[Boost-users] [BGL] Can't set non-const edge_descriptor = const edge_descriptor

Subject: [Boost-users] [BGL] Can't set non-const edge_descriptor = const edge_descriptor
From: John Robertson (jrobertson7711_at_[hidden])
Date: 2010-09-04 00:56:49

I have

struct edge_properties
{
    Traits::edge_descriptor ePredecessor;
}

some_function ( const Graph g )
{

    e = edge(vertex_a, vertex_b, g).first;

    //fails here
    g[e].ePredecessor = e;

}

compiler gives

./Includes/Utilities.cpp:451: error: passing ‘const 
boost::detail::edge_desc_impl<boost::bidirectional_tag, long unsigned int>’ as 
‘this’ argument of ‘boost::detail::edge_desc_impl<boost::bidirectional_tag, long 
unsigned int>& boost::detail::edge_desc_impl<boost::bidirectional_tag, long 
unsigned int>::operator=(const 
boost::detail::edge_desc_impl<boost::bidirectional_tag, long unsigned int>&)’ 
discards qualifiers
make: *** [pl] Error 1

My guess is that e is returned as a const but g[e].ePredecessor is declared a 
variable.
How can I fix this?

Thanks
John