boost - 从替代解析器表达式的可变参数列表生成 Spirit 解析器表达式

Question

我正在寻找实现可变参数函数的最简单方法，该函数采用 boost::spirit::qi 规则列表并将列表扩展为格式表达式: rule1 |规则 2 | rule3 |.... 让我们假设规则不合成任何属性。非常感谢您的帮助。

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <string>
#include <iostream>
#include <boost/spirit/include/phoenix_operator.hpp>

namespace qi    = boost::spirit::qi;
namespace ph    = boost::phoenix;
namespace ascii = boost::spirit::ascii;
using boost::spirit::qi::phrase_parse;
using boost::spirit::qi::ascii::space;
using boost::spirit::iso8859_1::char_;

typedef qi::rule<std::string::const_iterator,ascii::space_type> mrule_t;
typedef qi::rule< std::string::const_iterator,std::string() >   wrule_t;

//How to deduce expandBitwise() return type ?

template<typename T>
T expandBitwise(T& t)
{
    return t.rule_;
}

template<typename T,typename ...Tail>
T expandBitwise(T& t,Tail& ...tail)
{
    return t.rule_ | expandBitwise(tail...);
}

struct TStruct
{
    mrule_t     rule_;
    template<typename T,typename R>
    TStruct( T& rVar,const std::string&name, R& rule ) :
        rule_( qi::lit( name ) >> rule[ ph::ref( rVar )=qi::_1 ] )
        {}
};

template<typename T,typename ...Tail>
void mparse(const std::string& line,T& t,Tail& ...tail)
{
    std::string::const_iterator f,l;

    f=line.begin();
    l=line.end();

    // I would like to expand the rules here ...
    //if(phrase_parse(f,l,expandBitwise(t,tail...),space ) && f==l)

    if( phrase_parse(f, l, t.rule_, space ) && f==l )
        std::cout<<"Parsed:"<<line<<std::endl;
    else
        std::cout<<"Syntax error:"<<line<<std::endl;
}

int main()
{
    wrule_t rword=+~space;

    std::string par1,par2,par3,par4;

    TStruct r1( par1,"-a", rword );
    TStruct r2( par2,"-b", rword );
    TStruct r3( par3,"-c", rword );
    TStruct r4( par4,"-d", rword );

    mparse("abc 8.81"   ,r1,r2,r3,r4);
    mparse("-a atoken"  ,r1,r2,r3,r4);
    mparse("-b btoken"  ,r1,r2,r3,r4);
    mparse("-c ctoken"  ,r1,r2,r3,r4);
    mparse("-d dtoken"  ,r1,r2,r3,r4);

    return 0;
}

Answer 1

Thank you for a quick hint! I've just tried your code and unless I do something wrong ... I get this output: Syntax error:abc 8.81 Parsed:-a atoken Syntax error:-b btoken Syntax error:-c ctoken Syntax error:-d dtoken – G. Civardi 2 hours ago

好的，所以，我不能放过它:/

原来是 未定义行为 涉及，因为解析器表达式传递给 expandBitwise 的方式并被复制:Boost Proto 表达式模板不是为了复制而设计的，因为它们可能包含对临时对象的引用，其生命周期在包含完整表达式的末尾结束。

See for more background, the discussion at Zero to 60 MPH in 2 seconds!

经过长时间的调整 rule_.alias()和 boost::proto::deepcopy我已经达到了以下解决方案(顺便说一下，它根本不需要辅助函数了):

template<typename ...Tail>
void mparse(const std::string& line,Tail& ...tail)
{
    auto parser = boost::fusion::fold(
                boost::tie(ph::bind(&TStruct::rule_, arg1)(tail)...),
                qi::eps(false),
                deepcopy_(arg2 | arg1)
            );

    auto f=begin(line), l=end(line);

    if( qi::phrase_parse(f, l, parser, ascii::space ) )
        std::cout << "Parsed:" << line << std::endl;
    else
        std::cout << "Syntax error:" << line << std::endl;

    if (f!=l)
        std::cout << "Remaining unparsed: '" << std::string(f,l) << "'\n";
}

