boost.spirit x3 move_to and list ast member

Question

BNF I實施了一個有趣的規則，根據運營商的不同，這些條款可以是鏈接的或事件不符合此生產規則。因此，我使用同樣的AST數據結構，因爲僅枚舉變化：

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

#include <iostream> 
#include <string> 
#include <list> 


namespace ast 
{ 
    struct identifer { 
     int      name; 
    }; 
    struct expression { 
     struct chunk { 
      char    operator_; 
      ast::identifer  identifer; 
     }; 
     ast::identifer   identifer; 
     std::list<chunk>  chunk_list; 
    }; 
} 

BOOST_FUSION_ADAPT_STRUCT(ast::identifer, 
    name 
) 

BOOST_FUSION_ADAPT_STRUCT(ast::expression::chunk, 
    operator_, identifer 
) 

BOOST_FUSION_ADAPT_STRUCT(ast::expression, 
    identifer, chunk_list 
) 


namespace boost { namespace spirit { namespace x3 { namespace traits { 


void move_to(ast::expression::chunk&& chunk, std::list<ast::expression::chunk>& chunk_list, 
     mpl::identity<container_attribute>) 
{ 
    chunk_list.emplace(chunk_list.end(), std::move(chunk)); 
} 

} } } } 


namespace parser 
{ 
    namespace x3 = boost::spirit::x3; 

    auto const identifier = x3::rule<struct _, int> { "identifier" } = 
     x3::int_; 

    auto const operator_1 = x3::rule<struct _, char> { "operator" } = 
     x3::char_("ABC"); 
    auto const operator_2 = x3::rule<struct _, char> { "operator" } = 
     x3::char_("XYZ"); 

    auto const expression_chunk_1 = x3::rule<struct _, ast::expression::chunk> { "expression" } = 
     operator_1 > identifier 
     ; 
    auto const expression_chunk_2 = x3::rule<struct _, ast::expression::chunk> { "expression" } = 
     operator_2 > identifier 
     ; 
    auto const expression = x3::rule<struct _, ast::expression> { "expression" } = 
      identifier >> *expression_chunk_1 // foo { and foo } 
     // rule below fails to compile 
     | identifier >> expression_chunk_2 // foo [ nand foo ] 
     ; 
} 


struct visitor { 
    visitor(std::ostream& os) : os{ os } { } 
    void operator()(ast::expression const& node) { 
     os << "("; 
     (*this)(node.identifer); 
     for(auto const& chunk : node.chunk_list) { 
      os << "(" << chunk.operator_ << " "; 
      (*this)(chunk.identifer); 
      os << ")"; 
     } 
     os << ")\n"; 
    } 
    void operator()(ast::identifer const& node) { 
     os << "(" << node.name << ")"; 
    } 
    std::ostream& os; 
}; 


int main() 
{ 
    namespace x3 = boost::spirit::x3; 

    for(std::string const str: { 
     "1 X 2", 
     "3 A 4 A 5" 
    }) { 
     auto iter = str.begin(), end = str.end(); 

     ast::expression attr; 
     bool r = x3::phrase_parse(iter, end, parser::expression, x3::space, attr); 

     std::cout << "parse '" << str << "': "; 
     if (r && iter == end) { 
     std::cout << "succeeded:\n"; 
     visitor(std::cout)(attr); 

     } else { 
     std::cout << "*** failed ***\n"; 
     } 
    } 

    return 0; 
} 

這是想法 - 運營商X，Y，Z只增加一個塊列出。編譯器錯誤後，我必須專門化x3 :: traits :: move_to，但我沒有找到任何解決方案來編譯它。什麼是要做的？是列表:: emplace（）和std :: move（）在這裏安全嗎？

Answer 1

我會沒有這個特質。相反，要人爲地使用repeat在vector<T>語法結果：

auto const expression = x3::rule<struct _, ast::expression> { "expression" } = 
     identifier >> *expression_chunk_1 // foo { and foo } 
    | identifier >> x3::repeat(1) [ expression_chunk_2 ] // foo [ nand foo ] 
    ;