Metrics

Metrics/AbcSize

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.27

1.5

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 and https://en.wikipedia.org/wiki/ABC_Software_Metric.

Interpreting ABC size:

  • ⇐ 17 satisfactory

  • 18..30 unsatisfactory

  • > 30 dangerous

You can have repeated "attributes" calls count as a single "branch". For this purpose, attributes are any method with no argument; no attempt is meant to distinguish actual attr_reader from other methods.

This cop also takes into account AllowedMethods (defaults to []) And AllowedPatterns (defaults to [])

Examples

CountRepeatedAttributes: false (default is true)

# `model` and `current_user`, referenced 3 times each,
# are each counted as only 1 branch each if
# `CountRepeatedAttributes` is set to 'false'

def search
  @posts = model.active.visible_by(current_user)
            .search(params[:q])
  @posts = model.some_process(@posts, current_user)
  @posts = model.another_process(@posts, current_user)

  render 'pages/search/page'
end

Configurable attributes

Name Default value Configurable values

AllowedMethods

[]

Array

AllowedPatterns

[]

Array

CountRepeatedAttributes

true

Boolean

Max

17

Integer

References

Metrics/BlockLength

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.44

1.5

Checks if the length of a block exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable. The cop can be configured to ignore blocks passed to certain methods.

You can set constructs you want to fold with CountAsOne. Available are: 'array', 'hash', 'heredoc', and 'method_call'. Each construct will be counted as one line regardless of its actual size.

This cop does not apply for Struct definitions.
The ExcludedMethods configuration is deprecated and only kept for backwards compatibility. Please use AllowedMethods and AllowedPatterns instead. By default, there are no methods to allowed.

Examples

CountAsOne: ['array', 'heredoc', 'method_call']

something do
  array = [         # +1
    1,
    2
  ]

  hash = {          # +3
    key: 'value'
  }

  msg = <<~HEREDOC  # +1
    Heredoc
    content.
  HEREDOC

  foo(              # +1
    1,
    2
  )
end                 # 6 points

Configurable attributes

Name Default value Configurable values

CountComments

false

Boolean

Max

25

Integer

CountAsOne

[]

Array

AllowedMethods

refine

Array

AllowedPatterns

[]

Array

Exclude

**/*.gemspec

Array

Metrics/BlockNesting

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.25

1.65

Checks for excessive nesting of conditional and looping constructs.

You can configure if blocks are considered using the CountBlocks and CountModifierForms options. When both are set to false (the default) blocks and modifier forms are not counted towards the nesting level. Set them to true to include these in the nesting level calculation as well.

The maximum level of nesting allowed is configurable.

Configurable attributes

Name Default value Configurable values

CountBlocks

false

Boolean

CountModifierForms

false

Boolean

Max

3

Integer

References

Metrics/ClassLength

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.25

0.87

Checks if the length of a class exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

You can set constructs you want to fold with CountAsOne. Available are: 'array', 'hash', 'heredoc', and 'method_call'. Each construct will be counted as one line regardless of its actual size.

This cop also applies for Struct definitions.

Examples

CountAsOne: ['array', 'heredoc', 'method_call']

class Foo
  ARRAY = [         # +1
    1,
    2
  ]

  HASH = {          # +3
    key: 'value'
  }

  MSG = <<~HEREDOC  # +1
    Heredoc
    content.
  HEREDOC

  foo(              # +1
    1,
    2
  )
end                 # 6 points

Configurable attributes

Name Default value Configurable values

CountComments

false

Boolean

Max

100

Integer

CountAsOne

[]

Array

Metrics/CollectionLiteralLength

Enabled by default Safe Supports autocorrection Version Added Version Changed

Pending

Yes

No

1.47

-

Checks for literals with extremely many entries. This is indicative of configuration or data that may be better extracted somewhere else, like a database, fetched from an API, or read from a non-code file (CSV, JSON, YAML, etc.).

Examples

# bad
# Huge Array literal
[1, 2, '...', 999_999_999]

# bad
# Huge Hash literal
{ 1 => 1, 2 => 2, '...' => '...', 999_999_999 => 999_999_999}

# bad
# Huge Set "literal"
Set[1, 2, '...', 999_999_999]

# good
# Reasonably sized Array literal
[1, 2, '...', 10]

# good
# Reading huge Array from external data source
# File.readlines('numbers.txt', chomp: true).map!(&:to_i)

# good
# Reasonably sized Hash literal
{ 1 => 1, 2 => 2, '...' => '...', 10 => 10}

# good
# Reading huge Hash from external data source
CSV.foreach('numbers.csv', headers: true).each_with_object({}) do |row, hash|
  hash[row["key"].to_i] = row["value"].to_i
end

