-xbt::signal<void()> on_platform_creation;
-xbt::signal<void()> on_platform_created;
-xbt::signal<void()> on_simulation_end;
-xbt::signal<void(double)> on_time_advance;
-xbt::signal<void(void)> on_deadlock;
+xbt::signal<void()> Engine::on_platform_creation;
+xbt::signal<void()> Engine::on_platform_created;
+xbt::signal<void()> Engine::on_simulation_end;
+xbt::signal<void(double)> Engine::on_time_advance;
+xbt::signal<void(void)> Engine::on_deadlock;