Re: [Boost-users] PropertyGraphConcept concept checking errors for an example implicit graph

Subject: Re: [Boost-users] PropertyGraphConcept concept checking errors for an example implicit graph
From: W.P. McNeill (billmcn_at_[hidden])
Date: 2010-06-24 20:22:58

Thanks for your help.  Getting a little closer.

Once I get the edge properties working I'll look at traversal concepts other
than AdjacencyGraphs.  So far this has been the easy part for me.

I have been looking at the grid graph, but I couldn't figure out how to add
weights to the edges of a grid graph.  I can't find a simple example of an
implicit graph with properties.  (Which is why I'm trying to write one now.)

What do you mean by "Write an empty struct that inherits from all of the
ones that you are going to model"?  I didn't think there were concept base
classes to inherit from.

Changing the property typedef in the implicit graph struct to

    typedef boost::property<boost::edge_weight_t, float> edge_property_type;

making the get() functions take constant graph object references, and
checking against the ReadablePropertyGraphConcept improves the compilation.
 I now no longer have pages of errors, which makes me think I'm on the right
track.

I still have two errors, both of which I'm confused about.

1. graph_concepts.hpp:390: error: conversion from ‘EdgeWeightMap’ to
non-scalar type ‘boost::typed_identity_property_map<size_t>’ requested

This is the same as before.  This error makes me feel like I've got the
wrong return value for one of my get() functions, but after double-checking
they look right.

2. property_map.hpp:318: error: no match for ‘operator[]’ in ‘(const
boost::typed_identity_property_map<size_t>&)((const
boost::typed_identity_property_map<size_t>*)(& pa))[k]’

I didn't think any concept required operator[], so I'm not sure why this is
happening.  Line 318 is inside the inline get() function of
the put_get_helper(), but I'm not using put_get_helper() in my code.

On Thu, Jun 24, 2010 at 1:25 PM, W.P. McNeill <billmcn_at_[hidden]> wrote:

> I am writing a stripped-down implicit graph that I hope can be a useful
> template for others working with the Boost Graph library.  The project is
> hosted at github.  Excerpts from the source are in this email, and the full
> source is viewable online at
> http://github.com/wpm/Boost-Implicit-Graph-Example.
>
> I am currently getting errors from the concept checking code which I don't
> understand and am looking for suggestions as to what I am doing wrong.
>
> This is graph class.
>
> struct ImplicitRingGraph {
> ImplicitRingGraph(size_t n):n(n) {};
>
> // Graph concept
>  typedef size_t vertex_descriptor;
> typedef boost::undirected_tag directed_category;
>  typedef boost::disallow_parallel_edge_tag edge_parallel_category;
> typedef boost::adjacency_graph_tag traversal_category;
>
> // AdjacencyGraph concept
> typedef RingAdjacencyIterator adjacency_iterator;
>
> // PropertyGraph concept
> typedef boost::edge_weight_t edge_property_type;
>
> // Additional types required by the concept-checking code.
> typedef std::pair<vertex_descriptor, vertex_descriptor> edge_descriptor;
>  typedef size_t vertices_size_type;
> typedef size_t edges_size_type;
> typedef size_t degree_size_type;
>  typedef void out_edge_iterator;
> typedef void in_edge_iterator;
>  typedef void vertex_iterator;
> typedef void edge_iterator;
>
> // The number of vertices in the graph.
>  size_t n;
> };
> typedef boost::graph_traits<ImplicitRingGraph>::edge_descriptor Edge;
>
>
> I want the edges to have weights, so it models the PropertyGraph concept.
>  The following functions implement the valid expressions.
>
>
> EdgeWeightMap get(boost::edge_weight_t, ImplicitRingGraph& g) {
>  return EdgeWeightMap();
> }
>
>
> EdgeWeight get(boost::edge_weight_t tag, ImplicitRingGraph& g, Edge e) {
>  return get(tag, g)[e];
> }
>
>
> (Definitions of Edge, EdgeWeight, and EdgeWeightMap are visible online.  I
> also define an adjacency iterator that is not shown here.)
>
> I can write code that reads an edge weight.
>
> ImplicitRingGraph g(5);
>  EdgeWeightMap m = get(boost::edge_weight, g);
> boost::graph_traits<ImplicitRingGraph>::edge_descriptor e(0, 1);
>  EdgeWeight w = get(boost::edge_weight, g, e);
>
> However I get errors when I try to use the concept checking code.
>
>  function_requires<
> PropertyGraphConcept<ImplicitRingGraph,
>  Edge,
>  edge_weight_t>
> >();
>
>
> The full error printout is huge, but there appear to be three relevant
> problems.
>
> 1. graph_concepts.hpp:406: error: conversion from ‘EdgeWeightMap’ to
> non-scalar type ‘boost::typed_identity_property_map<size_t>’ requested
>
> The line in graph_concepts.hpp is
>
>         Map pmap = get(Property(), g);
>
> inside the concept check for PropertyGraph.  It looks to me like I have a
> function to handle this.  I don't understand
> where boost::typed_identity_property_map<size_t> is coming from.
>
>
> 2. graph_concepts.hpp:408: error: no matching function for call to
> ‘put(boost::edge_weight_t, ImplicitRingGraph&, Edge&, size_t&)’
>
> I didn't write any put() functions so I understand why I'm getting this.
>  However, I would like the edge weights to be readable but not writeable
> (myEdgeWeightMap models a ReadablePropertyMap), and I can't figure out how
> to specify the read-only property in the graph defintion.
>
>
> 3. graph_concepts.hpp:390: error: no matching function for call to
> ‘get(boost::edge_weight_t, const ImplicitRingGraph&)’
> graph_concepts.hpp:391: error: no matching function for call to
> ‘get(boost::edge_weight_t, const ImplicitRingGraph&, Edge&)’
>
> Should I create functions identical to what  I've already written, except
> with constant modifiers in front of the graph type?  That feels like
> redundant source.
>
>
> Thanks for any help you can give.  Hopefully, a completed version of this
> example would be a useful resource for other BGL developers.
>