use forward declaration to treat the dependency of fragments

Examples/test-suite/cpp11_shared_ptr_upcast.i

@@ -9,9 +9,9 @@
 #include <vector>
 %}
 
-%include std_vector.i
-%include std_map.i
-%include std_shared_ptr.i
+%include <std_vector.i>
+%include <std_map.i>
+%include <std_shared_ptr.i>
 
 %{
 

Lib/ruby/rubystdcommon.swg

@@ -3,12 +3,11 @@
  * The Ruby classes, for C++
  * ------------------------------------------------------------ */
 %include <rubyclasses.swg>
+%include <rubystdcommon_forward.swg>
 
-%fragment("StdTraits","header",fragment="StdTraitsCommon")
+%fragment("StdTraits","header",fragment="StdTraitsCommon",fragment="StdTraitsForwardDeclaration")
 {
 
-%#define SWIG_RUBYSTDCOMMON
-
 namespace swig {  
   /*
     Traits that provides the from method

Lib/ruby/rubystdcommon_forward.swg

@@ -0,0 +1,14 @@
+%fragment("StdTraitsForwardDeclaration","header")
+{
+namespace swig {
+  template <class Type> struct traits_asptr;
+  template <class Type> struct traits_asval;
+  struct pointer_category;
+  template <class Type, class Category> struct traits_as;
+  template<class Type> struct traits_from;
+  template <class Type> struct noconst_traits;
+  template <class Type> swig_type_info* type_info();
+  template <class Type> const char* type_name();
+  template <class Type> VALUE from(const Type& val);
+}
+}

Lib/ruby/std_shared_ptr.i

@@ -1,16 +1,15 @@
 #define SWIG_SHARED_PTR_NAMESPACE std
 %include <boost_shared_ptr.i>
+%include <rubystdcommon_forward.swg>
 
 
- /*
-  * We want to put the following code after the fragment "StdTraits" at rubystdcommon.swg.
-  * This code is needed if and only if the fragment and this std_shared_ptr.i are included at the same time.
-  * They don't always require each other. The order of including them is not predetermined either.
-  * So specifying the dependecy by using %fragment does not work.
-  */
-%wrapper %{
-#ifdef SWIG_RUBYSTDCOMMON
+%fragment("StdSharedPtrTraits","header",fragment="StdTraitsForwardDeclaration")
+{
 namespace swig {
+  /*
+   template specialization for functions defined in rubystdcommon.swg.
+   here we should treat smart pointers in a way different from the way we treat raw pointers.
+  */
   template <class Type>
   struct traits_asptr<std::shared_ptr<Type> > {
     static int asptr(VALUE obj, std::shared_ptr<Type> **val) {
@@ -84,6 +83,11 @@ namespace swig {
     }
   };
 
+  /*
+   we have to remove the const qualifier to work around a BUG
+   SWIG_TypeQuery("std::shared_ptr<const Type>") == NULL,
+   which is caused by %template treating const qualifiers not properly.
+  */
   template<class Type>
   struct traits_from<std::shared_ptr<const Type> > {
     static VALUE from(const std::shared_ptr<const Type>& val) {
@@ -92,5 +96,7 @@ namespace swig {
     }
   };
 }
-#endif
-%}
+}
+
+//force the fragment.
+%fragment("StdSharedPtrTraits");