Hi Ryan,
On Wed, Aug 11, 2010 at 8:05 PM, Ryan McConnehey 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
#include
#include
#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(&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 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
