...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::pointer_plus_bit
template<typename Pointer> struct pointer_plus_bit { static const bool value; };
This is class that is supposed to have static methods to embed an extra bit of information in a pointer. This is a declaration and there is no default implementation, because operations to embed the bit change with every pointer type.
An implementation that detects that a pointer type whose has_pointer_plus_bit<>::value is non-zero can make use of these operations to embed the bit in the pointer.