.class.eql?(Date)
var.class.name == 'Date'

# good
var.instance_of?(Date)

This cop checks for redundant begin blocks.

Currently it checks for code like this:

Example:

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

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

# bad
begin
  do_something
end

# good
do_something

# 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

This cop checks whether comments have a leading space after the # denoting the start of the comment. The leading space is not required for some RDoc special syntax, like #++, #--, #:nodoc, =begin- and =end comments, "shebang" directives, or rackup options.

Example:

# bad
#Some comment

# good
# Some comment

Example: AllowDoxygenCommentStyle: false (default)

# bad

#**
# Some comment
# Another line of comment
#*

Example: AllowDoxygenCommentStyle: true

# good

#**
# Some comment
# Another line of comment
#*

Example: AllowGemfileRubyComment: false (default)

# bad

#ruby=2.7.0
#ruby-gemset=myproject

Example: AllowGemfileRubyComment: true

# good

#ruby=2.7.0
#ruby-gemset=myproject

Single Line Per Selector

Rule single-line-per-selector will enforce whether selectors should be placed on a new line.

Examples

When enabled, the following are allowed:

.foo,
.bar {
  content: 'baz';
}

When enabled, the following are disallowed:

.foo, .bar {
  content: 'baz';
}

Single Line Per Selector

Rule single-line-per-selector will enforce whether selectors should be placed on a new line.

Examples

When enabled, the following are allowed:

.foo,
.bar {
  content: 'baz';
}

When enabled, the following are disallowed:

.foo, .bar {
  content: 'baz';
}

Single Line Per Selector

Rule single-line-per-selector will enforce whether selectors should be placed on a new line.

Examples

When enabled, the following are allowed:

.foo,
.bar {
  content: 'baz';
}

When enabled, the following are disallowed:

.foo, .bar {
  content: 'baz';
}

Single Line Per Selector

Rule single-line-per-selector will enforce whether selectors should be placed on a new line.

Examples

When enabled, the following are allowed:

.foo,
.bar {
  content: 'baz';
}

When enabled, the following are disallowed:

.foo, .bar {
  content: 'baz';
}

This cop checks for places where multiple consecutive loops over the same data can be combined into a single loop. It is very likely that combining them will make the code more efficient and more concise.

It is marked as unsafe, because the first loop might modify a state that the second loop depends on; these two aren't combinable.

Example:

# bad
def method
  items.each do |item|
    do_something(item)
  end

  items.each do |item|
    do_something_else(item)
  end
end

# good
def method
  items.each do |item|
    do_something(item)
    do_something_else(item)
  end
end

# bad
def method
  for item in items do
    do_something(item)
  end

  for item in items do
    do_something_else(item)
  end
end

# good
def method
  for item in items do
    do_something(item)
    do_something_else(item)
  end
end

# good
def method
  each_slice(2) { |slice| do_something(slice) }
  each_slice(3) { |slice| do_something(slice) }
end

This cop checks for redundant begin blocks.

Currently it checks for code like this:

Example:

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

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

# bad
begin
  do_something
end

# good
do_something

# 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

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
• nomixedkeys - simply checks for hashes with mixed syntaxes
• ruby19nomixed_keys - forces use of ruby 1.9 syntax and forbids mixed syntax hashes

Example: 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

Example: EnforcedStyle: hash_rockets

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

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

Example: EnforcedStyle: nomixedkeys

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

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

Example: EnforcedStyle: ruby19nomixed_keys

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

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

This cop checks for places where string concatenation can be replaced with string interpolation.

The cop can autocorrect simple cases but will skip autocorrecting more complex cases where the resulting code would be harder to read. In those cases, it might be useful to extract statements to local variables or methods which you can then interpolate in a string.

NOTE: When concatenation between two strings is broken over multiple lines, this cop does not register an offense; instead, Style/LineEndConcatenation will pick up the offense if enabled.

Example:

# bad
email_with_name = user.name + ' '

# good
email_with_name = "#{user.name} "
email_with_name = format('%s ', user.name, user.email)

# accepted, line-end concatenation
name = 'First' +
  'Last'

This cop checks for places where string concatenation can be replaced with string interpolation.

The cop can autocorrect simple cases but will skip autocorrecting more complex cases where the resulting code would be harder to read. In those cases, it might be useful to extract statements to local variables or methods which you can then interpolate in a string.

