c++ - boost::spirit::qi 和 boost::phoenix::push_back

Question

基于 Using boost::spirit::qi and boost::phoenix::push_back 上的 QA ，以下代码运行良好 - 使用 C++14 编译。

#include <string>
#include <vector>
#include <iostream>

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
namespace qi = boost::spirit::qi;

typedef std::vector<unsigned int> uint_vector_t;

std::ostream& operator<<(std::ostream& out, const uint_vector_t &data)
{
    for (unsigned int i(0); i < data.size(); i++)
    {
        out << data[i] << '\n';
    }
    return out;
}

struct MyStruct
{
    uint_vector_t m_aList;
    uint_vector_t m_bList;
};


template<typename Iterator, typename Skipper>
struct MyParser : public boost::spirit::qi::grammar<Iterator,
        MyStruct(),Skipper>
{
    MyParser() :
        MyParser::base_type(Parser, "Parser")
    {
        using boost::spirit::qi::uint_;
        using boost::spirit::qi::_val;
        using boost::spirit::qi::_1;

        using boost::phoenix::at_c;
        using boost::phoenix::push_back;
        using boost::phoenix::bind;

        aParser = "a=" >> uint_;
        bParser = "b=" >> uint_;

        Parser =
           *(  aParser [push_back(bind(&MyStruct::m_aList, _val), _1)]
            |  bParser [push_back(bind(&MyStruct::m_bList, _val), _1)]
            );
    }
    boost::spirit::qi::rule<Iterator, MyStruct(), Skipper> Parser;
    boost::spirit::qi::rule<Iterator, unsigned int(), Skipper> aParser, bParser;
};

int main()
{
    using boost::spirit::qi::phrase_parse;

    std::string input("a=0\nb=7531\na=2\na=3\nb=246\n");
    std::string::const_iterator begin = input.begin();
    std::string::const_iterator end = input.end();
    MyParser<std::string::const_iterator, qi::space_type> parser;

    MyStruct result;
    bool succes = qi::phrase_parse(begin, end, parser,qi::space,result);
    assert(succes);

    std::cout << "===A===\n" <<result.m_aList << "===B===\n" << result.m_bList << std::endl;
    return 0;
}

结果是:

===A===
0
2
3
===B===
7531
246

在结构中添加另一个 qi::symbols 元素，新添加的元素应该被解析为 FRUIT::APPLE (0)，但实际上它是 indeterminate(随机出现)。

#include <string>
#include <vector>
#include <iostream>

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
namespace qi = boost::spirit::qi;

typedef std::vector<unsigned int> uint_vector_t;

std::ostream& operator<<(std::ostream& out, const uint_vector_t &data)
{
    for (unsigned int i(0); i < data.size(); i++)
    {
        out << data[i] << '\n';
    }
    return out;
}

struct MyStruct
{
    enum class  FRUIT
    {
        APPLE,
        BANANA,
        PEAR,
    } fruit;
    uint_vector_t m_aList;
    uint_vector_t m_bList;
};

BOOST_FUSION_ADAPT_STRUCT
(
    MyStruct,
    (MyStruct::FRUIT, fruit)
    (uint_vector_t, m_aList)
    (uint_vector_t, m_bList)
)


template<typename Iterator, typename Skipper>
struct MyParser : public boost::spirit::qi::grammar<Iterator,
        MyStruct(),Skipper>
{
    MyParser() :
        MyParser::base_type(Parser, "Parser")
    {
        using boost::spirit::qi::uint_;
        using boost::spirit::qi::_val;
            using boost::spirit::qi::_1;

        using boost::phoenix::at_c;
        using boost::phoenix::push_back;
        using boost::phoenix::bind;

        fruiter.add
                ("apple",   MyStruct::FRUIT::APPLE)
                ("banana",  MyStruct::FRUIT::BANANA)
                ("pear",    MyStruct::FRUIT::PEAR)
                ;

        aParser = "a=" >> uint_;
        bParser = "b=" >> uint_;

        Parser = fruiter >>
           *(  aParser [push_back(bind(&MyStruct::m_aList, _val), _1)]
            |  bParser [push_back(bind(&MyStruct::m_bList, _val), _1)]
            );
    }
    boost::spirit::qi::rule<Iterator, MyStruct(), Skipper> Parser;
    boost::spirit::qi::rule<Iterator, unsigned int(), Skipper> aParser, bParser;
    boost::spirit::qi::symbols<char, MyStruct::FRUIT>                   fruiter;
};

int main()
{
    using boost::spirit::qi::phrase_parse;

    std::string input("apple\na=0\nb=7531\na=2\na=3\nb=246\n");
    std::string::const_iterator begin = input.begin();
    std::string::const_iterator end = input.end();
    MyParser<std::string::const_iterator, qi::space_type> parser;

    MyStruct result;
    bool succes = qi::phrase_parse(begin, end, parser,qi::space,result);
    assert(succes);

    std::cout << "Fruit: " << int(result.fruit) << "\n===A===\n" <<result.m_aList << "===B===\n" << result.m_bList << std::endl;
    return 0;
}

生成的 qi::symbols 元素是随机的而不是 0。示例输出如下所示

Fruit: 29899839
===A===
0
2
3
===B===
7531
246

然而，qi::symbols 元素本身也只能正常工作。

#include <string>
#include <vector>
#include <iostream>

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
namespace qi = boost::spirit::qi;


struct MyStruct
{
    enum class  FRUIT
    {
        APPLE,
        BANANA,
        PEAR,
    } fruit;
};

