...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::xpressive::at — at
is a lazy PolymorphicFunctionObject for indexing into a sequence in an xpressive semantic action.
// In header: <boost/xpressive/regex_actions.hpp> function< op::at >::type const at;