Issues #276, #1163 - introduce class IncomingParam

src/plugin/COM_Value.h

Index: src/plugin/COM_Value.h
===================================================================
--- a/src/plugin/COM_Value.h
+++ b/src/plugin/COM_Value.h
@@ -115,6 +115,48 @@
        */
       BSTR_Argument& operator=(BSTR_Argument&&);   // = delete
     };
+
+    /**
+     * Constructor class for [in] parameters arriving from our COM entry points.
+     *
+     * The life cycle of a VARIANT value that comes to us as an [in] parameter is entirely managed by the caller.
+     * Thus the responsbilities of this class are for type checking and value conversion,
+     *   but not life cycle mangement.
+     *
+     * This class is specifically for use within COM server functions such as for IDispatch::Invoke.
+     *
+     * \par Status
+     *   This class is, in part, written for issue #1163 "Clean up IDispatch::Invoke implementations".
+     *   
+     */
+    class IncomingParam
+    {
+      /**
+       * The underlying variant value.
+       *
+       * It's stored as received and does receive any life cycle treatment.
+       */
+      VARIANT var;
+
+    public:
+      IncomingParam( VARIANT v )
+        : var( v )
+      {
+      }
+
+      /**
+       * Predicate whether the variant is convertible to std::wstring.
+       *
+       * This predicate incorporates both type compatibility and implementation support.
+       * Some types that could be converted are not, simply because they're not used in the present code base.
+       */
+      bool wstringConvertible() const;
+
+      /**
+       * Convert variant to std::wstring and if not convertible return the empty string.
+       */
+      std::wstring wstringValueNoexcept() const;
+    };
   }
 }