BOOST_FUSION_ADAPT_STRUCT
(
    MyStruct,
    (MyStruct::FRUIT, fruit)
)


template<typename Iterator, typename Skipper>
struct MyParser : public boost::spirit::qi::grammar<Iterator,
        MyStruct(),Skipper>
{
    MyParser() :
        MyParser::base_type(Parser, "Parser")
    {
        using boost::spirit::qi::uint_;
        using boost::spirit::qi::_val;
            using boost::spirit::qi::_1;

        using boost::phoenix::at_c;
        using boost::phoenix::push_back;
        using boost::phoenix::bind;

        fruiter.add
                ("apple",   MyStruct::FRUIT::APPLE)
                ("banana",  MyStruct::FRUIT::BANANA)
                ("pear",    MyStruct::FRUIT::PEAR)
                ;

        Parser = fruiter;
    }
    boost::spirit::qi::rule<Iterator, MyStruct(), Skipper> Parser;
    boost::spirit::qi::symbols<char, MyStruct::FRUIT>                   fruiter;
};

int main()
{
    using boost::spirit::qi::phrase_parse;

    std::string input("apple");
    std::string::const_iterator begin = input.begin();
    std::string::const_iterator end = input.end();
    MyParser<std::string::const_iterator, qi::space_type> parser;

    MyStruct result;
    bool succes = qi::phrase_parse(begin, end, parser,qi::space,result);
    assert(succes);

    std::cout << "Fruit: " << int(result.fruit) << "\n";
    return 0;
}

结果如下:

Fruit: 0

我做错了什么？提前致谢。

Answer 1

语义 Action 禁止属性的自动传播。这显然也是程序的第一个版本不需要对 MyResult 结构进行任何修改的原因。

所以要么

1. 坚持语义操作¹(放弃 adapt-struct)

   Live On Coliru

       Parser = fruiter[bind(&MyStruct::fruit, _val) = _1] >> 
           *( aParser [push_back(bind(&MyStruct::m_aList, _val), _1)] 
           |  bParser [push_back(bind(&MyStruct::m_bList, _val), _1)]
           );
   

2. 或者使用operator%=重新启用自动属性传播语义。

   // NOTE c++11+ syntax:
   BOOST_FUSION_ADAPT_STRUCT(MyStruct, fruit, m_aList, m_bList)
   
   Parser %= fruiter >> 
       *( aParser [push_back(bind(&MyStruct::m_aList, _val), _1)] 
       |  bParser [push_back(bind(&MyStruct::m_bList, _val), _1)]
       );
   

   请注意，如果 fruit 不是第一个改编的序列元素，这很容易崩溃。事实上，只调整预期的元素要干净得多:

   BOOST_FUSION_ADAPT_STRUCT(MyStruct, fruit)
   

   更清晰地明确哪些属性需要传播:

   Parser %= fruiter >> 
       omit [
          *( aParser [push_back(bind(&MyStruct::m_aList, _val), _1)] 
           | bParser [push_back(bind(&MyStruct::m_bList, _val), _1)]
           )
       ];
   

   Live On Coliru

完整 list

Live On Coliru

#include <iostream>
#include <string>
#include <vector>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/include/qi.hpp>
namespace qi = boost::spirit::qi;

typedef std::vector<unsigned int> Uints;

namespace std {
    std::ostream& operator<<(std::ostream& out, const Uints &data) {
        for (auto i : data) out << i << " ";
        return out << "\n";
    }
}

struct MyStruct {
    enum class FRUIT {
        APPLE,
        BANANA,
        PEAR,
    } fruit;

    friend std::ostream& operator<<(std::ostream& out, FRUIT f) {
        switch(f) {
            case FRUIT::APPLE:  return out << "APPLE";
            case FRUIT::BANANA: return out << "BANANA";
            case FRUIT::PEAR:   return out << "PEAR";
        }
        return out << "FRUIT[?" << static_cast<int>(f) << "]";
    }
    Uints m_aList;
    Uints m_bList;
};

BOOST_FUSION_ADAPT_STRUCT(MyStruct, fruit)

template <typename Iterator, typename Skipper>
struct MyParser : public qi::grammar<Iterator, MyStruct(), Skipper> {
    MyParser() : MyParser::base_type(Parser, "Parser") {
        using namespace qi;
        using boost::phoenix::push_back;
        using boost::phoenix::bind;

        fruiter.add("apple", MyStruct::FRUIT::APPLE)("banana", MyStruct::FRUIT::BANANA)("pear", MyStruct::FRUIT::PEAR);

        aParser = "a=" >> uint_;
        bParser = "b=" >> uint_;

        Parser %= fruiter >> 
            omit [
               *( aParser [push_back(bind(&MyStruct::m_aList, _val), _1)] 
                | bParser [push_back(bind(&MyStruct::m_bList, _val), _1)]
                )
            ];
    }
  private:
    qi::rule<Iterator, MyStruct(), Skipper> Parser;
    qi::rule<Iterator, unsigned int(), Skipper> aParser, bParser;
    qi::symbols<char, MyStruct::FRUIT> fruiter;
};

int main() {
    std::string input("banana\na=0\nb=7531\na=2\na=3\nb=246\n");
    using It = std::string::const_iterator;
    It begin = input.begin(), end = input.end();
    MyParser<It, qi::space_type> parser;

    MyStruct result;
    bool succes = qi::phrase_parse(begin, end, parser, qi::space, result);

    if (succes) {
        std::cout 
            << "Fruit: " << result.fruit 
            << "\n===A===\n" <<result.m_aList << "===B===\n" << result.m_bList << std::endl;
    } else {
        std::cout << "Parse failed\n";
    }
}

打印

Fruit: BANANA
===A===
0 2 3 
===B===
7531 246 

¹ 重复我的口头禅:Boost Spirit: "Semantic actions are evil"?