...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::intrusive::optimize_multikey_is_true::two_or_three
// In header: <boost/intrusive/hashtable.hpp> template<bool Add> struct two_or_three { // public data members unspecified _; };