JSON parser with Boost Spirit

json.cpp

#include <boost/any.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/fusion/include/std_pair.hpp> 

#include <vector>
#include <map>
#include <iostream>

namespace json {

namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;

struct nullptr_t_ : qi::symbols< char, void * > {
	nullptr_t_() {
		add( "null", nullptr );
	}
} nullptr_;

template< typename Iterator >
struct Grammar : qi::grammar< Iterator, boost::any(), ascii::space_type > {
	Grammar(): Grammar::base_type( start ) {
		using qi::lexeme;
		using qi::double_;
		using qi::bool_;
		using ascii::char_;

		start = value_rule.alias();
		object_rule = '{' >> pair_rule % ',' >> '}';
		pair_rule = string_rule >> ':' >> value_rule;
		value_rule = object_rule | array_rule | string_rule | nullptr_ | double_ | bool_;
		array_rule = '[' >> value_rule % ',' >> ']';
		string_rule = lexeme[ '\"' >> *( char_ - '\"' ) >> '\"' ];
	}

	qi::rule< Iterator, boost::any(), ascii::space_type > start;
	qi::rule< Iterator, std::map< std::string, boost::any >(), ascii::space_type > object_rule;
	qi::rule< Iterator, std::pair< std::string, boost::any >(), ascii::space_type > pair_rule;
	qi::rule< Iterator, boost::any(), ascii::space_type > value_rule;
	qi::rule< Iterator, std::vector< boost::any >(), ascii::space_type > array_rule;
	qi::rule< Iterator, std::string(), ascii::space_type > string_rule;
};

}

int main() {
	const std::string source = "[ null ]";
	json::Grammar< std::string::const_iterator > g;
	boost::any v;
	auto bit = source.begin();
	auto eit = source.end();
	bool r = boost::spirit::qi::phrase_parse( bit, eit, g, boost::spirit::ascii::space, v );
	if( r ) {
		auto a = boost::any_cast< std::vector< boost::any > >( v );
		for( auto it = a.begin(); it != a.end(); ++it ) {
			std::cout << boost::any_cast< void * >( *it ) << std::endl;
		}
	}
	return 0;
}