+
+namespace s4u {
+class Activity;
+
+class Actor;
+/** Smart pointer to a simgrid::s4u::Actor */
+typedef boost::intrusive_ptr<Actor> ActorPtr;
+XBT_PUBLIC void intrusive_ptr_release(Actor* actor);
+XBT_PUBLIC void intrusive_ptr_add_ref(Actor* actor);
+
+class Barrier;
+/** Smart pointer to a simgrid::s4u::Barrier */
+typedef boost::intrusive_ptr<Barrier> BarrierPtr;
+XBT_PUBLIC void intrusive_ptr_release(Barrier* m);
+XBT_PUBLIC void intrusive_ptr_add_ref(Barrier* m);
+
+class Comm;
+/** Smart pointer to a simgrid::s4u::Comm */
+typedef boost::intrusive_ptr<Comm> CommPtr;
+XBT_PUBLIC void intrusive_ptr_release(Comm* c);
+XBT_PUBLIC void intrusive_ptr_add_ref(Comm* c);
+
+class ConditionVariable;
+/** Smart pointer to a simgrid::s4u::ConditionVariable */
+typedef boost::intrusive_ptr<ConditionVariable> ConditionVariablePtr;
+XBT_PUBLIC void intrusive_ptr_release(ConditionVariable* c);
+XBT_PUBLIC void intrusive_ptr_add_ref(ConditionVariable* c);
+
+class Engine;
+
+class Exec;
+/** Smart pointer to a simgrid::s4u::Exec */
+typedef boost::intrusive_ptr<Exec> ExecPtr;
+XBT_PUBLIC void intrusive_ptr_release(Exec* e);
+XBT_PUBLIC void intrusive_ptr_add_ref(Exec* e);
+class ExecSeq;
+class ExecPar;
+
+class Host;
+
+class Io;
+/** Smart pointer to a simgrid::s4u::Io */
+typedef boost::intrusive_ptr<Io> IoPtr;
+XBT_PUBLIC void intrusive_ptr_release(Io* i);
+XBT_PUBLIC void intrusive_ptr_add_ref(Io* i);
+
+class Link;
+
+class Mailbox;
+
+class Mutex;
+XBT_PUBLIC void intrusive_ptr_release(Mutex* m);
+XBT_PUBLIC void intrusive_ptr_add_ref(Mutex* m);
+/** Smart pointer to a simgrid::s4u::Mutex */
+typedef boost::intrusive_ptr<Mutex> MutexPtr;
+
+class NetZone;
+class VirtualMachine;
+class File;
+
+class Semaphore;
+/** Smart pointer to a simgrid::s4u::Semaphore */
+typedef boost::intrusive_ptr<Semaphore> SemaphorePtr;
+XBT_PUBLIC void intrusive_ptr_release(Semaphore* m);
+XBT_PUBLIC void intrusive_ptr_add_ref(Semaphore* m);
+
+class Storage;
+} // namespace s4u
+
+namespace config {
+template <class T> class Flag;
+}
+