Re: [Boost-users] [tr1|fusion]at_c<N>() tuple copying problem

From: Joel de Guzman (joel_at_[hidden])
Date: 2008-08-29 10:50:52

Markus Werle wrote:
> Hi!
> 
> The following piece of code yields "( 0)" as output, but IMHO
> the output should be "(test 1)".
> Looks like at_c creates temporaries, but I expected it to
> return a reference. 
> How can I fix this?
> 
> Markus
> 
> #include <boost/spirit/include/phoenix_core.hpp>
> #include <boost/spirit/include/phoenix_fusion.hpp>
> #include <boost/tr1/tuple.hpp>
> #include <string>
> #include <iostream>
> 
> namespace fusion = boost::fusion;
> namespace phoenix = boost::phoenix;
> 
> int main()
> {
> 	typedef fusion::tuple<std::string, int> tuple_t;
> 	typedef std::tr1::tuple<std::string, int> tr1_tuple_t;
> 
> 	tuple_t t("test", 1);
> 	
> 	tr1_tuple_t tr1_t;
> 
> 	phoenix::at_c<0>(tr1_t) = phoenix::at_c<0>(t);
> 	phoenix::at_c<1>(tr1_t) = phoenix::at_c<1>(t);
> 	
> 	
> 	std::cout << tr1_t << std::endl;
> }

I don't understand the code. What is phoenix doing there?
You know phoenix::at_c is lazy, right? Did you mean fusion::at_c?

Regards,
-- 
Joel de Guzman
http://www.boostpro.com
http://spirit.sf.net