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.

Too Many Constants is a special case of LargeClass.

Example

Given this configuration

TooManyConstants:
  max_constants: 3

and this code:

class TooManyConstants
  CONST_1 = :dummy
  CONST_2 = :dummy
  CONST_3 = :dummy
  CONST_4 = :dummy
end

Reek would emit the following warning:

test.rb -- 1 warnings:
  [1]:TooManyConstants has 4 constants (TooManyConstants)

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 NilCheck is a type check. Failures of NilCheck violate the "tell, don't ask" principle.

Additionally, type checks often mask bigger problems in your source code like not using OOP and / or polymorphism when you should.

Example

Given

class Klass
  def nil_checker(argument)
    if argument.nil?
      puts "argument isn't nil!"
    end
  end
end

Reek would emit the following warning:

test.rb -- 1 warning:
  [3]:Klass#nil_checker performs a nil-check. (NilCheck)

This cop checks whether some constant value isn't a mutable literal (e.g. array or hash).

Example:

# bad
CONST = [1, 2, 3]

# good
CONST = [1, 2, 3].freeze