I'm trying to output parameters, they can either be a single parameter or a vector of parameters. The following code does not what I'd like it to do:
#include <iostream>
#include <string>
#include <boost/variant.hpp>
#include <boost/spirit/include/karma.hpp>
namespace karma = boost::spirit::karma;
typedef std::vector<int> ParameterList;
typedef boost::variant<int, ParameterList> Parameter;
main()
{
using karma::int_;
using karma::eol;
using karma::lit;
std::string generated;
std::back_insert_iterator<std::string> sink(generated);
karma::rule<std::back_insert_iterator<std::string>, ParameterList()> parameterListRule = int_ % lit(", ");
karma::rule<std::back_insert_iterator<std::string>, Parameter()> parameterRule = (int_ | parameterListRule) << eol;
karma::generate(sink, parameterRule, 1); // Works
karma::generate(sink, parameterRule, ParameterList{1, 2}); // Doesn't work
std::cout << generated << "\n";
}
(The real code has other types of parameters, not just int, and I cannot just make everything a ParameterList.)
I do not quite understand how to make this work, in particular since an analogous construction for parsing works fine for me using boost::spirit::qi.
In your second call you didn't put a variant in the generator, but the rule expects one.
#include <iostream>
#include <string>
#include <boost/variant.hpp>
#include <boost/spirit/include/karma.hpp>
namespace karma = boost::spirit::karma;
typedef std::vector<int> ParameterList;
typedef boost::variant<int, ParameterList> Parameter;
main()
{
using karma::int_;
using karma::eol;
using karma::lit;
std::string generated;
std::back_insert_iterator<std::string> sink(generated);
karma::rule<std::back_insert_iterator<std::string>, ParameterList()> parameterListRule = int_ % lit(", ");
karma::rule<std::back_insert_iterator<std::string>, Parameter()> parameterRule = (int_ | parameterListRule) << eol;
karma::generate(sink, parameterRule, 1); // Works
// use variant here:
Parameter test(ParameterList{1, 2});
karma::generate(sink, parameterRule, test);
std::cout << generated << "\n";
}