[boost] Named params library and BGL

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-04-15 05:56:46

I've just made an attempt to use the named parameters library (currently in 
review queue, and available at 
http://groups.yahoo.com/group/boost/files/named_params.zip) to simply 
properties in BGL.

Currently, to initialize all properties one has to do:

    edge_descriptor e = add_edge(....);
    put(e, g, vertex_color, 10);
    put(e, g, vertex_name, "foo");

I hope that with the named parameters library it will be possible to do:

   add_edge(v1, v2, (vertex_color = 10, vertex_name = "foo"), g);

I've tried to implement this idea, but run into the problems. First issue is 
documentation: it gives

    foo_impl(foo_keywords(a0));

as example, while the code uses:

   return f_impl(f_keywords()(t, name_));

Which has extra '()' after f_keywords.

The second problem is that I need to create a type for 'keywords' (derived 
from 'keywords<...>' and use it for passing arguments).  The docs suggest to 
create a number of forwarding functions, but given that a number of vertex 
properties can be rather large (and is actually unbounded), this does not 
seem good.

So, now can do:

    vertex_property p = prop_keywords()(color = 10, name = "foo");

but I'd rather like:

    vertex_property p((color = 10, name = "foo"));

So, the operator, will be overloaded to create something I can index with 'tag 
type' and get a value. In fact, this will allow to avoid declaring 
'pop_keywords' -- since again, user can declare it's own keywords so it's not 
clear how to define that class.

The example I've played with is at:
 
     http://zigzag.cs.msu.su:7813/p.cpp

Comments are appreciated.

- Volodya