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

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 for the correct use of Date methods, such as Date.today, Date.current etc.

Using Date.today is dangerous, because it doesn't know anything about Rails time zone. You must use Time.zone.today instead.

The cop also reports warnings when you are using to_time method, because it doesn't know about Rails time zone either.

Two styles are supported for this cop. When EnforcedStyle is 'strict' then the Date methods today, current, yesterday, and tomorrow are prohibited and the usage of both to_time and 'totimeincurrentzone' are reported as warning.

When EnforcedStyle is 'flexible' then only Date.today is prohibited and only to_time is reported as warning.

Example: EnforcedStyle: strict

# bad
Date.current
Date.yesterday
Date.today
date.to_time

# good
Time.zone.today
Time.zone.today - 1.day

Example: EnforcedStyle: flexible (default)

# bad
Date.today
date.to_time

# good
Time.zone.today
Time.zone.today - 1.day
Date.current
Date.yesterday
date.in_time_zone

This cop identifies possible cases where Active Record save! or related should be used instead of save because the model might have failed to save and an exception is better than unhandled failure.

This will allow: - update or save calls, assigned to a variable, or used as a condition in an if/unless/case statement. - create calls, assigned to a variable that then has a call to persisted?. - calls if the result is explicitly returned from methods and blocks, or provided as arguments. - calls whose signature doesn't look like an ActiveRecord persistence method.

By default it will also allow implicit returns from methods and blocks. that behavior can be turned off with AllowImplicitReturn: false.

You can permit receivers that are giving false positives with AllowedReceivers: []

Example:

# bad
user.save
user.update(name: 'Joe')
user.find_or_create_by(name: 'Joe')
user.destroy

# good
unless user.save
  # ...
end
user.save!
user.update!(name: 'Joe')
user.find_or_create_by!(name: 'Joe')
user.destroy!

user = User.find_or_create_by(name: 'Joe')
unless user.persisted?
  # ...
end

def save_user
  return user.save
end

Example: AllowImplicitReturn: true (default)

# good
users.each { |u| u.save }

def save_user
  user.save
end

Example: AllowImplicitReturn: false

# bad
users.each { |u| u.save }
def save_user
  user.save
end

# good
users.each { |u| u.save! }

def save_user
  user.save!
end

def save_user
  return user.save
end

Example: AllowedReceivers: ['merchant.customers', 'Service::Mailer']

# bad
merchant.create
customers.builder.save
Mailer.create

module Service::Mailer
  self.create
end

# good
merchant.customers.create
MerchantService.merchant.customers.destroy
Service::Mailer.update(message: 'Message')
::Service::Mailer.update
Services::Service::Mailer.update(message: 'Message')
Service::Mailer::update

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 46.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76