I am using a karma genarator thats consuming a vector of pairs - simular to http://boost-spirit.com/home/articles/karma-examples/output-generation-from-a-list-of-key-value-pairs-using-spirit-karma/
i built an example to show my problem following the article above
#include <boost/fusion/include/std_pair.hpp>
#include <boost/spirit/include/karma.hpp>
namespace karma = boost::spirit::karma;
typedef std::pair<std::string, std::string > pair_type;
template <typename OutputIterator>
struct keys_and_values : karma::grammar<OutputIterator, std::vector<pair_type>()>
{
keys_and_values() : keys_and_values::base_type(query)
{
query = *pair;
// here is the interesting part
pair = karma::string << ' ' << karma::string << ' ' << karma::string << karma::eol;
}
karma::rule<OutputIterator, std::vector<pair_type>()> query;
karma::rule<OutputIterator, pair_type()> pair;
};
int main(int argc, char *argv[])
{
typedef std::back_insert_iterator<std::string> sink_type;
std::vector<pair_type> v;
v.push_back(pair_type("key1", "value1"));
v.push_back(pair_type("key2", "value2"));
v.push_back(pair_type("key3", "value3"));
std::string generated;
sink_type sink(generated);
keys_and_values<sink_type> g;
bool result = karma::generate(sink, g, v);
std::cout << generated << std::endl;
return 0;
}
What i am trying to achieve is an output like "value1 key1 value1". Normally it would output "key1 value1" (but only if you delete the third karma::string in my example) i already tried lots of stuff with semantic actions e.g.
pair = karma::string[karma::_1 = karma::_val] ...
However, that doesnt work. I probably need something else to get the value from my std::pair.
These 2 questions looked interesting but didnt solve my problem reuse parsed variable with boost karma How to access data of nested objects in boost::spirit::karma?
Although technically karma::duplicate[]
would seem the natural match here, I'd probably resort to using a local here:
Update: As the commenter noted, I misread and swapped key/value. Here, BOOT_FUSION_ADAPT_STRUCT_NAMED would appear to be in order!
BOOST_FUSION_ADAPT_STRUCT_NAMED(
pair_type const, pair_as_vkv,
(std::string, second)
(std::string, first)
(std::string, second)
)
And, now you can just write
template <typename OutputIterator>
struct keys_and_values : karma::grammar<OutputIterator, std::vector<pair_type>()>
{
keys_and_values() : keys_and_values::base_type(query)
{
query = *pair;
pair = karma::string << ' ' << karma::string << ' ' << karma::string << karma::eol;
}
karma::rule<OutputIterator, std::vector<pair_type>()> query;
karma::rule<OutputIterator, boost::fusion::adapted::pair_as_vkv()> pair;
};
Without further ado: see it Live On Coliru
Output
value1 key1 value1
value2 key2 value2
value3 key3 value3
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/karma.hpp>
typedef std::pair<std::string, std::string> pair_type;
BOOST_FUSION_ADAPT_STRUCT_NAMED(
pair_type const, pair_as_vkv,
(std::string, second)
(std::string, first)
(std::string, second)
)
namespace karma = boost::spirit::karma;
namespace phx = boost::phoenix;
template <typename OutputIterator>
struct keys_and_values : karma::grammar<OutputIterator, std::vector<pair_type>()>
{
keys_and_values() : keys_and_values::base_type(query)
{
query = *pair;
pair = karma::string << ' ' << karma::string << ' ' << karma::string << karma::eol;
}
karma::rule<OutputIterator, std::vector<pair_type>()> query;
karma::rule<OutputIterator, boost::fusion::adapted::pair_as_vkv()> pair;
};
int main(int argc, char *argv[])
{
typedef std::back_insert_iterator<std::string> sink_type;
std::vector<pair_type> v;
v.push_back(pair_type("key1", "value1"));
v.push_back(pair_type("key2", "value2"));
v.push_back(pair_type("key3", "value3"));
std::string generated;
sink_type sink(generated);
keys_and_values<sink_type> g;
karma::generate(sink, g, v);
std::cout << generated << std::endl;
return 0;
}