[Boost-users] [lambda][optional] Accessing an optional variable through lambda

Subject: [Boost-users] [lambda][optional] Accessing an optional variable through lambda
From: Ryan McConnehey (mccorywork_at_[hidden])
Date: 2010-08-11 22:05:30

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?

Ryan

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(&boost::optional<double>::get, 
bll::bind(&DataPoint::m_Time, bll::_1)) << bll::constant(" "));

    //Would prefer to do something like this 
"*bll::bind(&DataPoint::m_Time, bll::_1)".  This gives me quite the compile
    //error.  Is there a way to use indirection or do I need to bind to 
a optional method to get access?

  return stream;
}