[Boost-users] Boost.lambda: how to sort this vector with function?

Subject: [Boost-users] Boost.lambda: how to sort this vector with function?
From: Joost Kraaijeveld (J.Kraaijeveld_at_[hidden])
Date: 2009-02-08 17:17:23

I want to sort a vector of Edges according to their remaining estimated
distance to the finish point (an own implementation of a graph
algorithm).

How do I sort this vector with edges:

// Returns the cost between start and finish, given a graph
int CostEstimate( const Graph& aGraph, const Vertex& start, const Vertex& finish)
...

// Member function of a graph
std::vector< Edge > v = ...;
// Sort them according to the cost
std::sort( v.begin(),
           v.end(),
           boost::lambda::bind( CostEstimate( (*this),
                                boost::lambda::bind( &Edge::otherSide, &start, boost::lambda::_1),
                                finish))
           <
           boost::lambda::bind( CostEstimate( (*this),
                                boost::lambda::bind( &Edge::otherSide, &start, boost::lambda::_2),
                                finish)));
   
where otherSide is a const function of the class Edge which returns a
"const Vertex&" 

Compiling this results in an error:

error: invalid initialization of reference of type ‘const Vertex&’ from
expression of type ‘const
boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<3, boost::lambda::function_action<3, boost::lambda::detail::unspecified> >, boost::tuples::tuple<const Vertex& (Edge::* const)(const Vertex&)const, const Vertex* const, const boost::lambda::lambda_functor<boost::lambda::placeholder<1> >, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type, boost::tuples::null_type> > >’

TIA

-- 
Groeten,
Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: [phone]
fax: [phone]
web: www.askesis.nl