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 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

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.

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 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.

Example: EnforcedStyle: percent (default)

# good
%w[foo bar baz]

# bad
['foo', 'bar', 'baz']

Example: EnforcedStyle: brackets

# good
['foo', 'bar', 'baz']

# bad
%w[foo bar baz]

Checks that block braces have or don't have surrounding space inside them on configuration. For blocks taking parameters, it checks that the left brace has or doesn't have trailing space depending on configuration.

Example: EnforcedStyle: space (default)

# The `space` style enforces that block braces have
# surrounding space.

# bad
some_array.each {puts e}

# good
some_array.each { puts e }

Example: EnforcedStyle: no_space

# The `no_space` style enforces that block braces don't
# have surrounding space.

# bad
some_array.each { puts e }

# good
some_array.each {puts e}

Example: EnforcedStyleForEmptyBraces: no_space (default)

# The `no_space` EnforcedStyleForEmptyBraces style enforces that
# block braces don't have a space in between when empty.

# bad
some_array.each {   }
some_array.each {  }
some_array.each { }

# good
some_array.each {}

Example: EnforcedStyleForEmptyBraces: space

# The `space` EnforcedStyleForEmptyBraces style enforces that
# block braces have at least a spece in between when empty.

# bad
some_array.each {}

# good
some_array.each { }
some_array.each {  }
some_array.each {   }

Example: SpaceBeforeBlockParameters: true (default)

# The SpaceBeforeBlockParameters style set to `true` enforces that
# there is a space between `{` and `|`. Overrides `EnforcedStyle`
# if there is a conflict.

# bad
[1, 2, 3].each {|n| n * 2 }

# good
[1, 2, 3].each { |n| n * 2 }

Example: SpaceBeforeBlockParameters: true

# The SpaceBeforeBlockParameters style set to `false` enforces that
# there is no space between `{` and `|`. Overrides `EnforcedStyle`
# if there is a conflict.

# bad
[1, 2, 3].each { |n| n * 2 }

# good
[1, 2, 3].each {|n| n * 2 }

Checks that block braces have or don't have surrounding space inside them on configuration. For blocks taking parameters, it checks that the left brace has or doesn't have trailing space depending on configuration.

Example: EnforcedStyle: space (default)

# The `space` style enforces that block braces have
# surrounding space.

# bad
some_array.each {puts e}

# good
some_array.each { puts e }

Example: EnforcedStyle: no_space

# The `no_space` style enforces that block braces don't
# have surrounding space.

# bad
some_array.each { puts e }

# good
some_array.each {puts e}

Example: EnforcedStyleForEmptyBraces: no_space (default)

# The `no_space` EnforcedStyleForEmptyBraces style enforces that
# block braces don't have a space in between when empty.

# bad
some_array.each {   }
some_array.each {  }
some_array.each { }

# good
some_array.each {}

Example: EnforcedStyleForEmptyBraces: space

# The `space` EnforcedStyleForEmptyBraces style enforces that
# block braces have at least a spece in between when empty.

# bad
some_array.each {}

# good
some_array.each { }
some_array.each {  }
some_array.each {   }

Example: SpaceBeforeBlockParameters: true (default)

# The SpaceBeforeBlockParameters style set to `true` enforces that
# there is a space between `{` and `|`. Overrides `EnforcedStyle`
# if there is a conflict.

# bad
[1, 2, 3].each {|n| n * 2 }

# good
[1, 2, 3].each { |n| n * 2 }

Example: SpaceBeforeBlockParameters: true

# The SpaceBeforeBlockParameters style set to `false` enforces that
# there is no space between `{` and `|`. Overrides `EnforcedStyle`
# if there is a conflict.

# bad
[1, 2, 3].each { |n| n * 2 }

# good
[1, 2, 3].each {|n| n * 2 }

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

Example: EnforcedStyle: empty_lines

# good

module Foo

  def bar
    # ...
  end

end

Example: EnforcedStyle: emptylinesexcept_namespace

# good

module Foo
  module Bar

    # ...

  end
end

Example: EnforcedStyle: emptylinesspecial

# good
module Foo

  def bar; end

end

Example: EnforcedStyle: noemptylines (default)

# good

module Foo
  def bar
    # ...
  end
end

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

Example: EnforcedStyle: empty_lines

# good

module Foo

  def bar
    # ...
  end

end

Example: EnforcedStyle: emptylinesexcept_namespace

# good

module Foo
  module Bar

    # ...

  end
end

Example: EnforcedStyle: emptylinesspecial

# good
module Foo

  def bar; end

end

Example: EnforcedStyle: noemptylines (default)

# good

module Foo
  def bar
    # ...
  end
end

This cop checks the style of children definitions at classes and modules. Basically there are two different styles:

Example: EnforcedStyle: nested (default)

# good
# have each child on its own line
class Foo
  class Bar
  end
end

Example: EnforcedStyle: compact

# good
# combine definitions as much as possible
class Foo::Bar
end

The compact style is only forced for classes/modules with one child.

