Hi Doug, All excellent points and I really hope it happens in some form :) . The BGL is great BUT yes usability should take more weight. My project manager was all for scrapping using the BGL because of some of these issues. I thought it was worth a couple more days graft to work out solutions because the payback using the BGL would be more than worth it. In my limited experience (2 months now) there are too many trip wires of the sort we are discussing. I got there in the end with my current problem but the axe is still hovering :( Can I add that misuse of graph assignment and a graph copy constructor is possible - corruptible shallow copies are the result. These methods should be given private scope to prevent (mis)use or be correctly implemented G2 = G1 ; // Compiles but NO you must use boost::graph_copy (G1, G2) instead
3) ... so long as we can still get maximal efficiency out of them when index maps are available.
This was exactly what I was asking in the original post, that my suggestion (in some form) be merged into the algorithm such that it is ONLY used if there is no vertex_index property available either by a graph vertex property OR a named parameter input to the algorithm.
4) ... that maintain vertex and edge index maps internally (as does the Python graph type).
I'm doing just this in a wrapper I have around the BGL graph types. So yes there is a problem that I guess others are also working around.
1) Make edge descriptors ordered (via <), so that users can make associative property maps more easily
Well guess what - I had to do this (but it won't work for multigraphs so
it's not complete)!
template<typename EdgeType>
struct EdgeCompare : public std::binary_function
Part of the problem is the language (C++), not the library. However, we may be able to fix this by going to extraordinary lengths. Though I can't say when one of the developers will have the time to do this. It's quite tedious trying to imagine all the ways an algorithm can be misused and try to trick the compiler into giving a good error message. This is one of the reasons I wrote a Ph.D. thesis about a new language.
And Jeremy neglected to mention that we're trying *very* hard to get some extensions into C++0x so that wretched error messages like these will be a thing of the past.
What do to BGL experts/implementers say? Would it not be **saner** to get these algorithms to work automatically no matter what graph type was chosen?
The problem with std::map is that it does not provide constant time access to the vertex index (it is logarithmic). Thus, the graph algorithm will run slower; it won't have the advertised time complexity. Then we'll get bug reports from people that are surprised by how slow the algorithm is.
It's definitely slower, but I think we need to give the usability
issue more weight. I only recall ever having seen two cases where
someone complained about the BGL being to slow: one was with
betweenness_centrality, until we learned that the person had compiled
without any optimizations; the other was with bundled properties
slowing things down (due to the extra level of dispatch). On the
other hand, we get questions every week about how to create property
maps, especially edge property maps (because there's no way to avoid
managing your own edge_index_t). We should get users hooked on the
BGL first, then we can worry about getting maximal performance for
them later.
I've been thinking of a few ways to try to help users with creating
and using property maps. It's possible that "all of them" is the
right answer:
1) Make edge descriptors ordered (via <), so that users can make
associative property maps more easily
2) Create templates vertex_property_map