Make Twitter::NullObject Comparable

Closes sferik/t-ruby#232.

lib/twitter/null_object.rb

@@ -2,11 +2,33 @@
 
 module Twitter
   NullObject = Naught.build do |config|
+    include Comparable
+
     config.black_hole
     config.define_explicit_conversions
     config.define_implicit_conversions
     config.predicates_return false
 
+    def instance_of?(klass)
+      raise(TypeError.new("class or module required")) unless klass.is_a?(Class)
+      self.class == klass
+    end
+
+    def kind_of?(mod)
+      raise(TypeError.new("class or module required")) unless mod.is_a?(Module)
+      self.class.ancestors.include?(mod)
+    end
+
+    alias_method :is_a?, :kind_of?
+
+    def <=>(other)
+      if other.is_a?(self.class)
+        0
+      else
+        -1
+      end
+    end
+
     def nil?
       true
     end

spec/twitter/null_object_spec.rb

@@ -0,0 +1,90 @@
+require 'helper'
+
+describe Twitter::NullObject do
+
+  describe '#instance_of?' do
+    it 'returns true for Twitter::NullObject' do
+      expect(subject.instance_of?(Twitter::NullObject)).to be true
+    end
+    it 'returns false for other classes' do
+      expect(subject.instance_of?(String)).to be false
+    end
+  end
+
+  describe '#kind_of?' do
+    it 'returns true for Twitter::NullObject' do
+      expect(subject).to be_a Twitter::NullObject
+    end
+    it 'returns true for module ancestors' do
+      expect(subject).to be_a Comparable
+    end
+    it 'returns true for class ancestors' do
+      expect(subject).to be_a Naught::BasicObject
+    end
+    it 'returns false for non-ancestors' do
+      expect(subject).not_to be_a String
+    end
+  end
+
+  describe '#<=>' do
+    it 'sorts before non-null objects' do
+      expect(subject <=> 1).to eq(-1)
+    end
+    it 'is equal to other Twitter::NullObjects' do
+      null_object1 = Twitter::NullObject.new
+      null_object2 = Twitter::NullObject.new
+      expect(null_object1 <=> null_object2).to eq(0)
+    end
+  end
+
+  describe '#nil?' do
+    it 'returns true' do
+      expect(subject).to be_nil
+    end
+  end
+
+  describe 'black hole' do
+    it 'returns self for missing methods' do
+      expect(subject.missing).to eq(subject)
+    end
+  end
+
+  describe 'explicit conversions' do
+    describe '#to_a' do
+      it 'returns []' do
+        expect(subject.to_a).to eq([])
+      end
+    end
+    describe '#to_s' do
+      it 'returns ""' do
+        expect(subject.to_s).to eq("")
+      end
+    end
+  end
+
+  describe 'implicit conversions' do
+    describe '#to_ary' do
+      it 'returns []' do
+        expect(subject.to_ary).to eq([])
+      end
+    end
+    describe '#to_str' do
+      it 'returns ""' do
+        expect(subject.to_str).to eq("")
+      end
+    end
+  end
+
+  describe 'predicates' do
+    it 'return false for missing methods' do
+      expect(subject.missing?).to be false
+    end
+  end
+
+  describe 'predicates' do
+    it 'return false for missing methods' do
+      expect(subject.missing?).to be false
+    end
+  end
+
+end