Allow retrieval of uploader index within uploaders. Closes #1771

lib/carrierwave/uploader/mountable.rb

@@ -33,6 +33,12 @@ def initialize(model=nil, mounted_as=nil)
         @mounted_as = mounted_as
       end
 
+      ##
+      # Returns array index of given uploader within currently mounted uploaders
+      #
+      def index
+        model.__send__(:_mounter, mounted_as).uploaders.index(self)
+      end
     end # Mountable
   end # Uploader
 end # CarrierWave

spec/uploader/mountable_spec.rb

@@ -23,4 +23,17 @@
       expect(uploader.mounted_as).to eq(:llama)
     end
   end
+
+  describe '#index' do
+    let(:model) { Class.new.send(:extend, CarrierWave::Mount) }
+    let(:instance) { model.new }
+    before do
+      model.mount_uploaders(:images, uploader_class)
+      instance.images = [stub_file('test.jpg'), stub_file('bork.txt')]
+    end
+
+    it "returns the current index in uploaders" do
+      expect(instance.images.map(&:index)).to eq [0, 1]
+    end
+  end
 end