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 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 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 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 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

This cop identifies places where a case-insensitive string comparison can better be implemented using casecmp.

Example:

# bad
str.downcase == 'abc'
str.upcase.eql? 'ABC'
'abc' == str.downcase
'ABC'.eql? str.upcase
str.downcase == str.downcase

# good
str.casecmp('ABC').zero?
'abc'.casecmp(str).zero?

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.

Example: 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)

Example: EnforcedStyle: compact

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

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

This cop checks for unused block arguments.

Example:

# bad

do_something do |used, unused|
  puts used
end

do_something do |bar|
  puts :foo
end

define_method(:foo) do |bar|
  puts :baz
end

Example:

#good

do_something do |used, _unused|
  puts used
end

do_something do
  puts :foo
end

define_method(:foo) do |_bar|
  puts :baz
end

This cop makes sure that predicates are named properly.

Example:

# bad
def is_even?(value)
end

# good
def even?(value)
end

# bad
def has_value?
end

# good
def value?
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

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

Example:

# 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

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.

Example: EnforcedStyle: format(default)

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

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

Example: EnforcedStyle: sprintf

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

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

Example: EnforcedStyle: percent

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

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

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.

Example: 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)

Example: EnforcedStyle: compact

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

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

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 Interger polymorphic.

Example: EnforcedStyle: predicate (default)

# bad

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

# good

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

Example: EnforcedStyle: comparison

# bad

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

# good

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

Use a consistent style for named format string tokens.

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

Example: EnforcedStyle: annotated (default)

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

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

Example: EnforcedStyle: template

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

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

Example: EnforcedStyle: unannotated

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

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

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

Example:

# 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

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

Example:

# bad
"#{@var}"

# good
@var.to_s

# good if @var is already a String
@var

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

Example:

# 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

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

Example:

# bad
if condition
  do_stuff(bar)
end

unless qux.empty?
  Foo.do_something
end

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

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.

Example: 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)

Example: EnforcedStyle: compact

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

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