RE: [Boost-users] graph peculiarities

From: Arias Brent-P96059 (Brent.Arias_at_[hidden])
Date: 2005-03-14 18:16:33

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The "install property" approach has some advantages when creating 
property maps for internal properties. For instance, you can determine 
if there is an "edge_weight" property and use it, without poking into 
the user-supplied type for the edges.
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Ok, I can see that.

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I don't know the rationale for the original design, but I will also 
note that bundled properties don't (and can't) work on Visual C++ 6.0, 
a compiler that had to be supported when the BGL was released.
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Do bundled properties now work with the C++ compiler of Visual Studio.NET (i.e. version 7)?

> What were you expecting instead of vertex 
descriptors?

Keep in mind I'm a newbie to the Graph lib, but my answer is that I'd just dispense with the descriptors, and absorb the functionality straight into the iterators.  So, for example, a call to 

source(e, g) 

...would have 'e' refer to an edge iterator rather than an edge descripter.  I could guess why that approach wasn't taken, but if you happen to know - please do tell.  :)

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I'm not sure the std::map<string, int> analogy holds up well, because 
accessing the int for a given string requires logarithmic time, which 
would not be acceptable for a graph. Using vertex descriptors allows 
the library to reference vertices without regard to their storage (or 
storage of their properties).
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Ok, my bad analogy aside, isn't it also true that iterators similarly allow reference to vertices / edges without regard to their storage?  Keep in mind that, as far as I can tell, you can't retrive a vertex_descripter until you've retrieved a vertex_iterator.  So it appears you are dependent on iterators either way.

But I suppose I don't fully appreciate the restrictions the designers faced.  For example, consider the description of functor "exercise_vertex()" found here:

http://boost.org/libs/graph/doc/quick_tour.html

...that makes me wonder if the descripter was simply a syntactic necessity (that an iterator could not fulfill).  Thoughts?

-Brent