struct puzzle

Following Seth's excellent example, the attached simple program parses
an int and a map of strings. The puzzle is why it no longer compiles
when I remove the int with the following patch:

@@ -11,23 +11,21 @@
 using Map = std::map<std::string, std::string>;
 
 struct result {
-    int onemore;
     Map both;
 };
 
-BOOST_FUSION_ADAPT_STRUCT(result, onemore, both)
+BOOST_FUSION_ADAPT_STRUCT(result, both)
 
 int main()
 {
-    std::string const buf("1;one two;three four;");
+    std::string const buf("one two;three four;");
     auto iter = buf.begin(), end = buf.end();
     auto parser = []{
         using namespace boost::spirit::x3;
 
         auto string_ = lexeme[+alpha];
         auto map_    = (string_ >> string_) >> ';';
-	auto num_    = int_ >> ';';
-	auto all_    = num_ >> +map_;
+	auto all_    = +map_;
 
         return rule<struct _, struct result> {"parser"} = skip(space) [ all_ ];
     };
@@ -49,6 +47,5 @@
         for (auto p : res.both) {
             std::cout << "found: " << p.first << ' ' << p.second << std::endl;
         }
-	std::cout << "and: " << res.onemore << " !" << std::endl;
     }
 }


Less is more?

Cheers,

Patrick

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#define BOOST_SPIRIT_X3_DEBUG

#include <map>

#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/std_pair.hpp>
#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/include/as_vector.hpp>
#include <iostream>

using Map = std::map<std::string, std::string>;

struct result {
    int onemore;
    Map both;
};

BOOST_FUSION_ADAPT_STRUCT(result, onemore, both)

int main()
{
    std::string const buf("1;one two;three four;");
    auto iter = buf.begin(), end = buf.end();
    auto parser = []{
        using namespace boost::spirit::x3;

        auto string_ = lexeme[+alpha];
        auto map_    = (string_ >> string_) >> ';';
	auto num_    = int_ >> ';';
	auto all_    = num_ >> +map_;

        return rule<struct _, struct result> {"parser"} = skip(space) [ all_ ];
    };
   
    result res;
    bool ok = parse(iter, end, parser(), res);

    if (ok) {
        std::cout << "Parse success\n";
    }
    else {
        std::cout << "Parsing failed\n";
    }

    if (iter != end) {
        std::cout << "Bit left over at the end: " << std::string(iter, end) << std::endl;
    }
    else {
        for (auto p : res.both) {
            std::cout << "found: " << p.first << ' ' << p.second << std::endl;
        }
	std::cout << "and: " << res.onemore << " !" << std::endl;
    }
}