Spirit X3 composed attributes - c++

Question

I am trying to compose spirit rules but I cannot figure out what the attribute of this new rule would be.
The following code is working as I would expect it.
#include <iostream>
#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/io.hpp>
#include <boost/fusion/tuple.hpp>
namespace ast{
struct Record{
int id;
std::string name;
};
struct Document{
Record rec;
Record rec2;
//std::vector<Record> rec;
std::string name;
};
using boost::fusion::operator<<;
}
BOOST_FUSION_ADAPT_STRUCT(ast::Record,
name, id
)
BOOST_FUSION_ADAPT_STRUCT(ast::Document,
rec, rec2,
//rec,
name
)
namespace parser{
namespace x3 = boost::spirit::x3;
namespace ascii = boost::spirit::x3::ascii;
using x3::lit;
using x3::int_;
using ascii::char_;
const auto identifier = +char_("a-z");
const x3::rule<class record, ast::Record> record = "record";
const auto record_def = lit("record") >> identifier >> lit("{") >> int_ >> lit("}");
const x3::rule<class document, ast::Document> document = "document";
const auto document_def =
record >> record
//+record // This should generate a sequence
>> identifier
;
BOOST_SPIRIT_DEFINE(document, record);
}
namespace{
constexpr char g_input[] = R"input(
record foo{42}
record bar{73}
foobar
)input";
}
int main(){
using boost::spirit::x3::ascii::space;
std::string str = g_input;
ast::Document unit;
bool r = phrase_parse(str.begin(), str.end(), parser::document, space, unit);
std::cout << "Got: " << unit << "\n";
return 0;
}
But when I change the rule to parse multiple records(instead of exactly 2) I would expect it to have a std::vector<Record> as an attribute. But all I get is a long compiler error that does not help me very much.
Can someone point me to what I am doing wrong in order to compose the attributes correctly?

Answer 1

I think the whole reason it didn't compile is because you tried to print the result... and std::vector<Record> doesn't know how to be streamed:
namespace ast {
using boost::fusion::operator<<;
static inline std::ostream& operator<<(std::ostream& os, std::vector<Record> const& rs) {
os << "{ ";
for (auto& r : rs) os << r << " ";
return os << "}";
}
}
Some more notes:
adding lexemes where absolutely required (!)
simplifying (no need to BOOST_SPIRIT_DEFINE unless recursive rules/separate TUs)
dropping redundant lit
I arrived at
Live On Coliru
#include <iostream>
#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/io.hpp>
namespace ast {
struct Record{
int id;
std::string name;
};
struct Document{
std::vector<Record> rec;
std::string name;
};
}
BOOST_FUSION_ADAPT_STRUCT(ast::Record, name, id)
BOOST_FUSION_ADAPT_STRUCT(ast::Document, rec, name)
namespace ast {
using boost::fusion::operator<<;
static inline std::ostream& operator<<(std::ostream& os, std::vector<Record> const& rs) {
os << "{ ";
for (auto& r : rs) os << r << " ";
return os << "}";
}
}
namespace parser {
namespace x3 = boost::spirit::x3;
namespace ascii = x3::ascii;
const auto identifier = x3::lexeme[+x3::char_("a-z")];
const auto record = x3::rule<class record, ast::Record> {"record"}
= x3::lexeme["record"] >> identifier >> "{" >> x3::int_ >> "}";
const auto document = x3::rule<class document, ast::Document> {"document"}
= +record
>> identifier
;
}
int main(){
std::string const str = "record foo{42} record bar{73} foobar";
auto f = str.begin(), l = str.end();
ast::Document unit;
if (phrase_parse(f, l, parser::document, parser::ascii::space, unit)) {
std::cout << "Got: " << unit << "\n";
} else {
std::cout << "Parse failed\n";
}
if (f != l) {
std::cout << "Remaining unparsed input: '" << std::string(f,l) << "'\n";
}
}
Prints
Got: ({ (foo 42) (bar 73) } foobar)