对 UB 的保护是 deepcopy_()调用，这是 boost::proto::deepcopy 的一个简单的多态可调用适配器:

struct DeepCopy
{
    template<typename E> struct result { typedef typename boost::proto::result_of::deep_copy<E>::type type; };

    template<typename E>
        typename result<E>::type
        operator()(E const& expr) const {
            return boost::proto::deep_copy(expr);
        }
};

static const ph::function<DeepCopy> deepcopy_;

使用此代码，瞧，输出变为:

Syntax error:abc 8.81
Remaining unparsed: 'abc 8.81'
Parsed:-a atoken
Parsed:-b btoken
Parsed:-c ctoken
Parsed:-d dtoken
Bye

作为奖励，该代码现在允许您使用 Spirit 的内置 debug() 功能(取消注释该行):

<-d>
  <try>abc 8.81</try>
  <fail/>
</-d>
<-c>
  <try>abc 8.81</try>
  <fail/>
</-c>
<-b>
  <try>abc 8.81</try>
  <fail/>
</-b>
<-a>
  <try>abc 8.81</try>
  <fail/>
</-a>
Syntax error:abc 8.81
Remaining unparsed: 'abc 8.81'

Tested with

• Boost 1_54_0
• GCC 4.7.2, 4.8.x, Clang 3.2
• Note the #defines which are significant.

完整代码

#define BOOST_RESULT_OF_USE_DECLTYPE
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/fusion/adapted/boost_tuple.hpp>
#include <boost/fusion/include/fold.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>

namespace qi    = boost::spirit::qi;
namespace ph    = boost::phoenix;
namespace ascii = boost::spirit::ascii;
using namespace ph::arg_names;

typedef qi::rule<std::string::const_iterator,ascii::space_type> mrule_t;
typedef qi::rule<std::string::const_iterator,std::string() >    wrule_t;

struct TStruct
{
    mrule_t     rule_;
    template<typename T,typename R>
    TStruct( T& rVar,const std::string&name, R& rule ) :
        rule_( qi::lit(name) >> rule[ ph::ref(rVar) = qi::_1 ] )
    { 
        rule_.name(name);
        // debug(rule_);
    }
};

struct DeepCopy
{
    template<typename E> struct result { typedef typename boost::proto::result_of::deep_copy<E>::type type; };

    template<typename E>
        typename result<E>::type
        operator()(E const& expr) const {
            return boost::proto::deep_copy(expr);
        }
};

static const ph::function<DeepCopy> deepcopy_;

template<typename ...Tail>
void mparse(const std::string& line,Tail& ...tail)
{
    auto parser = boost::fusion::fold(
                boost::tie(ph::bind(&TStruct::rule_, arg1)(tail)...),
                qi::eps(false),
                deepcopy_(arg2 | arg1)
            );

    auto f=begin(line), l=end(line);

    if( qi::phrase_parse(f, l, parser, ascii::space ) )
        std::cout << "Parsed:" << line << std::endl;
    else
        std::cout << "Syntax error:" << line << std::endl;

    if (f!=l)
        std::cout << "Remaining unparsed: '" << std::string(f,l) << "'\n";
}

int main()
{
    wrule_t rword=+~ascii::space;

    std::string par1,par2,par3,par4;

    TStruct r1( par1, "-a", rword );
    TStruct r2( par2, "-b", rword );
    TStruct r3( par3, "-c", rword );
    TStruct r4( par4, "-d", rword );

    mparse("abc 8.81"   ,r1,r2,r3,r4);
    mparse("-a atoken"  ,r1,r2,r3,r4);
    mparse("-b btoken"  ,r1,r2,r3,r4);
    mparse("-c ctoken"  ,r1,r2,r3,r4);
    mparse("-d dtoken"  ,r1,r2,r3,r4);

    std::cout << "Bye\n";
}