...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::key_of_value
// In header: <boost/intrusive/options.hpp> template<typename KeyOfValue> struct key_of_value { };
This option setter specifies the a function object that specifies the type of the key of an associative container and an operator to obtain it from a value type.
This function object must the define a `key_type` and a member with signature `const key_type & operator()(const value_type &) const` that will return the key from a value_type of an associative container