Re: [Boost-users] boost.graph question concerning edge descriptor details

From: Doug Gregor (dgregor_at_[hidden])
Date: 2004-08-23 13:25:00

On Aug 23, 2004, at 11:30 AM, Jeff Holle wrote:

> I may have answered my own question.
> The Compare functor that does the trick is:
>  struct ltExternalEdge : public 
> std::binary_function<ExternalEdge,ExternalEdge, bool> {
>    bool operator()(const ExternalEdge& __x, const ExternalEdge& __y) 
> const
>    {
>    return (__x.first < __y.first || (!(__y.first < __x.first) && 
> __x.second.get_property() < __y.second.get_property())) ? true : 
> false;
>    }
>  };
>
> Is such a Compare operator safe?  Note that I'm note using internal 
> properties.

This is not guaranteed to work, because edge descriptors aren't 
required to have the "get_property" or "first" members. Practically 
speaking, I think it will work, but can't be sure.

> It would be really nice if the object that edge_iterator references
> implemenented a operator< method.
> Then it would work seamlessly with the std::pair operator< method, 
> which
> I pretty much copied in the above code.

I'm not sure that this can always be implemented efficiently, but it 
surely would be useful.

        Doug