NilObject, much borrowed from avdi.org

nil_object.rb

class NilObject
  def true?;    false end
  def false?;   true end
  def nil?;     true end
  def blank?;   true end
  def present?; false end
  def empty?;   true end
  def to_s;     "" end
  def !;        true end

  def method_missing(*args, &block)
    self
  end

  def to_value
    nil
  end

  module Confidence
    def self.included(base)
      base.extend self
    end

    def Maybe(value)
      case value
      when nil then NilObject.new
      else value
      end
    end

    def Actual(object)
      case object
      when NilObject then nil
      else object
      end
    end
  end
end

nil_object_spec.rb

require 'spec_helper_base'
require 'nil_object'

class SomeObject
  include NilObject::Confidence

  attr_accessor :colour

  def self.maybe_edible; Maybe(nil) end
  def maybe_colour;      Maybe(colour) end
  def actual_colour;     Actual(colour) end
end

describe NilObject do
  its(:true?)    { should be_false }
  its(:false?)   { should be_true }
  its(:nil?)     { should be_true }
  its(:blank?)   { should be_true }
  its(:present?) { should be_false }
  its(:empty?)   { should be_true }
  its(:to_s)     { should == "" }

  it "is true when negated" do
    (!subject).should be_true
    (not subject).should be_true
  end

  it "returns nil for all chained methods" do
    subject.foo.bar.baz.should be_nil
  end
end

describe NilObject::Confidence do
  describe "Maybe" do
    subject { SomeObject.new }

    it "returns actual value when present" do
      subject.colour = "blue"
      subject.maybe_colour.should == "blue"
    end

    it "returns a NilObject for nil" do
      subject.colour = nil
      subject.maybe_colour.should be_a NilObject
    end
  end

  describe "Actual" do
    subject { SomeObject.new }

    it "returns actual value when present" do
      subject.colour = "red"
      subject.actual_colour.should == "red"
    end

    it "returns actual nil when nil" do
      subject.colour = nil
      subject.actual_colour.should be_a NilClass
    end
  end

  describe "class methods" do
    it "is extended" do
      SomeObject.maybe_edible.should be_a NilObject
    end
  end
end