boost::spirit::karma semantic action assignment error

Question

I'm trying to set karmas generator-value by a semantic action, however, it won't compile. I can't find the reson why, as I'm quite sure I use it as explained in the documentation. As I'm new to karma it's most likely I did some rookie mistake. A minimal example:

#include <boost/spirit/include/karma.hpp>
#include <boost/spirit/include/karma_int.hpp>
#include <boost/spirit/include/karma_generate.hpp>

namespace karma = boost::spirit::karma;
int main() {
    std::string s;
    std::back_insert_iterator<std::string> out(s);
    boost::spirit::karma::generate(out,karma::int_[karma::_1=2]); //won't compile
    //boost::spirit::karma::generate(out,karma::int_,2); this compiles and works
    std::cout<<s;
}

results in the comipler error:

 error: no viable overloaded '='

I'm using g++ 4.6.3 and boost 1.48.

Answer 1

You are missing some headers to include. You can either use:

#include <boost/spirit/include/phoenix_operator.hpp> 

that includes the operators needed for this to work, or:

#include <boost/spirit/include/phoenix.hpp>

that includes everything about Boost.Phoenix. On LWS.