[boost] [BGL] [Property Map] PropertyGraph concept

26 Oct 2009

      Hi to all,

I've taked a look to the PropertyGraph concept, and it defines the 
following valid expression:

     get(p, g, x)

and its return type:

     boost::property_traits<Map>::*value_type*

Also the docs of Property Map library says that the get() function 
return the property *by value*, making a copy of the property.

But looking to the \boost\graph\detail\adjacency_list.hpp file, I've 
noticed that the return value of the get function is:

     typename boost::property_traits<
       typename boost::property_map<typename Config::graph_type,
         Property>::type
     >::*reference*

Why this difference? Or they are the same think?

Which is the correct specific?

Thanks in advance,
Cosimo Calabrese.