Make data member private

Author: reuk

src/goto-diff/unified_diff.h

@@ -53,7 +53,6 @@ class unified_difft
     const irep_idt &function,
     goto_program_difft &dest) const;
 
-protected:
   const goto_functionst &old_goto_functions;
   const namespacet ns_old;
   const goto_functionst &new_goto_functions;
@@ -62,8 +61,6 @@ class unified_difft
   typedef std::vector<differencet> differencest;
   typedef std::map<irep_idt, differencest> differences_mapt;
 
-  differences_mapt differences_map_;
-
   void unified_diff(
     const irep_idt &identifier,
     const goto_programt &old_goto_program,
@@ -105,6 +102,9 @@ class unified_difft
          *ins2.get_target(),
          false));
   }
+
+private:
+  differences_mapt differences_map_;
 };
 
 #endif // CPROVER_GOTO_DIFF_UNIFIED_DIFF_H