Making friends...

gtsam_unstable/nonlinear/Expression.h

@@ -27,8 +27,13 @@
 #include <boost/range/adaptor/map.hpp>
 #include <boost/range/algorithm.hpp>
 
+class ExpressionFactorShallowTest;
+
 namespace gtsam {
 
+// Forward declare
+template<typename T> class ExpressionFactor;
+
 /**
  * Expression class that supports automatic differentiation
  */
@@ -204,6 +209,10 @@ private:
     return value;
   }
 
+  // be very selective on who can access these private methods:
+  friend class ExpressionFactor<T>;
+  friend class ::ExpressionFactorShallowTest;
+
 };
 
 // http://stackoverflow.com/questions/16260445/boost-bind-to-operator