I'm really proud to announce my new contribuition to RuboCop.

Some days ago I contributed improving the development page, creating a getting started guide and also creating a new tutorial to explain how Node Pattern works.

Now, the Layout/ClassStructure cop was merged and it allows us to specify the order of the elements in the class definition.

Initially it follows the community style guide and follows the order:

  1. Include, Extend or Prepend First
  2. Constants
  3. Initializer
  4. Public methods
  5. Protected methods
  6. Private methods

It's also very easy to extend the cop and include new rules in the middle.

The basic configuration says:

Layout/ClassStructure:
  Enabled: false
  Categories:
    module_inclusion:
      - include
      - prepend
      - extend
  ExpectedOrder:
      - module_inclusion
      - constants
      - public_class_methods
      - initializer
      - instance_methods
      - protected_methods
      - private_methods

Lets imagine you got sad about people saying validates after define methods and also mess with other macros from ActiveRecord.

Lets say we want to have strict rules in Rails models and use the following order:

  1. Include, Extend or Prepend First
  2. Constants
  3. Attributes (attribute, attr_accessor, attr_reader, attr_writer)
  4. Associations (belongs_to, has_many, has_and_belongs_to_many ...)
  5. Validations (validate, validates_presence_of, validates_uniqueness_of ...)
  6. Hooks (before_save, after_save, after_initialize ...)
  7. Initializer
  8. Public methods
  9. Protected methods
  10. Private methods

Now we need to setup Categories and include them in the ExpectedOrder.

Layout/ClassStructure:
  Enabled: true
  Categories:
    module_inclusion:
      - include
      - prepend
      - extend
    attributes:
      - attribute
      - attr_reader
      - attr_writer
      - attr_accessor
    associations:
      - has_one
      - has_many
      - belongs_to
      - has_and_belongs_to_many
    validations:
      - validate
      - validates_presence_of
      - validates_uniqueness_of
    hooks:
      - after_save
      - after_create
      - after_initialize
  ExpectedOrder:
      - module_inclusion
      - constants
      - attributes
      - associations
      - validations
      - hooks
      - public_class_methods
      - initializer
      - public_methods
      - protected_methods
      - private_methods

Now it's ready to be tested.

Lets use a example with a few mistakes:

class User

  validate :name, :email, presence: true

  attr_reader :temporary_orders

  validates_uniqueness_of :email

  def email_domain
    email.split('@').last
  end

  has_many :orders
  after_create :send_welcome_email

  belongs_to :location
end

It supports autocorrect, and running it you can check that RuboCop has a kind of loop to keep autocorrecting until it's perfect.

user.rb:3:3: C: [Corrected] Layout/ClassStructure: attributes is supposed to appear before associations.
  attr_reader :temporary_orders
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
user.rb:3:3: C: [Corrected] Layout/ClassStructure: attributes is supposed to appear before validations.
  attr_reader :temporary_orders
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
user.rb:5:3: C: [Corrected] Layout/ClassStructure: associations is supposed to appear before hooks.
  belongs_to :location
  ^^^^^^^^^^^^^^^^^^^^
user.rb:5:3: C: [Corrected] Layout/ClassStructure: associations is supposed to appear before validations.
  has_many :orders
  ^^^^^^^^^^^^^^^^
user.rb:6:3: C: [Corrected] Layout/ClassStructure: associations is supposed to appear before validations.
  belongs_to :location
  ^^^^^^^^^^^^^^^^^^^^
user.rb:6:3: C: [Corrected] Layout/ClassStructure: validations is supposed to appear before hooks.
  validate :name, :email, presence: true
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
user.rb:8:3: C: [Corrected] Layout/ClassStructure: validations is supposed to appear before hooks.
  validates_uniqueness_of :email
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This feature is very cool because allow the cops algorithm simply execute one swap between the nodes that are not in the proper place. Then you can see it in action recursively until the file is totally organized.

After autocorrect the file looks like this:

class User

  attr_reader :temporary_orders
  has_many :orders
  belongs_to :location
  validates_uniqueness_of :email
  validate :name, :email, presence: true
  after_create :send_welcome_email


  def email_domain
    email.split('@').last
  end
end

So, that is what this cop does. I hope this cop to be useful for the community and make our code classes more organized. If you're interested in the full history you can check my Pull Request here.


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Olá, sou o Jônatas Davi Paganini e esse é meu blog. Sou programador, tenho alguns projetos no github e escrevo livremente aqui no ideia.me.

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