1

我有一个案例，我想通过 std::map 过滤作为规则内部综合属性出现的值。

  • 地图是预先生成的，在解析过程中不会改变。
  • 映射的性质和真正的解析器意味着查找永远不会失败（尽管元素的实际数量可能非常大）
  • 完全适合这个问题的常用方法（使用符号表）不适合实际情况。在真正的问题中，查找是基于一个属性的条件，该属性直到解析的很晚才会出现（在一个稍微删除的规则中）。

我的尝试：

#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/foreach.hpp>
#include <string>
#include <iostream>
#include <vector>
#include <map>

namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;

int main() {

    std::map<unsigned int, unsigned int> myMap;
    myMap[1] = 100; myMap[2] = 200; myMap[3] = 300;

    std::string test = "1 2 3";
    std::vector<unsigned int> results;

    qi::rule<std::string::iterator, unsigned int()> r
                      = qi::uint_ [qi::_val = phx::at(myMap, qi::_1)];

    qi::parse(test.begin(), test.end(), ( r % " " ), results);

    BOOST_FOREACH(unsigned int &x, results) {
        std::cout << x << "\n";
    }
}

我想我的印象是，由于凤凰对stl 容器的支持，这应该可以工作。但是我在规则行上得到一个编译错误。如果我用经典的无意义的语义动作替换这个错误[qi::_val = qi::_1]（不足为奇），这个错误就会消失。

像往常一样，MSVS10 下的编译器错误非常长，但这是我的代码文件的第一次提及：（在 C:\code\Compiler2\spirit_test.cpp(25)... 第 25 行是规则r）

C:\boost_1_50_0\boost/spirit/home/qi/nonterminal/rule.hpp(191) : see reference to function template instantiatio
n 'void boost::spirit::qi::rule<Iterator,T1>::define<boost::mpl::false_,Expr>(boost::spirit::qi::rule<Iterator,T1> &,con
st Expr &,boost::mpl::true_)' being compiled
        with
        [
            Iterator=std::_String_iterator<char,std::char_traits<char>,std::allocator<char>>,
            T1=unsigned int (void),
            Expr=boost::proto::exprns_::expr<boost::proto::tagns_::tag::subscript,boost::proto::argsns_::list2<const boo
st::spirit::terminal<boost::spirit::tag::uint_> &,const boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::p
roto::tagns_::tag::assign,boost::proto::argsns_::list2<boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal,b
oost::proto::argsns_::term<boost::spirit::attribute<0>>,0>,boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost
::phoenix::detail::tag::function_eval,boost::proto::argsns_::list3<boost::proto::exprns_::basic_expr<boost::proto::tagns
_::tag::terminal,boost::proto::argsns_::term<boost::phoenix::stl::at_impl>,0>,boost::phoenix::actor<boost::proto::exprns
_::basic_expr<boost::proto::tagns_::tag::terminal,boost::proto::argsns_::term<boost::reference_wrapper<std::map<unsigned
 int,unsigned int>>>,0>>,boost::phoenix::actor<boost::spirit::argument<0>>>,3>>>,2>> &>,2>
        ]
        C:\code\Compiler2\spirit_test.cpp(25) : see reference to function template instantiation 'boost::spirit::qi
::rule<Iterator,T1>::rule<boost::proto::exprns_::expr<Tag,Args,Arity>>(const Expr &,const std::string &)' being compiled

        with
        [
            Iterator=std::_String_iterator<char,std::char_traits<char>,std::allocator<char>>,
            T1=unsigned int (void),
            Tag=boost::proto::tagns_::tag::subscript,
            Args=boost::proto::argsns_::list2<const boost::spirit::terminal<boost::spirit::tag::uint_> &,const boost::ph
oenix::actor<boost::proto::exprns_::basic_expr<boost::proto::tagns_::tag::assign,boost::proto::argsns_::list2<boost::pro
to::exprns_::expr<boost::proto::tagns_::tag::terminal,boost::proto::argsns_::term<boost::spirit::attribute<0>>,0>,boost:
:phoenix::actor<boost::proto::exprns_::basic_expr<boost::phoenix::detail::tag::function_eval,boost::proto::argsns_::list
3<boost::proto::exprns_::basic_expr<boost::proto::tagns_::tag::terminal,boost::proto::argsns_::term<boost::phoenix::stl:
:at_impl>,0>,boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::proto::tagns_::tag::terminal,boost::proto::a
rgsns_::term<boost::reference_wrapper<std::map<unsigned int,unsigned int>>>,0>>,boost::phoenix::actor<boost::spirit::arg
ument<0>>>,3>>>,2>> &>,
            Arity=2,
            Expr=boost::proto::exprns_::expr<boost::proto::tagns_::tag::subscript,boost::proto::argsns_::list2<const boo
st::spirit::terminal<boost::spirit::tag::uint_> &,const boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::p
roto::tagns_::tag::assign,boost::proto::argsns_::list2<boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal,b
oost::proto::argsns_::term<boost::spirit::attribute<0>>,0>,boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost
::phoenix::detail::tag::function_eval,boost::proto::argsns_::list3<boost::proto::exprns_::basic_expr<boost::proto::tagns
_::tag::terminal,boost::proto::argsns_::term<boost::phoenix::stl::at_impl>,0>,boost::phoenix::actor<boost::proto::exprns
_::basic_expr<boost::proto::tagns_::tag::terminal,boost::proto::argsns_::term<boost::reference_wrapper<std::map<unsigned
 int,unsigned int>>>,0>>,boost::phoenix::actor<boost::spirit::argument<0>>>,3>>>,2>> &>,2>
        ]
C:\boost_1_50_0\boost/proto/transform/default.hpp(154) : error C2440: '=' : cannot convert from 'std::pair<_Ty1,_Ty2>' t
o 'unsigned int'
        with
        [
            _Ty1=const unsigned int,
            _Ty2=unsigned int
        ]
        No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
4

2 回答 2

3

从评论转发

尝试qi::_val = phx::ref(myMap)[qi::_1]而不是qi::_val = phx::at(myMap, qi::_1)。

于 2013-01-07T22:52:40.960 回答
2

问题是 phoenix::at 的返回类型在此标头中定义为container::value_type. 在地图的情况下这是一对。只需将结果专门化为 map 即可（使用 ildjarn 指出的 ref ）。

#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/foreach.hpp>
#include <string>
#include <iostream>
#include <vector>
#include <map>

namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;

namespace boost { namespace phoenix { namespace stl {
    template <typename This, typename Key, typename Value, typename Compare, typename Allocator, typename Index>
        struct at_impl::result<This(std::map<Key,Value,Compare,Allocator>&, Index)>
        {
            typedef Value & type;
        };
    template <typename This, typename Key, typename Value, typename Compare, typename Allocator, typename Index>
        struct at_impl::result<This(std::map<Key,Value,Compare,Allocator> const&, Index)>
        {
            typedef Value const& type;
        };
}}}

int main() {

    std::map<unsigned int, unsigned int> myMap;
    myMap[1] = 100; myMap[2] = 200; myMap[3] = 300;

    std::string test = "1 2 3";
    std::vector<unsigned int> results;

    qi::rule<std::string::iterator, unsigned int()> r
                      = qi::uint_ [qi::_val = phx::at(phx::cref(myMap), qi::_1)];

    qi::parse(test.begin(), test.end(), ( r % " " ), results);

    BOOST_FOREACH(unsigned int &x, results) {
        std::cout << x << "\n";
    }
}
于 2013-01-08T00:27:03.033 回答