namespace s4u {
xbt::signal<void(Storage&)> Storage::on_creation;
-xbt::signal<void(Storage&)> Storage::on_destruction;
-xbt::signal<void(Storage&)> Storage::on_state_change;
+xbt::signal<void(Storage const&)> Storage::on_destruction;
+xbt::signal<void(Storage const&)> Storage::on_state_change;
Storage::Storage(const std::string& name, kernel::resource::StorageImpl* pimpl) : pimpl_(pimpl), name_(name)
{