diff --git a/src/lib/diff/record-content-mutator.hpp b/src/lib/diff/record-content-mutator.hpp
index 5ede5259f..5f672e557 100644
--- a/src/lib/diff/record-content-mutator.hpp
+++ b/src/lib/diff/record-content-mutator.hpp
@@ -57,19 +57,54 @@ namespace diff{
   
   /** @internal helper for DiffApplicationStrategy<Rec::Mutator> */
   template<class STO>
-  class RecordContentMutator
+  struct RecordContentMutator
     : boost::noncopyable
     {
-    public:
-      explicit
+      using Iter = typename STO::iterator;
+      
+      STO attribs;
+      STO children;
+      Iter pos;
+      
       RecordContentMutator()
+        : attribs()
+        , children()
+        , pos(attribs.begin())
+        { }
+      
+      
+      bool
+      empty()  const
         {
-          swap (attribs_, target_.attribs());
-          swap (children_, target_.children());
-          
-          // heuristics for storage pre-allocation
-          target_.attribs().reserve (attribs_.size() * 120 / 100);
-          target_.children().reserve (children_.size() * 120 / 100);
+          return attribs.empty()
+              && children.empty();
+        }
+      
+      bool
+      currIsAttrib()  const
+        {
+          UNIMPLEMENTED ("determine current scope");
+        }
+      
+      bool
+      currIsChild()  const
+        {
+          UNIMPLEMENTED ("determine current scope");
+        }
+      
+      Iter end()        { return children.end(); }
+      Iter end()  const { return children.end(); }
+      
+      RecordContentMutator&
+      operator++()
+        {
+          UNIMPLEMENTED ("iteration");
+        }
+      
+      void
+      resetPos()
+        {
+          pos = attribs.begin();
         }
     };
   
diff --git a/src/lib/diff/record.hpp b/src/lib/diff/record.hpp
index fbeaf0eef..457068ca7 100644
--- a/src/lib/diff/record.hpp
+++ b/src/lib/diff/record.hpp
@@ -92,6 +92,8 @@
 #include "lib/itertools.hpp"
 #include "lib/util.hpp"
 
+#include "lib/diff/record-content-mutator.hpp"
+
 #include <boost/noncopyable.hpp>
 
 #include <algorithm>
@@ -239,6 +241,8 @@ namespace diff{
        */
       class Mutator;
       
+      using ContentMutator = RecordContentMutator<Storage>;
+      
       
       /**
        * copy-initialise (or convert) from the given Mutator instance.
@@ -453,7 +457,12 @@ namespace diff{
       
       Storage& attribs()  { return record_.attribs_; }
       Storage& children() { return record_.children_; }
-      
+      void
+      swapContent (ContentMutator& alteredContent)
+        {
+          std::swap (record_.attribs_, alteredContent.attribs);
+          std::swap (record_.children_, alteredContent.children);
+        }
       
       /* === extension point for building specific value types === */
       /*
diff --git a/tests/library/diff/generic-record-update-test.cpp b/tests/library/diff/generic-record-update-test.cpp
index 92154774f..2767982a8 100644
--- a/tests/library/diff/generic-record-update-test.cpp
+++ b/tests/library/diff/generic-record-update-test.cpp
@@ -107,24 +107,27 @@ namespace test{
           mut.setType("🌰");
           std::cout << string(subject) << std::endl;
           
-          CHECK (!isnil (mut));
-          RecS::ContentMutator content = mut.swapContent();
+          RecS::ContentMutator content;
           
-          CHECK ( isnil (mut));
+          CHECK (!isnil (mut));
+          CHECK ( isnil (content));
+          mut.swapContent(content);
           CHECK (!isnil (content));
+          CHECK ( isnil (mut));
+          
           CHECK (content.pos == content.attribs.begin());
           CHECK (content.currIsAttrib());
           CHECK (!content.currIsChild());
           CHECK ("b = β" == *content.pos);
           
-          void* rawElm = &attribs[0];
+          void* rawElm = &content.attribs[0];
           swap (content.attribs[0], content.attribs[1]);
           CHECK ("a = α" == *content.pos);
-          CHECK (rawElm == content.pos);
+          CHECK (rawElm == & *content.pos);
           
           ++content;
           CHECK ("b = β" == *content.pos);
-          CHECK (rawElm != content.pos);
+          CHECK (rawElm != &*content.pos);
           CHECK (content.currIsAttrib());
           CHECK (!content.currIsChild());
           
@@ -148,18 +151,18 @@ namespace test{
           VERIFY_ERROR (ITER_EXHAUST, ++content);
           
           content.resetPos();
-          CHECK (rawElm == content.pos);
+          CHECK (rawElm == & *content.pos);
           ++content;
           CHECK ("b = β" == *content.pos);
           
           CHECK ( isnil (mut));
           CHECK (!isnil (content));
-          mut.swapContent();
+          mut.swapContent(content);
           CHECK ( isnil (content));
           CHECK (!isnil (mut));
           
           mut.replace(subject);
-          CHECK (Seq({"a = α", "b = β", "γ", "δ", "ε"}) == contents(a));
+          CHECK (Seq({"a = α", "b = β", "γ", "δ", "ε"}) == contents(subject));
           std::cout << string(subject) << std::endl;
         }
     };