Although polymorphism is a recommended standard in Object-Oriented programming for invoking varied behavior in an inheritance hierarchy, sometimes it is still useful to verify if a particular model belongs to a certain type when the behavior concerned does not belong to the model and is too small to require a Design Pattern like Strategy.
A common example in Rails is checking user roles before rendering certain parts of the view:
<% if user.is_a?(Admin) %> <%= link_to 'Admin', admin_dashboard_path %> <% end %> <% if user.is_a?(Customer) %> <%= link_to 'Customer Profile', customer_profile_path %> <% end %>
To avoid the
model.is_a?(Admin) syntax, a more readable approach
that developers resort to is to add an English-like DSL method that hides the
details of Object-Oriented type checking:
The Rails example above would then become:
<% if user.admin? %> <%= link_to 'Admin', admin_dashboard_path %> <% end %> <% if user.customer? %> <%= link_to 'Customer Profile', customer_profile_path %> <% end %>
Implementing such methods manually gets repetitive and error-prone, so an easier
way to get these methods automatically is to mixin the
require 'easily_typable' # in IRB at cloned project directory, call this instead: require './lib/easily_typable' class Vehicle include EasilyTypable end class Car < Vehicle end class Truck < Vehicle end class Van < Vehicle end puts Car.new.vehicle? # prints true puts Car.new.car? # prints true puts Car.new.truck? # prints false puts Car.new.van? # prints false puts Truck.new.vehicle? # prints true puts Truck.new.car? # prints false puts Truck.new.truck? # prints true puts Truck.new.van? # prints false puts Van.new.vehicle? # prints true puts Van.new.car? # prints false puts Van.new.truck? # prints false puts Van.new.van? # prints true
- v1.0.2: Support namespaced subclasses
- v1.0.1: Rails model lazy loading now loads EasilyTypable methods automagically
- v1.0.0: Initial EasilyTypable implementation for Ruby
Contributing to EasilyTypable
- Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet.
- Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it.
- Fork the project.
- Start a feature/bugfix branch.
- Commit and push until you are happy with your contribution.
- Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
- Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.
- Copyright (c) 2009-2020 Andy Maleh
- See LICENSE.txt for further details.