boost::phoenix try_catch_all 构造编译失败

Question

我正在为日期解析写一个 boost::spirit::qi 语法。

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/date_time.hpp>

template < typename InputIterator >
struct date_rfc1123_grammar :
            boost::spirit::qi::grammar< InputIterator, boost::gregorian::date()> {
    typedef boost::gregorian::date value_type;
    date_rfc1123_grammar() : date_rfc1123_grammar::base_type(date)
    {
        namespace qi = boost::spirit::qi;
        namespace phx = boost::phoenix;
        using qi::_pass;
        using qi::_val;
        using qi::_2;
        using qi::_3;
        using qi::_4;

        _2digits = qi::uint_parser< std::uint32_t, 10, 2, 2 >();
        _4digits = qi::uint_parser< std::uint32_t, 10, 4, 4 >();
        date = (weekday >> ' ' >> _2digits >> ' ' >> month >> ' ' >> _4digits)
            [
              phx::try_[
                _val = phx::construct< value_type >( _4, _3, _2 )
              ].catch_all[
                _pass = false
              ]
            ];
    }
    boost::spirit::qi::rule< InputIterator, value_type()> date;
    weekday_grammar weekday;
    month_grammar month;
    boost::spirit::qi::rule< InputIterator, std::int32_t() > _2digits;
    boost::spirit::qi::rule< InputIterator, std::int32_t() > _4digits;
};

我依靠boost::gregorian::date 构造函数来检查参数，并希望解析器在出现异常时失败。但是boost::phoenix::try_[ ].catch_all[ ] 构造无法编译并显示以下消息：

/path_to_file/datetime_parse.hpp:102:8:   required from ‘tip::http::grammar::parse::date_rfc1123_grammar<InputIterator>::date_rfc1123_grammar() [with InputIterator = boost::spirit::multi_pass<std::istreambuf_iterator<char, std::char_traits<char> > >]’
/path_to_file/grammar_parse_test.hpp:17:7:   required from here
/usr/local/include/boost/proto/traits.hpp:341:13: error: static assertion failed: 0 == Expr::proto_arity_c
             BOOST_STATIC_ASSERT(0 == Expr::proto_arity_c);
             ^

如果没有 try_.catch_all 构造，语法可以编译，但我希望解析器捕获异常并将 _pass 标志设置为 false 以使语法失败。

操作系统和编译器信息：

$ uname -a
Linux zmij 3.19.0-27-generic #29-Ubuntu SMP Fri Aug 14 21:43:37 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
$ g++ -v
Thread model: posix
gcc version 4.9.2 (Ubuntu 4.9.2-10ubuntu13)

提升版本 1.58

Answer 1

我以前见过这个，可能是某些 boost/compiler 版本的本地。

一种解决方法是包含一个无操作语句（例如_pass=_pass），使其成为一个序列：

    date = (weekday >> ' ' >> _2digits >> ' ' >> month >> ' ' >> _4digits)
        [
          _pass = _pass,
          phx::try_[
            _val = phx::construct< value_type >( _4, _3, _2 )
          ].catch_all[
            _pass = false
          ]
        ];

看Live On Coliru

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/date_time/gregorian/greg_date.hpp>

template <typename InputIterator>
struct date_rfc1123_grammar : boost::spirit::qi::grammar< InputIterator, boost::gregorian::date()> 
{
    typedef boost::gregorian::date value_type;
    date_rfc1123_grammar() : date_rfc1123_grammar::base_type(date)
    {
        namespace qi  = boost::spirit::qi;
        namespace phx = boost::phoenix;
        using qi::_pass;
        using qi::_val;
        using qi::_2;
        using qi::_3;
        using qi::_4;

        date = (weekday >> ' ' >> _2digits >> ' ' >> month >> ' ' >> _4digits)
            [
              _pass = _pass,
              phx::try_[
                _val = phx::construct< value_type >( _4, _3, _2 )
              ].catch_all[
                _pass = false
              ]
            ];
    }
    boost::spirit::qi::rule< InputIterator, value_type()> date;
    boost::spirit::qi::rule< InputIterator, uint()> weekday, month;
    boost::spirit::qi::uint_parser< std::uint32_t, 10, 2, 2 > _2digits;
    boost::spirit::qi::uint_parser< std::uint32_t, 10, 4, 4 > _4digits;
};

int main() {
    using It = std::string::const_iterator;
    std::string const input;

    date_rfc1123_grammar<It> g;

    It f = input.begin(), l = input.end();

    boost::gregorian::date d;
    bool ok = boost::spirit::qi::parse(f, l, g, d);

    return ok?1:2;
}