From 392b95bdf135cd991f6d09c5ff3b1bd2f01fb5f4 Mon Sep 17 00:00:00 2001
From: Louis David <gitlab@louisdavid.fr>
Date: Thu, 6 Jun 2024 21:38:09 +0000
Subject: [PATCH] allow pointer_based_stl_iterator to conform to the
 contiguous_iterator concept if we are in c++20

---
 Eigen/src/Core/StlIterators.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Eigen/src/Core/StlIterators.h b/Eigen/src/Core/StlIterators.h
index 3ab7d2101..bb897f8c6 100644
--- a/Eigen/src/Core/StlIterators.h
+++ b/Eigen/src/Core/StlIterators.h
@@ -325,7 +325,13 @@ class pointer_based_stl_iterator {
  public:
   typedef Index difference_type;
   typedef typename XprType::Scalar value_type;
+#if __cplusplus >= 202002L
+  typedef std::conditional_t<XprType::InnerStrideAtCompileTime == 1, std::contiguous_iterator_tag,
+                             std::random_access_iterator_tag>
+      iterator_category;
+#else
   typedef std::random_access_iterator_tag iterator_category;
+#endif
   typedef std::conditional_t<bool(is_lvalue), value_type*, const value_type*> pointer;
   typedef std::conditional_t<bool(is_lvalue), value_type&, const value_type&> reference;