http://www.boost.org/doc/libs/1_35_0/doc/html/intrusive/usage.html http://www.boost.org/doc/libs/1_35_0/doc/html/intrusive/usag... Not sure if this qualifies a

http://www.boost.org/doc/libs/1_35_0/doc/html/intrusive/usage.html http://www.boost.org/doc/libs/1_35_0/doc/html/intrusive/usag... Not sure if this qualifies as not "breaking encapsulation" but it's as close as you're going to get.