Moved the business of interpolation into the interpolations module

lib/paperclip/attachment.rb

@@ -388,12 +388,7 @@ module Paperclip
     end
 
     def interpolate pattern, style = default_style #:nodoc:
-      interpolations = Paperclip::Interpolations.all
-      interpolations.reverse.inject( pattern.dup ) do |result, tag|
-        result.gsub(/:#{tag}/) do |match|
-          Paperclip::Interpolations.send( tag, self, style )
-        end
-      end
+      Paperclip::Interpolations.interpolate(pattern, self, style)
     end
 
     def queue_existing_for_delete #:nodoc:

lib/paperclip/interpolations.rb

@@ -14,6 +14,14 @@ module Paperclip
       self.instance_methods(false).sort
     end
 
+    def self.interpolate pattern, *args
+      all.reverse.inject( pattern.dup ) do |result, tag|
+        result.gsub(/:#{tag}/) do |match|
+          send( tag, *args )
+        end
+      end
+    end
+
     def rails_root attachment, style
       RAILS_ROOT
     end

test/interpolations_test.rb

@@ -75,4 +75,12 @@ class InterpolationsTest < Test::Unit::TestCase
     attachment.expects(:default_style).returns(:default_style)
     assert_equal :default_style, Paperclip::Interpolations.style(attachment, nil)
   end
+
+  should "call all expected interpolations with the given arguments" do
+    Paperclip::Interpolations.expects(:id).with(:attachment, :style).returns(1234)
+    Paperclip::Interpolations.expects(:attachment).with(:attachment, :style).returns("attachments")
+    Paperclip::Interpolations.expects(:notreal).never
+    value = Paperclip::Interpolations.interpolate(":notreal/:id/:attachment", :attachment, :style)
+    assert_equal ":notreal/1234/attachments", value
+  end
 end