NOTE: When concatenation between two strings is broken over multiple lines, this cop does not register an offense; instead, Style/LineEndConcatenation will pick up the offense if enabled.

Example:

# bad
email_with_name = user.name + ' '

# good
email_with_name = "#{user.name} "
email_with_name = format('%s ', user.name, user.email)

# accepted, line-end concatenation
name = 'First' +
  'Last'

This cop checks for places where string concatenation can be replaced with string interpolation.

The cop can autocorrect simple cases but will skip autocorrecting more complex cases where the resulting code would be harder to read. In those cases, it might be useful to extract statements to local variables or methods which you can then interpolate in a string.

NOTE: When concatenation between two strings is broken over multiple lines, this cop does not register an offense; instead, Style/LineEndConcatenation will pick up the offense if enabled.

Example:

# bad
email_with_name = user.name + ' '

# good
email_with_name = "#{user.name} "
email_with_name = format('%s ', user.name, user.email)

# accepted, line-end concatenation
name = 'First' +
  'Last'

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

Example:

# bad
1000000
1_00_000
1_0000

# good
1_000_000
1000

Example: Strict: false (default)

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

Example: Strict: true

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

This cop checks for places where string concatenation can be replaced with string interpolation.

The cop can autocorrect simple cases but will skip autocorrecting more complex cases where the resulting code would be harder to read. In those cases, it might be useful to extract statements to local variables or methods which you can then interpolate in a string.

NOTE: When concatenation between two strings is broken over multiple lines, this cop does not register an offense; instead, Style/LineEndConcatenation will pick up the offense if enabled.

Example:

# bad
email_with_name = user.name + ' '

# good
email_with_name = "#{user.name} "
email_with_name = format('%s ', user.name, user.email)

# accepted, line-end concatenation
name = 'First' +
  'Last'

This cop checks for places where string concatenation can be replaced with string interpolation.

The cop can autocorrect simple cases but will skip autocorrecting more complex cases where the resulting code would be harder to read. In those cases, it might be useful to extract statements to local variables or methods which you can then interpolate in a string.

NOTE: When concatenation between two strings is broken over multiple lines, this cop does not register an offense; instead, Style/LineEndConcatenation will pick up the offense if enabled.

Example:

# bad
email_with_name = user.name + ' '

# good
email_with_name = "#{user.name} "
email_with_name = format('%s ', user.name, user.email)

# accepted, line-end concatenation
name = 'First' +
  'Last'

Sometimes using dig method ends up with just a single argument. In such cases, dig should be replaced with [].

Example:

# bad
{ key: 'value' }.dig(:key)
[1, 2, 3].dig(0)

# good
{ key: 'value' }[:key]
[1, 2, 3][0]

# good
{ key1: { key2: 'value' } }.dig(:key1, :key2)
[1, [2, [3]]].dig(1, 1)

# good
keys = %i[key1 key2]
{ key1: { key2: 'value' } }.dig(*keys)

This cop checks whether comments have a leading space after the # denoting the start of the comment. The leading space is not required for some RDoc special syntax, like #++, #--, #:nodoc, =begin- and =end comments, "shebang" directives, or rackup options.

Example:

# bad
#Some comment

# good
# Some comment

Example: AllowDoxygenCommentStyle: false (default)

# bad

#**
# Some comment
# Another line of comment
#*

Example: AllowDoxygenCommentStyle: true

# good

#**
# Some comment
# Another line of comment
#*

Example: AllowGemfileRubyComment: false (default)

# bad

#ruby=2.7.0
#ruby-gemset=myproject

Example: AllowGemfileRubyComment: true

# good

#ruby=2.7.0
#ruby-gemset=myproject

This cop checks for send, public_send, and __send__ methods when using mix-in.

include and prepend methods were private methods until Ruby 2.0, they were mixed-in via send method. This cop uses Ruby 2.1 or higher style that can be called by public methods. And extend method that was originally a public method is also targeted for style unification.

Example:

# bad
Foo.send(:include, Bar)
Foo.send(:prepend, Bar)
Foo.send(:extend, Bar)

# bad
Foo.public_send(:include, Bar)
Foo.public_send(:prepend, Bar)
Foo.public_send(:extend, Bar)

# bad
Foo.__send__(:include, Bar)
Foo.__send__(:prepend, Bar)
Foo.__send__(:extend, Bar)

# good
Foo.include Bar
Foo.prepend Bar
Foo.extend Bar