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 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.

This cop checks the length of lines in the source code. The maximum length is configurable. The tab size is configured in the IndentationWidth of the Layout/IndentationStyle cop. It also ignores a shebang line by default.

This cop has some autocorrection capabilities. It can programmatically shorten certain long lines by inserting line breaks into expressions that can be safely split across lines. These include arrays, hashes, and method calls with argument lists.

If autocorrection is enabled, the following Layout cops are recommended to further format the broken lines. (Many of these are enabled by default.)

- ArgumentAlignment
- BlockAlignment
- BlockDelimiters
- BlockEndNewline
- ClosingParenthesisIndentation
- FirstArgumentIndentation
- FirstArrayElementIndentation
- FirstHashElementIndentation
- FirstParameterIndentation
- HashAlignment
- IndentationWidth
- MultilineArrayLineBreaks
- MultilineBlockLayout
- MultilineHashBraceLayout
- MultilineHashKeyLineBreaks
- MultilineMethodArgumentLineBreaks
- ParameterAlignment

Together, these cops will pretty print hashes, arrays, method calls, etc. For example, let's say the max columns is 25:

Example:

# bad
{foo: "0000000000", bar: "0000000000", baz: "0000000000"}

# good
{foo: "0000000000",
bar: "0000000000", baz: "0000000000"}

# good (with recommended cops enabled)
{
  foo: "0000000000",
  bar: "0000000000",
  baz: "0000000000",
}

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop 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

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop 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

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, constant definitions or constant visibility declarations.

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

module Math
end

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

# allowed
  # Class without body
  class Person
  end

  # Namespace - A namespace can be a class or a module
  # Containing a class
  module Namespace
    # Description/Explanation of Person class
    class Person
      # ...
    end
  end

  # Containing constant visibility declaration
  module Namespace
    class Private
    end

    private_constant :Private
  end

  # Containing constant definition
  module Namespace
    Public = Class.new
  end

This cop 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

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop 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

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop 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

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
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 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 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 that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop 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

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end

This cop checks that the indentation method is consistent. Either tabs only or spaces only are used for indentation.

Example: EnforcedStyle: spaces (default)

# bad
# This example uses a tab to indent bar.
def foo
  bar
end

# good
# This example uses spaces to indent bar.
def foo
  bar
end

Example: EnforcedStyle: tabs

# bad
# This example uses spaces to indent bar.
def foo
  bar
end

# good
# This example uses a tab to indent bar.
def foo
  bar
end