Pull the file setter into a separate object

lib/paperclip.rb

@@ -51,6 +51,7 @@ require 'paperclip/missing_attachment_styles'
 require 'paperclip/validators'
 require 'paperclip/logger'
 require 'paperclip/helpers'
+require 'paperclip/has_attached_file'
 require 'paperclip/tasks/attachments'
 require 'mime/types'
 require 'logger'
@@ -173,17 +174,24 @@ module Paperclip
     #     end
     #   end
     def has_attached_file(name, options = {})
+      HasAttachedFile.new(name, options).define_on(self)
+
       options = Paperclip::AttachmentOptions.new(options)
       Paperclip.classes_with_attachments << self.name
       Paperclip.check_for_path_clash(name, options[:path], self.name)
 
+      Paperclip::Tasks::Attachments.add(self, name, options)
+
       after_save { send(name).send(:save) }
       before_destroy { send(name).send(:queue_all_for_delete) }
       after_destroy { send(name).send(:flush_deletes) }
 
       define_paperclip_callbacks :post_process, :"#{name}_post_process"
 
-      Paperclip::Tasks::Attachments.add(self, name, options)
+      validates_each(name) do |record, attr, value|
+        attachment = record.send(name)
+        attachment.send(:flush_errors)
+      end
 
       define_method name do |*args|
         ivar = "@attachment_#{name}"
@@ -201,18 +209,9 @@ module Paperclip
         end
       end
 
-      define_method "#{name}=" do |file|
-        send(name).assign(file)
-      end
-
       define_method "#{name}?" do
         send(name).file?
       end
-
-      validates_each(name) do |record, attr, value|
-        attachment = record.send(name)
-        attachment.send(:flush_errors)
-      end
     end
   end
 end

lib/paperclip/has_attached_file.rb

+module Paperclip
+  class HasAttachedFile
+    def initialize(name, options)
+      @name = name
+    end
+
+    def define_on(klass)
+      name = @name
+      klass.send :define_method, "#{@name}=" do |file|
+        send(name).assign(file)
+      end
+    end
+  end
+end

test/has_attached_file_test.rb

+require './test/helper'
+require 'paperclip/has_attached_file'
+
+class HasAttachedFileTest < Test::Unit::TestCase
+  context '#define_on' do
+    should 'define a setter on the class object' do
+      a_class = stub('class', define_method: nil)
+      has_attached_file = Paperclip::HasAttachedFile.new(:avatar, {})
+
+      has_attached_file.define_on(a_class)
+
+      assert_received(a_class, :define_method) do |expect|
+        expect.with('avatar=')
+      end
+    end
+  end
+end

test/tasks/attachments_test.rb

 require './test/helper'
-require 'tasks/attachments'
+require 'paperclip/tasks/attachments'
 
 class AttachmentsTest < Test::Unit::TestCase
   context '.names_for' do