[Boost-users] fusion io problem

Subject: [Boost-users] fusion io problem
From: Olaf Peter (ope-devel_at_[hidden])
Date: 2013-05-05 02:03:41

Hello,

I run into the problem to provide ostream operator<< support for 
spirit's debug facility and for lazyness using fusion's io support:

---8<---
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/io.hpp>
#include <iostream>

namespace fusion = boost::fusion;

namespace client {

     struct point {
             int x,y;
     };

     template<typename CharT>
     std::basic_ostream<CharT>& operator<<(std::basic_ostream<CharT>& 
os, point const& p) {
         os << p;
         return os;
     }

     struct arc {
         int radius;
         point begin;
         point end;
     };

     template<typename CharT>
     std::basic_ostream<CharT>& operator<<(std::basic_ostream<CharT>& 
os, arc const& a) {
         os << a;
         return os;
     }
}

BOOST_FUSION_ADAPT_STRUCT(
      client::point,
     (int, x)
     (int, y)
)

BOOST_FUSION_ADAPT_STRUCT(
      client::arc,
     (int, radius)
     (client::point, begin)
     (client::point, end)
)

int main()
{
     client::arc arc;
     std::cout << arc << '\n';
}

--->8---

This program crashs, I would assume operator<<(..., arc) calls infinity 
recursive fusion's operator<< or similar - that's what I would interpret 
from gdb's backtrace.

How to prevent this? I don't like to investigate much effort of 
formatting to supporting spirit's debug support and conventional 
debugging by tracing the selective printed output (like printf 
debugging) since there is support for formatted output of fusion sequences.

Thanks,
Olaf