H5Utils::hist::HistogramMerger Node1 H5Utils::hist::Histogram Merger   + ~HistogramMerger() + add() + write() - make() Node2 std::map< std::string, std::unique_ptr< H5Utils ::hist::IHistogram > >     Node2->Node1 -m_hists Node3 std::string     Node3->Node2 +keys Node4 std::basic_string< Char >     Node4->Node3 Node5 std::unique_ptr< H5Utils ::hist::IHistogram >   + operator->() Node5->Node2 +elements Node6 H5Utils::hist::IHistogram   + ~IHistogram() + add() + write() Node6->Node5 +ptr