Use a macro to convert Geef.Object to :geef_object

lib/geef/blob.ex

@@ -1,5 +1,6 @@
 defmodule Geef.Blob do
   alias Geef.Object
+  import :macros, Object
 
   def lookup(repo, id) do
     case :geef_obj.lookup(repo, id) do
@@ -11,11 +12,11 @@ defmodule Geef.Blob do
   end
 
   def size(obj = Object[type: :blob]) do
-    :geef_blob.size(set_elem(obj, 0, :geef_object))
+    :geef_blob.size(rebind(obj))
   end
 
   def content(obj = Object[type: :blob]) do
-    :geef_blob.content(set_elem(obj, 0, :geef_object))
+    :geef_blob.content(rebind(obj))
   end
 
 end