促进精神X3:无法创建具有可选列表的AST

Question

我试图解析一个可选的事物列表，后面跟着一个分号(这是一个简化的例子)。下面是一个示例程序：

#include <boost/fusion/adapted/struct/adapt_struct.hpp>
#include <boost/fusion/include/io.hpp>
#include <boost/spirit/home/x3.hpp>
#include <boost/spirit/home/x3/support/ast/variant.hpp>
#include <iostream>
#include <optional>
#include <string>
#include <vector>

namespace x3=boost::spirit::x3;

namespace ast
{
  struct doubleOrString : x3::variant<double,std::string>{
     using base_type::base_type;
     using base_type::operator=;
  };
 
  struct pass {
     std::vector<doubleOrString> dOrs;
  };
}//ast namespace

BOOST_FUSION_ADAPT_STRUCT(ast::pass,dOrs)

x3::rule<class doubleOrString_class, ast::doubleOrString> const doubleOrString = "doubleOrString";
x3::rule<class pass_class, ast::pass> const pass = "pass";
x3::rule<class es_class, std::optional<ast::pass>> const es = "es";

auto const doubleOrString_def =x3::double_ | x3::string("AString");
auto const pass_def = doubleOrString % x3::lit(",");
auto const es_def = (pass > x3::lit(";")) | x3::lit(";");

BOOST_SPIRIT_DEFINE(doubleOrString,pass,es);

int main()
{
    using boost::spirit::x3::ascii::space;
    typedef std::string::const_iterator iterator_type;

    std::string str;
    while (getline(std::cin, str))
    {
        if (str.empty() || str[0] == 'q' || str[0] == 'Q')
            break;

        std::optional<ast::pass> esdOrs;
        iterator_type iter = str.begin();
        iterator_type const end = str.end();
        bool r = phrase_parse(iter, end, es, space, esdOrs);
        

        if (r && iter == end)
        {
            std::cout << "\nGood!\n";
        }
        else
        {
            std::cout << "-------------------------\n";
            std::cout << "Parsing failed\n";
            std::cout << "-------------------------\n";
        }
    }

    std::cout << "Bye... :-) \n\n";
    return 0;
}

但是，它无法使用错误进行编译：

usr/include/boost/spirit/home/x3/support/ast/variant.hpp:184:17:错误:不匹配“operator=”(操作数类型为“boost：：spirit：：x3：：variant

r> >>：：variant_type‘{aka’boost：：variant}和‘std：：optionalclient：：ast：：pass’)

26 184 var = std::forward(rhs)；

我做错了什么？这个错误信息不多。如果我只是做一些可选的事情，它似乎会很好。

我使用以下命令(文件名为r1.cpp)：

g++ --std=c++17 r1.cpp -o r1 

Answer 1

使用以下MRE(最小可重现性示例)：

#include <vector>

#include <boost/fusion/adapted/struct/adapt_struct.hpp>
#include <boost/spirit/home/x3.hpp>
#include <boost/spirit/home/x3/support/ast/variant.hpp>

namespace x3=boost::spirit::x3;

namespace ast
{
  struct doubleOrString : x3::variant<double,std::string>{
     using base_type::base_type;
     using base_type::operator=;
  };
 
  struct pass {
     std::vector<doubleOrString> dOrs;
  };
}//ast namespace

BOOST_FUSION_ADAPT_STRUCT(ast::pass,dOrs)

x3::rule<class doubleOrString_class, ast::doubleOrString> const doubleOrString = "doubleOrString";
x3::rule<class pass_class, ast::pass> const pass = "pass";
x3::rule<class es_class, std::optional<ast::pass>> const es = "es";

auto const doubleOrString_def =x3::double_ | x3::string("AString");
auto const pass_def = doubleOrString % x3::lit(",");
auto const es_def = (pass > x3::lit(";")) | x3::lit(";");

BOOST_SPIRIT_DEFINE(doubleOrString,pass,es);

我没有编译器错误。请提供显示错误的MRE。