Boost Graph - adjacency_list in_edge_iterator are only input_iterator_tag?
Hi, Hopefully this is the right place for this. This with Boost 1.81.0 It looks like boost::adjacency_list's in_edge_iterator, out_edge_iterator, and for bidirectional graphs also edge_iterator all are only input iterators. This seems a bit restrictive, and is regardless of the type of EdgeList template parameter. For example, this code (which seems a relatively reasonable thing to want to do) doesn't work: https://godbolt.org/z/n3PdEYo49 It doesn't work because transform_view doesn't define iterator_category if the iterator is not at least a forward iterator (I'm a bit confused as to why that is, but that's not a boost-related thing). I did some digging and found out why the iterator is always an input iterator: The iterators are defined as following: template < class BaseIter, class VertexDescriptor, class EdgeDescriptor, class Difference > struct in_edge_iter : iterator_adaptor< in_edge_iter< BaseIter, VertexDescriptor, EdgeDescriptor, Difference >, BaseIter, EdgeDescriptor, use_default, EdgeDescriptor, Difference
{ // .... }; EdgeDescriptor is passed in as the reference type, but it is not a reference so the iterator adaptor always chooses input_iterator_tag for the iterator_category. Does anyone know of a workaround, or know if this is the desired behavior for edge iterators? Am I missing something obvious here? Thank you very much, Nicolas Morales
It doesn't sound ideal. So is it just missing the & in the list of template arguments to iterator_adaptor? Jeremy On Sun, 5 May 2024 at 09:48, Nic via Boost-users < boost-users@lists.boost.org> wrote:
Hi, Hopefully this is the right place for this. This with Boost 1.81.0 It looks like boost::adjacency_list's in_edge_iterator, out_edge_iterator, and for bidirectional graphs also edge_iterator all are only input iterators.
This seems a bit restrictive, and is regardless of the type of EdgeList template parameter. For example, this code (which seems a relatively reasonable thing to want to do) doesn't work: https://godbolt.org/z/n3PdEYo49
It doesn't work because transform_view doesn't define iterator_category if the iterator is not at least a forward iterator (I'm a bit confused as to why that is, but that's not a boost-related thing).
I did some digging and found out why the iterator is always an input iterator:
The iterators are defined as following:
template < class BaseIter, class VertexDescriptor, class EdgeDescriptor, class Difference > struct in_edge_iter : iterator_adaptor< in_edge_iter< BaseIter, VertexDescriptor, EdgeDescriptor, Difference >, BaseIter, EdgeDescriptor, use_default, EdgeDescriptor, Difference > { // .... };
EdgeDescriptor is passed in as the reference type, but it is not a reference so the iterator adaptor always chooses input_iterator_tag for the iterator_category.
Does anyone know of a workaround, or know if this is the desired behavior for edge iterators? Am I missing something obvious here?
Thank you very much, Nicolas Morales _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org https://lists.boost.org/mailman/listinfo.cgi/boost-users
participants (2)
-
Jeremy Murphy -
Nic