Too Many Instance Variables is a special case of LargeClass.

Example

Given this configuration

TooManyInstanceVariables:
  max_instance_variables: 3

and this code:

class TooManyInstanceVariables
  def initialize
    @arg_1 = :dummy
    @arg_2 = :dummy
    @arg_3 = :dummy
    @arg_4 = :dummy
  end
end

Reek would emit the following warning:

test.rb -- 5 warnings:
  [1]:TooManyInstanceVariables has at least 4 instance variables (TooManyInstanceVariables)

Too Many Methods is a special case of LargeClass.

Example

Given this configuration

TooManyMethods:
  max_methods: 3

and this code:

class TooManyMethods
  def one; end
  def two; end
  def three; end
  def four; end
end

Reek would emit the following warning:

test.rb -- 1 warning:
  [1]:TooManyMethods has at least 4 methods (TooManyMethods)

A Nested Iterator occurs when a block contains another block.

Example

Given

class Duck
  class << self
    def duck_names
      %i!tick trick track!.each do |surname|
        %i!duck!.each do |last_name|
          puts "full name is #{surname} #{last_name}"
        end
      end
    end
  end
end

Reek would report the following warning:

test.rb -- 1 warning:
  [5]:Duck#duck_names contains iterators nested 2 deep (NestedIterators)

Duplication occurs when two fragments of code look nearly identical, or when two fragments of code have nearly identical effects at some conceptual level.

Reek implements a check for Duplicate Method Call.

Example

Here's a very much simplified and contrived example. The following method will report a warning:

def double_thing()
  @other.thing + @other.thing
end

One quick approach to silence Reek would be to refactor the code thus:

def double_thing()
  thing = @other.thing
  thing + thing
end

A slightly different approach would be to replace all calls of double_thing by calls to @other.double_thing:

class Other
  def double_thing()
    thing + thing
  end
end

The approach you take will depend on balancing other factors in your code.

Duplication occurs when two fragments of code look nearly identical, or when two fragments of code have nearly identical effects at some conceptual level.

Reek implements a check for Duplicate Method Call.

Example

Here's a very much simplified and contrived example. The following method will report a warning:

def double_thing()
  @other.thing + @other.thing
end

One quick approach to silence Reek would be to refactor the code thus:

def double_thing()
  thing = @other.thing
  thing + thing
end

A slightly different approach would be to replace all calls of double_thing by calls to @other.double_thing:

class Other
  def double_thing()
    thing + thing
  end
end

The approach you take will depend on balancing other factors in your code.

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

A candidate method for the Missing Safe Method smell are methods whose names end with an exclamation mark.

An exclamation mark in method names means (the explanation below is taken from here ):

The ! in method names that end with ! means, “This method is dangerous”—or, more precisely, this method is the “dangerous” version of an otherwise equivalent method, with the same name minus the !. “Danger” is relative; the ! doesn’t mean anything at all unless the method name it’s in corresponds to a similar but bang-less method name. So, for example, gsub! is the dangerous version of gsub. exit! is the dangerous version of exit. flatten! is the dangerous version of flatten. And so forth.

Such a method is called Missing Safe Method if and only if her non-bang version does not exist and this method is reported as a smell.

Example

Given

class C
  def foo; end
  def foo!; end
  def bar!; end
end

Reek would report bar! as Missing Safe Method smell but not foo!.

Reek reports this smell only in a class context, not in a module context in order to allow perfectly legit code like this:

class Parent
  def foo; end
end

module Dangerous
  def foo!; end
end

class Son < Parent
  include Dangerous
end

class Daughter < Parent
end

In this example, Reek would not report the Missing Safe Method smell for the method foo of the Dangerous module.

A candidate method for the Missing Safe Method smell are methods whose names end with an exclamation mark.

An exclamation mark in method names means (the explanation below is taken from here ):

The ! in method names that end with ! means, “This method is dangerous”—or, more precisely, this method is the “dangerous” version of an otherwise equivalent method, with the same name minus the !. “Danger” is relative; the ! doesn’t mean anything at all unless the method name it’s in corresponds to a similar but bang-less method name. So, for example, gsub! is the dangerous version of gsub. exit! is the dangerous version of exit. flatten! is the dangerous version of flatten. And so forth.

Such a method is called Missing Safe Method if and only if her non-bang version does not exist and this method is reported as a smell.

Example

Given

class C
  def foo; end
  def foo!; end
  def bar!; end
end

Reek would report bar! as Missing Safe Method smell but not foo!.

Reek reports this smell only in a class context, not in a module context in order to allow perfectly legit code like this:

class Parent
  def foo; end
end

module Dangerous
  def foo!; end
end

class Son < Parent
  include Dangerous
end

class Daughter < Parent
end

In this example, Reek would not report the Missing Safe Method smell for the method foo of the Dangerous module.

A candidate method for the Missing Safe Method smell are methods whose names end with an exclamation mark.

An exclamation mark in method names means (the explanation below is taken from here ):

The ! in method names that end with ! means, “This method is dangerous”—or, more precisely, this method is the “dangerous” version of an otherwise equivalent method, with the same name minus the !. “Danger” is relative; the ! doesn’t mean anything at all unless the method name it’s in corresponds to a similar but bang-less method name. So, for example, gsub! is the dangerous version of gsub. exit! is the dangerous version of exit. flatten! is the dangerous version of flatten. And so forth.

Such a method is called Missing Safe Method if and only if her non-bang version does not exist and this method is reported as a smell.

Example

Given

class C
  def foo; end
  def foo!; end
  def bar!; end
end

Reek would report bar! as Missing Safe Method smell but not foo!.

Reek reports this smell only in a class context, not in a module context in order to allow perfectly legit code like this:

class Parent
  def foo; end
end

module Dangerous
  def foo!; end
end

class Son < Parent
  include Dangerous
end

class Daughter < Parent
end

In this example, Reek would not report the Missing Safe Method smell for the method foo of the Dangerous module.