prs, On reflection, I've decided to cross-list my reply.
If one accepts the axiom that "a picture is worth a thousand words," then it naturally follows that discussion of graphs is always overly prolix.
I recently had a chat with a fellow programmer and attempted to summarize, in semi-layman terms, how the core algorithms of my multi-state-mazes library work. They're pretty simple, but I couldn't do it without paper and pencil.
Sadly, the same reasoning is also applicable to the code of graph libraries.
If a "code-visualizing compiler IDE" existed that would give us "code pictures" (plus conform to the new C++ standard, not ICE, and so on), I'm pretty sure more of us would be using it for all programming projects, not just graph applications. :) But seriously, with graph theory containing several different problem domains (search, network, AI, etc.), a graph library attempting to be generic enough for use in all of them is necessarily complex.
Boost.Graph seems to expose and require an unnecessarily large amount of complexity, though.
If by "exposure" you mean lots of source code, I'll take that complexity any day of the week and twice on Sundays. :) The library does have a rather steep learning curve, especially if you're somewhat unfamiliar with graph theory and/or template programming.
Whereas libraries like Spirit go to great lengths to make hard things easy, BGL seems to try only to make hard things possible.
I haven't looked at the Spirit library yet, so I can't tell you how easy it may be to use it. Perhaps getting your hands on a copy of the Boost Graph Library book will help (I don't have one, so I'm not certain).
The amount of scaffolding required to use BGL for even the simplest of projects often dwarfs the code size of a naive, yet functional, special-purpose implementation.
Special-purpose implementation of a graph library? Or the project? BGL aims to be as generic as the STL, but whereas each STL container deals with essentially one type of element, a graph needs to contain two types: a vertex type and an edge type. Furthermore, while most STL algorithms confine themselves to handling just those STL container elements, most graph algorithms also need the properties of vertices and/or edges as input. BGL delegates some of the responsibility of property storage to the Boost Property Map Library. I'm just glad the developers kept the complexity down to its current level.
While I understand that the BGL is deeply entrenched in boost culture, certain academic circles, and even publications, I nonetheless suggest that BGL lacks the ease of use necessary for widespread adoption.
Having dwelt in the academic circle known as the University of Central Florida, and thus familiar with the theoretical uses of a graph library (plus I've studied some game development apps on the side), I'd like to learn more about how the Real World would want to use BGL.
Even knowing that ease-of-use is not a criterion for acceptance into boost, looking at what is required of the client to use the BGL always leaves me feeling perplexed. Is there any particular reason that a simplified interface is not made available?
Again, I don't know a simple graph problem that requires a simplified graph interface.
Perhaps a container adapter could be packaged with the library allowing a compromise of functionality and flexibility for simplicity?
I thought the boost::vector_as_graph class template served that purpose. Wrap it around a std::vector<EdgeList>, with EdgeList = std::list<unsigned int> (or an edge list container of your choice, so long as the value type is usable as an index in the vector), and you should be good to go.
If a graphing problem is trivial, shouldn't BGL provide a trivial solution? Why are the simplest useful examples several hundred lines of code?
The examples don't seem that big and hard to understand. Of course, quite a few of them have #ifdefs that I could do without since I don't use the compilers in question, but I can live with them.
I apologize for all of my vague criticisms - my intention is not to flame but rather to test the waters.
Your criticisms seem healthy, and I hope my responses are helpful.
It is difficult for me to assess whether the simplicity I yearn for isn't present for stylistic reasons or whether it would rather necessitate a sacrifice of flexibility, functionality or implementation clarity. Nor is it clear to me to what extent these criteria can be compromised to promote clarity of client code. For what it is worth, the kind of ease-of-use I'm imagining might look like:
#include <less_than_10_graph_headers> ... digraph<some_node_type,some_edge_context_type> g; g << "vertex" << make_pair("vertex", "implicit_vertex"); g.add_edge("brother", "sister", "sibling"); if(g.find(make_pair("brother", "sister"))) related = true;
Could someone please elucidate on why it is impossible/impractical/unnecessary/whatever for a graph library to have such an interface?
I believe the potential for ambiguity would hinder this syntax the most. In this case, you'd have to overload operator<< to input both edges and vertices, and what if some_node_type turned out to be std::pair? You couldn't pass in make_pair(vertex,vertex) as an edge then. The same goes for g.find(); is it supposed to find a vertex, an edge, or both? Also, it seems you want to be able to use non-built-in or custom types as vertex IDs. You'll have to build your own custom-type-to-vertex map and bind it to the graph; BGL won't do it for you, to retain its genericity. Incidentally, BGL favors free functions over member functions. The rationale for that can be found in the FAQ <http://www.boost.org/libs/graph/doc/faq.html>.
Should I accept that the BGL is not the magic bullet graph library and move on, or can this kind of simplicity be somehow found within?
Yeah, no magic bullets here. It depends on the problem you are trying to solve. Cromwell Enage __________________________________ Do you Yahoo!? Yahoo! Finance Tax Center - File online. File on time. http://taxes.yahoo.com/filing.html