Boost spirit X3: Unable to create an AST that has a optional list - c++14

Question

I am trying to parse a optional list of things followed by a semicolon (this is a simplified example). Below is a example program:
#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;
}
However it fails to compile with the error:
usr/include/boost/spirit/home/x3/support/ast/variant.hpp:184:17: error: no match for ‘operator=’ (operand types are ‘boost::spirit::x3::variant<double, std::__cxx11::basic_string<char, std::char_traits, std::allocator<cha
r> > >::variant_type’ {aka ‘boost::variant<double, std::__cxx11::basic_string<char, std::char_traits, std::allocator > >’} and ‘std::optionalclient::ast::pass’)
26 184 | var = std::forward(rhs);
What am I doing wrong? The error is not very informative. It seems to work fine if I just do a optional of things.
I am using the following command (the file name is r1.cpp):
g++ --std=c++17 r1.cpp -o r1

Answer 1

With the following MRE(Minimal Reproducible Example):
#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);
I get no compiler errors.
Please provide an MRE showing the error.