This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop tries to produce a complexity score that's a measure of the complexity the reader experiences when looking at a method. For that reason it considers when nodes as something that doesn't add as much complexity as an if or a &&. Except if it's one of those special case/when constructs where there's no expression after case. Then the cop treats it as an if/elsif/elsif... and lets all the when nodes count. In contrast to the CyclomaticComplexity cop, this cop considers else nodes as adding complexity.

Example:

def my_method                   # 1
  if cond                       # 1
    case var                    # 2 (0.8 + 4 * 0.2, rounded)
    when 1 then func_one
    when 2 then func_two
    when 3 then func_three
    when 4..10 then func_other
    end
  else                          # 1
    do_something until a && b   # 2
  end                           # ===
end                             # 7 complexity points

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Checks if uses of quotes match the configured preference.

Example: 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}!"

Example: 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"

This cop checks whether method definitions are separated by one empty line.

NumberOfEmptyLines can be and integer (e.g. 1 by default) or an array (e.g. [1, 2]) to specificy a minimum and a maximum of empty lines.

AllowAdjacentOneLineDefs can be used to configure is adjacent one line methods definitions are an offense

Example:

# bad
def a
end
def b
end

Example:

# good
def a
end

def b
end

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

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

Example:

# bad
class Person
  # ...
end

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

This cop checks for rescue blocks with no body.

Example:

# bad

def some_method
  do_something
rescue
  # do nothing
end

Example:

# bad

begin
  do_something
rescue
  # do nothing
end

Example:

# good

def some_method
  do_something
rescue
  handle_exception
end

Example:

# good

begin
  do_something
rescue
  handle_exception
end

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.

Example: EnforcedStyle: always (default)

# bad
foo.save and return

# bad
if foo and bar
end

# good
foo.save && return

# good
if foo && bar
end

Example: EnforcedStyle: conditionals

# bad
if foo and bar
end

# good
foo.save && return

# good
foo.save and return

# good
if foo && bar
end

This cop checks whether method definitions are separated by one empty line.

NumberOfEmptyLines can be and integer (e.g. 1 by default) or an array (e.g. [1, 2]) to specificy a minimum and a maximum of empty lines.

AllowAdjacentOneLineDefs can be used to configure is adjacent one line methods definitions are an offense

Example:

# bad
def a
end
def b
end

Example:

# good
def a
end

def b
end

This cops checks for two or more consecutive blank lines.

Example:

# bad - It has two empty lines.
some_method
# one empty line
# two empty lines
some_method

# good
some_method
# one empty line
some_method

This cops checks for two or more consecutive blank lines.

Example:

# bad - It has two empty lines.
some_method
# one empty line
# two empty lines
some_method

# good
some_method
# one empty line
some_method

This cops checks for two or more consecutive blank lines.

Example:

# bad - It has two empty lines.
some_method
# one empty line
# two empty lines
some_method

# good
some_method
# one empty line
some_method

Modifiers should be indented as deep as method definitions, or as deep as the class/module keyword, depending on configuration.

Example: EnforcedStyle: indent (default)

# bad
class Plumbus
private
  def smooth; end
end

# good
class Plumbus
  private
  def smooth; end
end

Example: EnforcedStyle: outdent

# bad
class Plumbus
  private
  def smooth; end
end

# good
class Plumbus
private
  def smooth; end
end

This cops checks for two or more consecutive blank lines.

Example:

# bad - It has two empty lines.
some_method
# one empty line
# two empty lines
some_method

# good
some_method
# one empty line
some_method

Checks that the equals signs in parameter default assignments have or don't have surrounding space depending on configuration.

Example:

# bad
def some_method(arg1=:default, arg2=nil, arg3=[])
  # do something...
end

# good
def some_method(arg1 = :default, arg2 = nil, arg3 = [])
  # do something...
end

Checks if uses of quotes match the configured preference.

Example: 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}!"

Example: 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"

This cops checks for two or more consecutive blank lines.

Example:

# bad - It has two empty lines.
some_method
# one empty line
# two empty lines
some_method

# good
some_method
# one empty line
some_method

This cop checks for ambiguous operators in the first argument of a method invocation without parentheses.

Example:

# bad

# The `*` is interpreted as a splat operator but it could possibly be
# a `*` method invocation (i.e. `do_something.*(some_array)`).
do_something *some_array

Example:

# good

# With parentheses, there's no ambiguity.
do_something(*some_array)

This cops checks if empty lines around the bodies of classes match the configuration.

Example: EnforcedStyle: empty_lines

# good

class Foo

  def bar
    # ...
  end

end

Example: EnforcedStyle: emptylinesexcept_namespace

# good

class Foo
  class Bar

    # ...

  end
end

Example: EnforcedStyle: emptylinesspecial

# good
class Foo

  def bar; end

end

Example: EnforcedStyle: noemptylines (default)

# good

class Foo
  def bar
    # ...
  end
end

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.

Example:

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

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

# bad
%W(alpha #{beta})

# bad
%I(alpha beta)

This cops checks for two or more consecutive blank lines.

Example:

# bad - It has two empty lines.
some_method
# one empty line
# two empty lines
some_method

# good
some_method
# one empty line
some_method