# good
# Reasonably sized Set "literal"
Set[1, 2, '...', 10]

# good
# Reading huge Set from external data source
SomeFramework.config_for(:something)[:numbers].to_set

Configurable attributes

Name Default value Configurable values

LengthThreshold

250

Integer

Metrics/CyclomaticComplexity

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.25

0.81

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. Blocks that are calls to builtin iteration methods (e.g. `ary.map{…​}) also add one, others are ignored.

def each_child_node(*types)               # count begins: 1
  unless block_given?                     # unless: +1
    return to_enum(__method__, *types)
children.each do |child|                # each{}: +1
  next unless child.is_a?(Node)         # unless: +1
  yield child if types.empty? ||        # if: +1, ||: +1
                 types.include?(child.type)
end
  self
end                                       # total: 6

Configurable attributes

Name Default value Configurable values

AllowedMethods

[]

Array

AllowedPatterns

[]

Array

Max

7

Integer

Metrics/MethodLength

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.25

1.5

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

You can set constructs you want to fold with CountAsOne. Available are: 'array', 'hash', 'heredoc', and 'method_call'. Each construct will be counted as one line regardless of its actual size.

The ExcludedMethods and IgnoredMethods configuration is deprecated and only kept for backwards compatibility. Please use AllowedMethods and AllowedPatterns instead. By default, there are no methods to allowed.

Examples

CountAsOne: ['array', 'heredoc', 'method_call']

def m
  array = [       # +1
    1,
    2
  ]

  hash = {        # +3
    key: 'value'
  }

  <<~HEREDOC      # +1
    Heredoc
    content.
  HEREDOC

  foo(            # +1
    1,
    2
  )
end               # 6 points

Configurable attributes

Name Default value Configurable values

CountComments

false

Boolean

Max

10

Integer

CountAsOne

[]

Array

AllowedMethods

[]

Array

AllowedPatterns

[]

Array

References

Metrics/ModuleLength

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.31

0.87

Checks if the length of a module exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

You can set constructs you want to fold with CountAsOne. Available are: 'array', 'hash', 'heredoc', and 'method_call'. Each construct will be counted as one line regardless of its actual size.

Examples

CountAsOne: ['array', 'heredoc', 'method_call']

module M
  ARRAY = [         # +1
    1,
    2
  ]

  HASH = {          # +3
    key: 'value'
  }

  MSG = <<~HEREDOC  # +1
    Heredoc
    content.
  HEREDOC

  foo(              # +1
    1,
    2
  )
end                 # 6 points

Configurable attributes

Name Default value Configurable values

CountComments

false

Boolean

Max

100

Integer

CountAsOne

[]

Array

Metrics/ParameterLists

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.25

1.5

Checks for methods with too many parameters.

The maximum number of parameters is configurable. Keyword arguments can optionally be excluded from the total count, as they add less complexity than positional or optional parameters.

Any number of arguments for initialize method inside a block of Struct.new and Data.define like this is always allowed:

Struct.new(:one, :two, :three, :four, :five, keyword_init: true) do
  def initialize(one:, two:, three:, four:, five:)
  end
end

This is because checking the number of arguments of the initialize method does not make sense.

Explicit block argument &block is not counted to prevent erroneous change that is avoided by making block argument implicit.

This cop also checks for the maximum number of optional parameters. This can be configured using the MaxOptionalParameters config option.

Examples

Max: 3

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

Max: 2

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

CountKeywordArgs: true (default)

# counts keyword args towards the maximum

# bad (assuming Max is 3)
def foo(a, b, c, d: 1)
end

# good (assuming Max is 3)
def foo(a, b, c: 1)
end

CountKeywordArgs: false

# don't count keyword args towards the maximum

# good (assuming Max is 3)
def foo(a, b, c, d: 1)
end

MaxOptionalParameters: 3 (default)

# good
def foo(a = 1, b = 2, c = 3)
end

MaxOptionalParameters: 2

# bad
def foo(a = 1, b = 2, c = 3)
end

Configurable attributes

Name Default value Configurable values

Max

5

Integer

CountKeywordArgs

true

Boolean

MaxOptionalParameters

3

Integer

References

Metrics/PerceivedComplexity

Enabled by default Safe Supports autocorrection Version Added Version Changed

Enabled

Yes

No

0.25

0.81

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.

Examples

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

Configurable attributes

Name Default value Configurable values

AllowedMethods

[]

Array

AllowedPatterns

[]

Array

Max

8

Integer