I'm trying to create a parser using boost::spirit::x3 and stumbled upon a strange issue. Despite that this particular use case is presented in the "Using X3" document by Joel de Guzman and Michael Caisse (https://ciere.com/cppnow15/), not all advertised features seem to work.
The problem is that Spirit X3 apparently has trouble synthesizing tuple attribute like std::pair. So, the following construction claimed to produce an attribute with type of pair of strings:
auto item = rule<class item, std::pair<std::string, std::string>>()
= name >> ’:’ >> ( quote | name );
Trivial example:
#include <iostream>
#include <vector>
#include <boost/spirit/home/x3.hpp>
using namespace std;
namespace x3 = boost::spirit::x3;
using x3::int_;
int main()
{
string input = "foo: 146 \n"
"the_answer: 42 \n"
"freeze_point: 0 \n";
cout << input << endl << endl;
auto identifier = x3::rule<class identifier, string>()
= x3::lexeme[(x3::alpha | '_') >> *(x3::alnum | '_')];
auto key_value_pair = x3::rule<class key_value_pair, pair<string, int>>()
= identifier >> ':' >> int_;
auto first = input.begin();
auto last = input.end();
vector<pair<string, int>> output;
bool result = x3::phrase_parse(first, last, *(key_value_pair), x3::space, output);
cout << endl << "Result:" << result << endl << (first - input.begin()) << " of " << (last - input.begin());
return 0;
}
Live on coliru: http://coliru.stacked-crooked.com/a/8980ba6215ae0ce7
This code fails to compile, compiler complains about trying to assign an int to a pair. Why does Spirit do that instead of extracting two values (string and int, respectively) and putting them to a pair? Not sure if it is a bug in boost::spirit::x3, perhaps I am doing something wrong.
Compilers tried: apple-clang, GCC, MSVC17. Boost version is 1.66 or 1.69.
