c++ - Xpressive >>= Operator -

i toying around boost xpressive , having trouble following snippet

#include <iostream> #include <string> #include <boost/xpressive/xpressive.hpp>  using namespace std; using namespace boost::xpressive;  int main() {     string s("123");     sregex rex = _d;     rex >>= _d;      smatch what;      regex_search(s, what, rex);      cout << "match: " << what[0] << endl;      return 0;  } 

the result of running program match of 1 opposed expected 12. sregex::operator>>= have different meaning/use intuitively assumed? expecting yield sregex similar _d >> _d.

xpressive doesn't support >>= operator. fact code compiles @ considered bug. try:

rex = rex >> _d; 

however, building regex piecemeal make regex perform poorly.