From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Thu, 23 May 2024 19:54:18 +0000 (-0600)
Subject: Work around a BOOST issue with C++20.
X-Git-Tag: v9.6.0-rc1~229^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=748c08b83c2724e57a963e9d463621e2414a5bbc;p=dealii.git

Work around a BOOST issue with C++20.
---

diff --git a/include/deal.II/numerics/rtree.h b/include/deal.II/numerics/rtree.h
index d132a6d9f5..2ee8a697f6 100644
--- a/include/deal.II/numerics/rtree.h
+++ b/include/deal.II/numerics/rtree.h
@@ -498,9 +498,17 @@ RTree<typename ContainerType::size_type,
       IndexableGetterFromIndices<ContainerType>>
 pack_rtree_of_indices(const ContainerType &container)
 {
-  std_cxx20::ranges::iota_view<typename ContainerType::size_type,
-                               typename ContainerType::size_type>
-    indices(0, container.size());
+  // We need an array that holds the indices we want to pack. The rtree
+  // implementation in BOOST, for reasons not entirely clear, insists
+  // on using a reference to the elements of the range. This is fine if
+  // the indices are stored in a container, so that's what we do.
+  // (It would be nice if we could just pass a std::ranges::iota_view
+  // instead, but that has no nested 'reference' type, and this then
+  // trips up BOOST rtree.)
+  std::vector<typename ContainerType::size_type> indices(container.size());
+  for (typename ContainerType::size_type i = 0; i < container.size(); ++i)
+    indices[i] = i;
+
   return RTree<typename ContainerType::size_type,
                IndexType,
                IndexableGetterFromIndices<ContainerType>>(