Hi Chris, On Mon, 16 Sep 2002, Chris Russell wrote: cdr> Okay - I think I understand this. Since posting I've re-read the cdr> property map documentation online and in the book and am still cdr> confused about several points (forgive me ignorance - I'm learning a cdr> lot of new concepts (in the canonical sense) at once). Will you help cdr> me with these follow-up questions please: cdr> cdr> Assertions: (please validate) cdr> cdr> 1. a property map maps some type (an enum or struct tag) to some other cdr> type. No, a propery map is a map from a set of key objects to a set of value objects. What you are probably thinking about is the boost::get() function that returns a property map for a given graph and property tag. Perhaps it is a little confusing that you use a different overload of boost::get() on the property map itself. cdr> 2. a property map declaration may contain nested property map cdr> declarations but this does not reflect a hierarchy - it's just a cdr> template trick. Effectively the property maps are peers. Hmm, the above statement doesn't make much sense to me. cdr> 3. graph containers like adjacency list will internally create a new cdr> value_type object upon insertion of a vertex (in the case of a vertex cdr> property map) and an edge (in the case of an edge property map). Yes. cdr> Assuming the above assertions are correct, I'm still confused about cdr> several points: cdr> cdr> 1. a boost::get call to return either a property_map<x,y>::type or cdr> property_map<x,y>::const_type by value? I think yes. The question is does cdr> return by value also copy all the value_type's? I'm guessing not because cdr> this would be a huge performance hit. Just the property map itself is cdr> copied. Correct? The copy semantics for property maps is required to be shallow, so that copying is lightweight. In browsing through the online property map docs it looks like I forgot to make that explicit. cdr> 2. In the case of my algorithm visitor, I am passed a const reference cdr> to a graph that will result in a boost::get returning a const_type a cdr> property map. I can understand that changing the value_type's of an cdr> arbitrary property map could potentially screw up an algorithm (if cdr> the algorithm is using the specific property that I am trying to cdr> write). Is this why the graph passed to the visitor is const? In the cdr> case where I need to write an internal property map that is not being cdr> used by the specific algorithm (in the case of my dfs search, dfs is cdr> using the vertex color and I want to write another, distinct internal cdr> property map that I have registered with my graph class), I should cdr> pass a reference to the specific map into the constructor of the cdr> visitor? Yes, that would work. cdr> Thank you for your help Jeremy. You bet! Cheers, Jeremy ---------------------------------------------------------------------- Jeremy Siek http://php.indiana.edu/~jsiek/ Ph.D. Student, Indiana Univ. B'ton email: jsiek@osl.iu.edu C++ Booster (http://www.boost.org) office phone: (812) 855-3608 ----------------------------------------------------------------------