boost::spirit reusage of grammar objects

Question

Imagine there is a rule to parse some name:

m_sName = qi::lexeme[
    (ascii::alpha | qi::char_('_')) >> *(ascii::alnum | qi::char_('_'))
]

Could one use the same object for parsing two names in series or does one have to instantiate m_sName1 and m_sName2?

m_sName >> m_sName

Answer 1

I made a sample that might help:

Live On Coliru

#include <boost/spirit/include/qi.hpp>
#include <iomanip>

int main() {
    namespace qi = boost::spirit::qi;
    using It     = std::string::const_iterator;

    qi::rule<It, std::string()> m_sName = (qi::alpha | qi::char_('_')) >> *(qi::alnum | qi::char_('_'));

    for (std::string const input : {"foo bar qux_net"}) {
        std::string a, b, c;
        if (phrase_parse(input.begin(), input.end(), m_sName >> m_sName >> m_sName, qi::space, a, b, c)) {
            std::cout << quoted(a) << " " << quoted(b) << " " << quoted(c) << "\n";
        }
    }
}

Prints

"foo" "bar" "qux_net"

NOTES

• note I removed lexeme because the rule is already skipper-less (see Boost spirit skipper issues)
• Note that I'd probably write the rule as qi::raw[(qi::alpha | '_') >> *(qi::alnum | '_')] which can be more efficient. It works well if your attribute reflects the source sequence unmodified.