Parsing list of variants with boost spirit X3

Question

I try to parse a simple list of float or int into a vector of variant. I'm using boost 1.64 on Windows (mingw 64bit).

Here is a minimal example:

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

#include <iostream>
#include <vector>

namespace x3 = boost::spirit::x3;

struct var : x3::variant<int, float> {
    using base_type::base_type;
    using base_type::operator=;
};

struct block {
    bool dummy; // needed to make newer boost version compile
    std::vector<var> vars;
};

BOOST_FUSION_ADAPT_STRUCT(block,
    (bool, dummy),
    (std::vector<var>, vars)
);

x3::rule<class var,   var>     const r_var   = "var";
x3::rule<class block, block>   const r_block = "block";

auto const r_var_def   = x3::float_ | x3::int_;
auto const r_block_def = x3::attr(true) >> *x3::lit(";") >> *(r_var >> -x3::lit(","));

BOOST_SPIRIT_DEFINE(r_var, r_block);

bool parse(std::string const &txt, block &ast)
{
    using boost::spirit::x3::phrase_parse;
    using boost::spirit::x3::space;

    auto iter = txt.begin();
    auto end = txt.end();

    const bool parsed = phrase_parse(iter, end, r_block, space, ast);
    return parsed && iter == end;
}

int main() {
    std::vector<std::string> list = {
        "1, 3, 5.5",
        ";1.0, 2.0, 3.0, 4.0"
    };

    for (const auto&i : list) {
        block ast;
        if (parse(i, ast)) {
            std::cout << "OK: " << i << std::endl;
        } else {
            std::cout << "FAIL: " << i << std::endl;
        }
    }
}

GCC 7.1 gives the following error:

..\parser\parser.cpp:41:68:   required from here
..\..\win64\include/boost/spirit/home/x3/nonterminal/detai/rule.hpp:313:24: error: use of deleted function 'var::var(const var&)'
             value_type made_attr = make_attribute::call(attr);
                        ^~~~~~~~~

Any ideas, why GCC doesn't compile it? It works with Clang though.

Live on Coliru (switch to clang++ to see it work).

Answer 1

It seems that there is a problem using the inherited special members. Two workarounds:

using var = x3::variant<int, float>;

Alternatively:

struct var : x3::variant<int, float> {
    var            (          ) = default;
    var            (var const&) = default;
    var& operator= (var const&) = default;
    using base_type::base_type;
    using base_type::operator=;
};