Hi Ryan, On Wed, Aug 11, 2010 at 8:05 PM, Ryan McConnehey <mccorywork@gmail.com> wrote:
I'm trying to create a stream operator for a list of DataPoint objects. I can't get the correct boost::lambda syntax to access what the optional is containing. Could someone tell me what I'm doing wrong?
The problem appears to be that boost::optional<double>::get is overloaded -- there's a const and a non-const version. The most straightforward solution appears to be a cast: #include <boost/optional.hpp> #include <boost/lambda/bind.hpp> #include <boost/lambda/lambda.hpp> #include <iostream> #include <list> struct DataPoint { boost::optional<double> m_Time; }; std::ostream & operator<<(std::ostream & stream, std::list<DataPoint> const& points) { namespace bll = boost::lambda; std::for_each( points.begin(), points.end(), stream << bll::bind(static_cast<double const&(boost::optional<double>::*)() const>(&boost::optional<double>::get), bll::bind(&DataPoint::m_Time, bll::_1)) << " "); return stream; } int main() { DataPoint pt; pt.m_Time = boost::optional<double>(5.); std::list<DataPoint> points(5, pt); std::cout << points << std::endl; return 0; } However, the syntax is opaque. What you suggested in your comment should work and would be nice, but I was also unable to parse the error messages for it. To do what you'd like with Boost.Phoenix (#include <boost/spirit/home/phoenix.hpp> to get all of it) you could replace most of operator<< with the following: namespace bp = boost::phoenix; std::for_each(points.begin(), points.end(), stream << *bp::bind(&DataPoint::m_Time, bp::arg_names::_1) << " "); Much cleaner, if that option's available to you. Good luck, Nate