Decoration in Ruby should be easy. With
BasicDecorator, it is.
Add this line to your application's Gemfile:
And then execute:
Or install it yourself as:
$ gem install basic_decorator
Decorators are a wonderful design pattern allowing a developer to modify,
extend, or otherwise change the behavior of an object while maintaining its
interface. Remember ActiveSupport's
alias_method_chain? That was essentially
an inline (bastardized) decoration that mutated the object. If you want to
read about the Decorator pattern, I suggest you check out:
Knowing about decorators, where does
BasicDecorator fall? How do you use it?
Your decorators inherit from
BasicDecorator::Decorator and you'll have
access to the instance variable
@component, the object passed in to the
Let's start off with the common 'Coffee', 'Cream', and 'Sugar' example. Here's
our first object,
class Coffee def cost Money.new(250, 'USD') end def origin 'Columbia' end def additional_ingredients  end end
Fairly straightforward. Let's write up decorators for
class Cream < BasicDecorator::Decorator def cost @component.cost + ::Money.new(75, 'USD') end def additional_ingredients @component.additional_ingredients + ['Cream'] end end class Sugar < BasicDecorator::Decorator def cost @component.cost + ::Money.new(25, 'USD') end def additional_ingredients @component.additional_ingredients + ['Sugar'] end end
If a method isn't defined on the decorator, it gets delegated to the
method_missing), meaning it'll keep your decorators nice
and thin; only define the methods of whom you want to change the behavior.
Cream may decorate
Coffee any number of times.
coffee = Coffee.new # #<Coffee:0x007fb78a8c5ae8> tasty_coffee = Sugar.new(Cream.new(coffee)) # #<Coffee:0x007fb78a8c5ae8> coffee.cost # #<Money cents:250 currency:USD> tasty_coffee.cost # #<Money cents:350 currency:USD> coffee.additional_ingredients #  tasty_coffee.additional_ingredients # ["Cream", "Sugar"] tasty_coffee.is_a? Coffee # true
You may want to be careful of decorating objects like arrays. Decoration typically won't mutate the component you're decorating; again, just something to be aware of.
- Fork it
- Create your feature branch (
git checkout -b my-new-feature)
- Commit your changes (
git commit -am 'Added some feature')
- Push to the branch (
git push origin my-new-feature)
- Create new Pull Request
Written 2012 by Josh Clayton
Check the LICENSE