boost::pfr::less — std::less like comparator that returns boost::pfr::lt (x, y)
// In header: <boost/pfr/functors.hpp> template<typename T> struct less { // public member functions (, ) ; };
less
( x, y) ;
Returns:
true if field of x less than the field with same index of y and all previous fields of x equal to the same fields of y.