Add "is_null" for boxed_values to see if they contain a null shared_ptr value

include/chaiscript/dispatchkit/bootstrap.hpp

@@ -709,6 +709,7 @@ namespace chaiscript
         m->eval("def Dynamic_Object::clone() { var new_o := Dynamic_Object(this.get_type_name()); for_each(this.get_attrs(), bind(fun(new_o, x) { new_o.get_attr(x.first) = x.second; }, new_o, _) ); return new_o; }");
 
         m->add(fun(&Boxed_Value::is_undef), "is_undef");
+        m->add(fun(&Boxed_Value::is_null), "is_null");
 
         basic_constructors<bool>("bool", m);
         oper_assign<std::string>(m);

include/chaiscript/dispatchkit/boxed_value.hpp

@@ -49,12 +49,20 @@ namespace chaiscript
             return ptr->unique();
           }
 
+        template<typename T>
+          static bool is_null(boost::any *a)
+          {
+            boost::shared_ptr<T> *ptr = boost::any_cast<boost::shared_ptr<T> >(a);
+            return ptr->get() == 0;
+          }
+
         Data(const Type_Info &ti,
             const boost::any &to,
             bool tr,
-            const boost::function<bool (boost::any*)> &t_unique = boost::function<bool (boost::any*)>())
+            const boost::function<bool (boost::any*)> &t_unique = boost::function<bool (boost::any*)>(),
+            const boost::function<bool (boost::any*)> &t_is_null = boost::function<bool (boost::any*)>())
           : m_type_info(ti), m_obj(to), 
-          m_is_ref(tr), m_unique(t_unique)
+          m_is_ref(tr), m_unique(t_unique), m_is_null(t_is_null)
         {
         }
 
@@ -64,6 +72,7 @@ namespace chaiscript
           m_obj = rhs.m_obj;
           m_is_ref = rhs.m_is_ref;
           m_unique = rhs.m_unique;
+          m_is_null = rhs.m_is_null;
 
           return *this;
         }
@@ -72,6 +81,7 @@ namespace chaiscript
         boost::any m_obj;
         bool m_is_ref;
         boost::function<bool (boost::any*)> m_unique;
+        boost::function<bool (boost::any*)> m_is_null;
       };
 
       /**
@@ -111,7 +121,8 @@ namespace chaiscript
                   detail::Get_Type_Info<T>::get(), 
                   boost::any(obj), 
                   false,
-                  &Data::unique<T>)
+                  &Data::unique<T>,
+                  &Data::is_null<T>)
                 );
 
             std::map<std::pair<const void *, bool>, Data>::iterator itr
@@ -170,7 +181,8 @@ namespace chaiscript
                   detail::Get_Type_Info<T>::get(), 
                   boost::any(boost::shared_ptr<T>(new T(t))), 
                   false,
-                  &Data::unique<T>)
+                  &Data::unique<T>,
+                  &Data::is_null<T>)
                 );
 
             boost::shared_ptr<T> *ptr = boost::any_cast<boost::shared_ptr<T> >(&data->m_obj);
@@ -217,7 +229,7 @@ namespace chaiscript
           }
         }
 
-        std::map<std::pair<const void *, bool>, Data > m_ptrs;
+        std::map<std::pair<const void *, bool>, Data> m_ptrs;
         int m_cullcount;
       };
 
@@ -298,6 +310,16 @@ namespace chaiscript
         return m_data->m_type_info.is_undef();
       }
 
+      bool is_null() const
+      {
+        if (m_data->m_is_null)
+        {
+          return m_data->m_is_null(&m_data->m_obj);
+        } else {
+          return false;
+        }
+      }
+
       boost::any get() const
       {
         return m_data->m_obj;

src/example.cpp

@@ -110,7 +110,7 @@ int main(int argc, char *argv[]) {
 
   //Finally, it is possible to register any boost::function as a system function, in this 
   //way, we can, for instance add a bound member function to the system
-  chai.add(fun(&System::do_callbacks, boost::ref(system), "Bound Test"), "do_callbacks");
+  chai.add(fun(&System::do_callbacks, boost::ref(system), std::string("Bound Test")), "do_callbacks");
 
   //Call bound version of do_callbacks
   chai("do_callbacks()");
@@ -143,6 +143,8 @@ int main(int argc, char *argv[]) {
 
   log("Functor test output", boost::lexical_cast<std::string>(x));
 
+  chai.add(var(boost::shared_ptr<int>()), "nullvar");
+  chai("print(\"This should be true.\"); print(nullvar.is_null())");
 
   //Ability to create our own container types when needed. std::vector and std::map are
   //mostly supported currently