They're used to implement perfect forwarding: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm http://www.open-std.org/jtc1/sc22/wg21/docs/pape

They're used to implement perfect forwarding: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n138...