https://github.com/basecamp/concerning

Bite-sized separation of concerns
https://github.com/basecamp/concerning

ruby

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Bite-sized separation of concerns

• Host: GitHub
• URL: https://github.com/basecamp/concerning
• Owner: basecamp
• License: mit
• Created: 2013-07-02T18:17:27.000Z (over 11 years ago)
• Default Branch: master
• Last Pushed: 2023-03-16T01:18:02.000Z (over 1 year ago)
• Last Synced: 2024-07-20T17:24:12.688Z (4 months ago)
• Topics: ruby
• Language: Ruby
• Homepage:
• Size: 17.6 KB
• Stars: 202
• Watchers: 38
• Forks: 6
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • License: MIT-LICENSE

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README

        
## Bite-sized separation of concerns

(*Note!* Module#concerning is included in Rails 4.1. You can still use this

library, but it will defer to Active Support's implementation if available.)

We often find ourselves with a medium-sized chunk of behavior that we'd

like to extract, but only mix in to a single class.

Extracting a plain old Ruby object to encapsulate it and collaborate or

delegate to the original object is often a good choice, but when there's

no additional state to encapsulate or we're making DSL-style declarations

about the parent class, introducing new collaborators can obfuscate rather

than simplify.

The typical route is to just dump everything in a monolithic class, perhaps

with a comment, as a least-bad alternative. Using modules in separate files

means tedious sifting to get a big-picture view.

## Dissatisfying ways to separate small concerns

#### Using comments:

```ruby

class Todo

  # Other todo implementation

  # ...

  ## Event tracking

  has_many :events

  before_create :track_creation

  after_destroy :track_deletion

  def self.next_by_event

    # ...

  end

  private

    def track_creation

      # ...

    end

end

```

#### With an inline module:

Noisy syntax.

```ruby

class Todo

  # Other todo implementation

  # ...

  module EventTracking

    extend ActiveSupport::Concern

    included do

      has_many :events

      before_create :track_creation

      after_destroy :track_deletion

    end

    module ClassMethods

      def next_by_event

        # ...

      end

    end

    private

      def track_creation

        # ...

      end

  end

  include EventTracking

end

```

#### Mix-in noise exiled to its own file:

Once our chunk of behavior starts pushing the scroll-to-understand it

boundary, we give in and move it to a separate file. At this size, the

overhead feels in good proportion to the size of our extraction, despite

diluting our at-a-glance sense of how things really work.

```ruby

class Todo

  # Other todo implementation

  # ...

  include TodoEventTracking

end

```

## Introducing Module#concerning

By quieting the mix-in noise, we arrive at a natural, low-ceremony way to

separate bite-sized concerns.

```ruby

  class Todo

    # Other todo implementation

    # ...

    concerning :EventTracking do

      included do

        has_many :events

        before_create :track_creation

        after_destroy :track_deletion

      end

      class_methods do

        def next_by_event

          # ...

        end

      end

      private

        def track_creation

          # ...

        end

    end

  end

  Todo.ancestors

  # => Todo, Todo::EventTracking, Object

```

This small step has some wonderful ripple effects. We can

* grok the behavior of our class in one glance,

* clean up monolithic junk-drawer classes by separating their concerns, and

* stop leaning on protected/private for crude "this is internal stuff" modularity.