On Tue, Oct 15, 2024, at 10:04 AM, Hermann Stamm-Wilbrandt via Boost wrote:
First I looked in graph/test. Most times int is used there, only once std::size_t:
property< edge_index_t, int >
Next I looked into graph/example, same picture there.
Ok, I read that example and test might contain stuff that would not go into BGL code. So I looked into graph/include/boost/graph:
Vertex index doesn't have to be a "static" property of a graph. Many graph models don't naturally provide such an index. Instead, it is often an auxiliary structure for a particular (set of) algorithms. The conceptual requirements are documented with the algorithms, e.g. [`copy_graph`](https://www.boost.org/doc/libs/1_86_0/libs/graph/doc/copy_graph.html) says
The vertex index map type must be a model of Readable Property Map and must map the vertex >> descriptors of G to the integers in the half-open range [0,num_vertices(G)).
Any type that satisfies this for your particular application domain will do. In some applications, `uint16_t` would be fine. Of course, in generic or library code, err on the safe side. None of the library algorithms create a default index argument if the graph model doesn't supply it, as far as I can tell. So the user is always in control.