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 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

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 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.

This cop checks for every useless assignment to local variable in every scope. The basic idea for this cop was from the warning of ruby -cw:

assigned but unused variable - foo

Currently this cop has advanced logic that detects unreferenced reassignments and properly handles varied cases such as branch, loop, rescue, ensure, etc.

Example:

# bad

def some_method
  some_var = 1
  do_something
end

Example:

# good

def some_method
  some_var = 1
  do_something(some_var)
end

This cop checks the indentation of the first parameter in a method call. Parameters after the first one are checked by Style/AlignParameters, not by this cop.

Example:

# bad
some_method(
first_param,
second_param)

# good
some_method(
  first_param,
second_param)

This cop checks the indentation of the first element in an array literal where the opening bracket and the first element are on separate lines. The other elements' indentations are handled by the AlignArray cop.

By default, array literals that are arguments in a method call with parentheses, and where the opening square bracket of the array is on the same line as the opening parenthesis of the method call, shall have their first element indented one step (two spaces) more than the position inside the opening parenthesis.

Other array literals shall have their first element indented one step more than the start of the line where the opening square bracket is.

This default style is called 'specialinsideparentheses'. Alternative styles are 'consistent' and 'align_brackets'. Here are examples:

Example: EnforcedStyle: specialinsideparentheses (default)

# The `special_inside_parentheses` style enforces that the first
# element in an array literal where the opening bracket and first
# element are on seprate lines is indented one step (two spaces) more
# than the position inside the opening parenthesis.

#bad
array = [
  :value
]
and_in_a_method_call([
  :no_difference
                     ])

#good
array = [
  :value
]
but_in_a_method_call([
                       :its_like_this
                     ])

Example: EnforcedStyle: consistent

# The `consistent` style enforces that the first element in an array
# literal where the opening bracket and the first element are on
# seprate lines is indented the same as an array literal which is not
# defined inside a method call.

#bad
# consistent
array = [
  :value
]
but_in_a_method_call([
                       :its_like_this
])

#good
array = [
  :value
]
and_in_a_method_call([
  :no_difference
])

Example: EnforcedStyle: align_brackets

# The `align_brackets` style enforces that the opening and closing
# brackets are indented to the same position.

#bad
# align_brackets
and_now_for_something = [
                          :completely_different
]

#good
# align_brackets
and_now_for_something = [
                          :completely_different
                        ]

This cops checks if empty lines exist around the bodies of methods.

Example:

# good

def foo
  # ...
end

# bad

def bar

  # ...

end

Checks for comma (,) not followed by some kind of space.

Example:

# bad
[1,2]
{ foo:bar,}

# good
[1, 2]
{ foo:bar, }

Checks that operators have space around them, except for ** which should not have surrounding space.

Example:

# bad
total = 3*4
"apple"+"juice"
my_number = 38/4
a ** b

# good
total = 3 * 4
"apple" + "juice"
my_number = 38 / 4
a**b

Checks for comma (,) not followed by some kind of space.

Example:

# bad
[1,2]
{ foo:bar,}

# good
[1, 2]
{ foo:bar, }

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.

This cop checks for extra/unnecessary whitespace.

Example:

# good if AllowForAlignment is true
name      = "RuboCop"
# Some comment and an empty line

website  += "/bbatsov/rubocop" unless cond
puts        "rubocop"          if     debug

# bad for any configuration
set_app("RuboCop")
website  = "https://github.com/bbatsov/rubocop"

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