在参考了多个教程后(例如 http://boost-spirit.com/home/articles/qi-example/nabialek-trick/),我想使用Nabialek技巧实现动态解析器。解析已经很好的实现了,但是我无法传递属性。像https://dev59.com/4m025IYBdhLWcg3wW0kc#9109972这样的解释表明,属性应该是可能的,但不是参数。
这只是一个将字符串和数字解析到结构体中的小例子。它仅用于展示我的问题;此方法应该在稍后使用真正需要动态解析器的更大系统中使用。
问题:如何使用Nabialek技巧传递属性?
我不是精通spirit的专家,请耐心等待。我使用的是gcc 4.8.1和boost 1.54。
#define BOOST_SPIRIT_DEBUG
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;
//------------------------------------------------------------------------------
// Data structure
struct myline {
myline()
: _n(0), _s("") {
}
myline(int n, std::string s)
: _n(n), _s(s) {
}
void set(int n, std::string s) {
_n = n;
_s = s;
}
int _n;
std::string _s;
};
BOOST_FUSION_ADAPT_STRUCT(::myline, (int, _n) (std::string, _s))
//------------------------------------------------------------------------------
// Parser grammar
template<typename It, typename Skipper = qi::space_type>
struct parser: qi::grammar<It, myline(), Skipper> {
parser()
: parser::base_type(start) {
using namespace qi;
start = line;
string %= qi::lexeme["'" >> *~qi::char_("'") >> "'"];
one = (string >> "@" >> qi::int_)[_val = phx::construct<myline>(_2, _1)];
two = (qi::int_ >> "@" >> string);
keyword.add("one", &one)("two", &two);
line = keyword[_a = _1] >> qi::lazy(*_a);
on_error<fail>(
start,
std::cout << phx::val("Error! Expecting ") << _4
<< phx::val(" here: \"") << phx::construct<std::string>(_3, _2)
<< phx::val("\"\n"));
BOOST_SPIRIT_DEBUG_NODES((start)(line)(one)(two))
}
private:
template<typename Attr> using Rule = qi::rule<It, Attr(), Skipper>;
Rule<myline> start, one, two;
qi::rule<It, myline, Skipper, qi::locals<Rule<myline>*> > line;
Rule<std::string> string;
qi::symbols<char, Rule<myline>*> keyword;
};
//------------------------------------------------------------------------------
int main() {
for (const std::string input : std::vector<std::string> { "one 'test'@1",
"two 2@'test'" }) {
auto f(std::begin(input)), l(std::end(input));
const static parser<decltype(f)> p;
myline parsed_script;
bool ok = qi::phrase_parse(f, l, p, qi::space, parsed_script);
if (!ok) {
std::cout << "invalid input\n";
}
std::cout << parsed_script._n << ": " << parsed_script._s << std::endl;
if (f != l) {
std::cout << "unparsed: '" << std::string(f, l) << "'" << std::endl;
}
}
}
解析结果:
<start>
<try>one 'test'@1</try>
<line>
<try>one 'test'@1</try>
<one>
<try> 'test'@1</try>
<success></success>
<attributes>[[1, [t, e, s, t]]]</attributes>
</one>
<success></success>
<attributes>[]</attributes><locals>(0x43b0e0)</locals>
</line>
<success></success>
<attributes>[[0, []]]</attributes>
</start>
<start>
<try>two 2@'test'</try>
<line>
<try>two 2@'test'</try>
<two>
<try> 2@'test'</try>
<success></success>
<attributes>[[2, [t, e, s, t]]]</attributes>
</two>
<success></success>
<attributes>[]</attributes><locals>(0x43b110)</locals>
</line>
<success></success>
<attributes>[[0, []]]</attributes>
</start>