-simgrid::xbt::signal<void(VirtualMachine&)> VirtualMachine::on_start;
-simgrid::xbt::signal<void(VirtualMachine&)> VirtualMachine::on_started;
-simgrid::xbt::signal<void(VirtualMachine&)> VirtualMachine::on_shutdown;
-simgrid::xbt::signal<void(VirtualMachine&)> VirtualMachine::on_suspend;
-simgrid::xbt::signal<void(VirtualMachine&)> VirtualMachine::on_resume;
-simgrid::xbt::signal<void(VirtualMachine&)> VirtualMachine::on_migration_start;
-simgrid::xbt::signal<void(VirtualMachine&)> VirtualMachine::on_migration_end;
+simgrid::xbt::signal<void(VirtualMachine const&)> VirtualMachine::on_start;
+simgrid::xbt::signal<void(VirtualMachine const&)> VirtualMachine::on_started;
+simgrid::xbt::signal<void(VirtualMachine const&)> VirtualMachine::on_shutdown;
+simgrid::xbt::signal<void(VirtualMachine const&)> VirtualMachine::on_suspend;
+simgrid::xbt::signal<void(VirtualMachine const&)> VirtualMachine::on_resume;
+simgrid::xbt::signal<void(VirtualMachine const&)> VirtualMachine::on_migration_start;
+simgrid::xbt::signal<void(VirtualMachine const&)> VirtualMachine::on_migration_end;