NullObject

Null Object Design Pattern Ruby implementation

Intent

The intent of a Null Object is to encapsulate the absence of an object by providing a substitutable alternative that offers suitable default do nothing behavior. In short, a design where “nothing will come of nothing”

More about Null Object Pattern you can find here:

• http://en.wikipedia.org/wiki/Null_Object_pattern
• http://sourcemaking.com/design_patterns/null_object
• http://avdi.org/devblog/2011/05/30/null-objects-and-falsiness

See also the avdi/naught gem for extended variations of the null object pattern for Ruby 1.9.

Usage

# examples from http://avdi.org/devblog/2011/05/30/null-objects-and-falsiness/

Null::Object.instance.foobar.baz.buz

def Maybe(value)
  case value
  when nil then Null::Object.instance
  else value
  end
end

def slug(title)
  Maybe(title).strip.downcase.tr('^[0-9a-z]', '-')
end

h = {}

slug(h[:missing_key]) # => ""

foo = Null::Object.instance

foo.to_s # => ""
foo.to_a # => []
foo.to_i # => 0
foo.to_f # => 0.0
foo.nil? # => true

# Custom Null Object

class FooNullObject
  include Null

  def to_bar
    "nothing here"
  end
end

foo = FooNullObject.instance
foo.to_bar # => "nothing here"
foo.to_s   # => ""

Setup

If you are using bundler add nullobject to your Gemfile:

gem 'nullobject'

Then run:

bundle install

Otherwise install the gem:

gem install nullobject

and require it in your project:

require 'nullobject'

Development

Source hosted at GitHub. Report Issues/Feature requests on GitHub Issues.

Tests can be ran with rake test

Note on Patches/Pull Requests

• Fork the project.
• Make your feature addition or bug fix.
• Add tests for it. This is important so I don't break it in a future version unintentionally.
• Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
• Send me a pull request. Bonus points for topic branches.

Copyright

Copyright (c) 2012 Marcin Ciunelis. See LICENSE for details.