-xbt::signal<void(ActorPtr)> s4u::Actor::on_creation;
-xbt::signal<void(ActorPtr)> s4u::Actor::on_suspend;
-xbt::signal<void(ActorPtr)> s4u::Actor::on_resume;
-xbt::signal<void(ActorPtr)> s4u::Actor::on_sleep;
-xbt::signal<void(ActorPtr)> s4u::Actor::on_wake_up;
-xbt::signal<void(ActorPtr)> s4u::Actor::on_migration_start;
-xbt::signal<void(ActorPtr)> s4u::Actor::on_migration_end;
-xbt::signal<void(ActorPtr)> s4u::Actor::on_destruction;
+xbt::signal<void(Actor&)> s4u::Actor::on_creation;
+xbt::signal<void(Actor const&)> s4u::Actor::on_suspend;
+xbt::signal<void(Actor const&)> s4u::Actor::on_resume;
+xbt::signal<void(Actor const&)> s4u::Actor::on_sleep;
+xbt::signal<void(Actor const&)> s4u::Actor::on_wake_up;
+xbt::signal<void(Actor const&)> s4u::Actor::on_migration_start;
+xbt::signal<void(Actor const&)> s4u::Actor::on_migration_end;
+xbt::signal<void(Actor const&)> s4u::Actor::on_destruction;