Re: [boost] [parameter] type requirement compiler error

Subject: Re: [boost] [parameter] type requirement compiler error
From: Lorenzo Caminiti (lorcaminiti_at_[hidden])
Date: 2011-11-03 20:04:18

I'm sorry for spamming requests for help every day... I'm really stuck
here and any help would be very welcome :) Please let me know if I
need to clarify my question better. Thanks!

On Wed, Nov 2, 2011 at 6:51 PM, Lorenzo Caminiti <lorcaminiti_at_[hidden]> wrote:
> On Wed, Nov 2, 2011 at 4:40 PM, Lorenzo Caminiti <lorcaminiti_at_[hidden]> wrote:
>> On Mon, Oct 24, 2011 at 2:16 PM, Dave Abrahams <dave_at_[hidden]> wrote:
>>>
>>> on Mon Oct 24 2011, lcaminiti <lorcaminiti-AT-gmail.com> wrote:
>>>
>>>> Hello all,
>>>>
>>>> The following parameter type requirement:
>>>>
>>>>     (required (graph, *) )
>>>>     (optional (root_vertex,
>>>>                 (typename
>>>> boost::graph_traits<graph_type>::vertex_descriptor),
>>>>                 *boost::vertices(graph).first) )
>>>>
>>>> Generates a GCC error:
>>>>
>>>> dfs.05.cpp:40: error: ‘graph_type’ was not declared in this scope
>>>
>>> Yeah.... I'm guessing this is what graphs::graph::_ is all about, but
>>> according to revision control, Daniel made this happen, and there's
>>> basically no documentation for it.  Daniel?
>>
>> Help anyone??
>>
>> I'm just trying to compile the graph example from the Boost.Parameter
>> docs, in an ideal world (doc examples added to regression tests) it'd
>> be easier... please help :)
>
> Here's the deal. If I use tag::graph::_ instead of graph_type, that
> type is define by the expansion of BOOST_PARAMETER_NAME(graph) as:
>
> namespace tag {
>    struct graph {
>        static char const* keyword_name() { return "graph"; }
>        typedef boost::parameter::value_type< boost::mpl::_2, graph,
> boost::parameter::void_ > _;
>        typedef boost::parameter::value_type< boost::mpl::_2, graph,
> boost::parameter::void_ > _1;
>    };
> }
> namespace {
>    ::boost::parameter::keyword<tag::graph> const& _graph =
> ::boost::parameter::keyword<tag::graph>::instance;
> }
>
> Then if I use this type in the declaration of the root_vertex parameter type:
>
>    (optional
>        (root_vertex,
>                (typename
> boost::graph_traits<tag::graph::_>::vertex_descriptor),
>                *boost::vertices(graph).first)
>        )
>    )
>
> I get the error:
>
> /usr/include/boost/parameter/value_type.hpp: In instantiation of
> ‘boost::parameter::value_type<mpl_::arg<2>, graphs::tag::graph,
> boost::parameter::void_>’:
> /usr/include/boost/graph/graph_traits.hpp:29:52:   instantiated from
> ‘boost::graph_traits<boost::parameter::value_type<mpl_::arg<2>,
> graphs::tag::graph, boost::parameter::void_> >’
> dfs.06.cpp:85:1:   instantiated from here
> /usr/include/boost/parameter/value_type.hpp:60:13: error: no type
> named ‘binding’ in ‘struct mpl_::arg<2>’
> /usr/include/boost/parameter/value_type.hpp:62:5: error: no type named
> ‘binding’ in ‘struct mpl_::arg<2>’
>
> I am not sure but it seems that the mpl::_2 in graph::_ declaration is
> not bound to anything while it should be bound to Boost.Parameter
> argument pack... how is this supposed to work? Who should bind mpl::_2
> to the argument pack?
>
> Thanks a lot.
> --Lorenzo
>

--Lorenzo