https://github.com/basecamp/concerning
Bite-sized separation of concerns
https://github.com/basecamp/concerning
ruby
Last synced: 7 months ago
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Bite-sized separation of concerns
- Host: GitHub
- URL: https://github.com/basecamp/concerning
- Owner: basecamp
- License: mit
- Archived: true
- Created: 2013-07-02T18:17:27.000Z (over 12 years ago)
- Default Branch: master
- Last Pushed: 2023-03-16T01:18:02.000Z (almost 3 years ago)
- Last Synced: 2025-07-10T16:09:30.590Z (7 months ago)
- Topics: ruby
- Language: Ruby
- Homepage:
- Size: 17.6 KB
- Stars: 202
- Watchers: 38
- Forks: 5
- 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.