Checks that block braces have or don't have a space before the opening brace depending on configuration.

Example:

# bad
foo.map{ |a|
  a.bar.to_s
}

# good
foo.map { |a|
  a.bar.to_s
}

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 cops checks for indentation that doesn't use the specified number of spaces.

See also the IndentationConsistency cop which is the companion to this one.

Example:

# bad
class A
 def test
  puts 'hello'
 end
end

# good
class A
  def test
    puts 'hello'
  end
end

Example: IgnoredPatterns: ['^\s*module']

# bad
module A
class B
  def test
  puts 'hello'
  end
end
end

# good
module A
class B
  def test
    puts 'hello'
  end
end
end

Checks that block braces have or don't have surrounding space inside them on configuration. For blocks taking parameters, it checks that the left brace has or doesn't have trailing space depending on configuration.

Example: EnforcedStyle: space (default)

# The `space` style enforces that block braces have
# surrounding space.

# bad
some_array.each {puts e}

# good
some_array.each { puts e }

Example: EnforcedStyle: no_space

# The `no_space` style enforces that block braces don't
# have surrounding space.

# bad
some_array.each { puts e }

# good
some_array.each {puts e}

Example: EnforcedStyleForEmptyBraces: no_space (default)

# The `no_space` EnforcedStyleForEmptyBraces style enforces that
# block braces don't have a space in between when empty.

# bad
some_array.each {   }
some_array.each {  }
some_array.each { }

# good
some_array.each {}

Example: EnforcedStyleForEmptyBraces: space

# The `space` EnforcedStyleForEmptyBraces style enforces that
# block braces have at least a spece in between when empty.

# bad
some_array.each {}

# good
some_array.each { }
some_array.each {  }
some_array.each {   }

Example: SpaceBeforeBlockParameters: true (default)

# The SpaceBeforeBlockParameters style set to `true` enforces that
# there is a space between `{` and `|`. Overrides `EnforcedStyle`
# if there is a conflict.

# bad
[1, 2, 3].each {|n| n * 2 }

# good
[1, 2, 3].each { |n| n * 2 }

Example: SpaceBeforeBlockParameters: true

# The SpaceBeforeBlockParameters style set to `false` enforces that
# there is no space between `{` and `|`. Overrides `EnforcedStyle`
# if there is a conflict.

# bad
[1, 2, 3].each { |n| n * 2 }

# good
[1, 2, 3].each {|n| n * 2 }

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

Example:

# good
method1(method2(arg), method3(arg))

# bad
method1(method2 arg, method3, arg)

Checks that block braces have or don't have a space before the opening brace depending on configuration.

Example:

# bad
foo.map{ |a|
  a.bar.to_s
}

# good
foo.map { |a|
  a.bar.to_s
}

Checks that block braces have or don't have surrounding space inside them on configuration. For blocks taking parameters, it checks that the left brace has or doesn't have trailing space depending on configuration.

Example: EnforcedStyle: space (default)

# The `space` style enforces that block braces have
# surrounding space.

# bad
some_array.each {puts e}

# good
some_array.each { puts e }

Example: EnforcedStyle: no_space

# The `no_space` style enforces that block braces don't
# have surrounding space.

# bad
some_array.each { puts e }

# good
some_array.each {puts e}

Example: EnforcedStyleForEmptyBraces: no_space (default)

# The `no_space` EnforcedStyleForEmptyBraces style enforces that
# block braces don't have a space in between when empty.

# bad
some_array.each {   }
some_array.each {  }
some_array.each { }

# good
some_array.each {}

Example: EnforcedStyleForEmptyBraces: space

# The `space` EnforcedStyleForEmptyBraces style enforces that
# block braces have at least a spece in between when empty.

# bad
some_array.each {}

# good
some_array.each { }
some_array.each {  }
some_array.each {   }

Example: SpaceBeforeBlockParameters: true (default)

# The SpaceBeforeBlockParameters style set to `true` enforces that
# there is a space between `{` and `|`. Overrides `EnforcedStyle`
# if there is a conflict.

# bad
[1, 2, 3].each {|n| n * 2 }

# good
[1, 2, 3].each { |n| n * 2 }

Example: SpaceBeforeBlockParameters: true

# The SpaceBeforeBlockParameters style set to `false` enforces that
# there is no space between `{` and `|`. Overrides `EnforcedStyle`
# if there is a conflict.

# bad
[1, 2, 3].each { |n| n * 2 }

# good
[1, 2, 3].each {|n| n * 2 }

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

Example:

# good
method1(method2(arg), method3(arg))

# bad
method1(method2 arg, method3, arg)

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

Example:

# good
method1(method2(arg), method3(arg))

# bad
method1(method2 arg, method3, arg)