id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
511	predicates without default constructor fail to compile	nobody	nobody	"{{{
  I want to draw your attention to a possible flaw in the 
implementation of the write_graphviz method from the 
Boost Graph Library.

  The current implementation uses the assignment 
operator for the vertex and edge iterators. This is natural, 
but some examples fail to compile with
this version. The problem comes from the predicates 
witch don't have default constructors. 

  When trying to assign a vertex iterator of a graph 
filtered with such a predicate, the compiler issues an 
error:

C2512:'positive_edge_weight_pred<MyEdgeWeightMap>'
 : no appropriate default constructor available
        with
        [
            MyEdgeWeightMap=EdgeWeightMapT
        ]

  If a small modification in the write_graphviz 
implementation is made (using copy constructors 
instead of assignement operators), the example 
compiles and runs sucesfully. I am using the Microsoft 
Visual C++ 7.1 compiler.

  In conclusion, I think that this modification should be 
made, as it grows the flexibility of the library and doesn't 
add any overhead.

  I have attached the example (main.cpp) and the patch 
for graphviz.hpp (graphviz.hpp.patch).

  My e-mail adress is pdumitrache@bphx.ro
}}}"	Bugs	closed		graph	None		Duplicate