From 2bf1a31d811fef2085bad97f98e2d0095136b636 Mon Sep 17 00:00:00 2001
From: Eugene Zhulenev <ezhulenev@google.com>
Date: Wed, 10 Oct 2018 10:31:40 -0700
Subject: [PATCH] Use void type if stl-style iterators are not supported

---
 Eigen/src/Core/DenseBase.h                |  4 ++--
 Eigen/src/Core/StlIterators.h             | 13 -------------
 Eigen/src/Core/util/ForwardDeclarations.h |  1 -
 3 files changed, 2 insertions(+), 16 deletions(-)

diff --git a/Eigen/src/Core/DenseBase.h b/Eigen/src/Core/DenseBase.h
index eedeacc94..2a0927317 100644
--- a/Eigen/src/Core/DenseBase.h
+++ b/Eigen/src/Core/DenseBase.h
@@ -594,12 +594,12 @@ template<typename Derived> class DenseBase
 
     typedef typename internal::conditional< IsVectorAtCompileTime,
                                             iterator_type,
-                                            internal::not_an_iterator<const Derived>
+                                            void
                                           >::type iterator;
 
     typedef typename internal::conditional< IsVectorAtCompileTime,
                                             const_iterator_type,
-                                            internal::not_an_iterator<const Derived>
+                                            void
                                           >::type const_iterator;
     #endif
 
diff --git a/Eigen/src/Core/StlIterators.h b/Eigen/src/Core/StlIterators.h
index 5f2edc4e6..24eef1269 100644
--- a/Eigen/src/Core/StlIterators.h
+++ b/Eigen/src/Core/StlIterators.h
@@ -11,19 +11,6 @@ namespace Eigen {
 
 namespace internal {
 
-// Iterator type for XprType that do not support stl-style iterators. Allows to
-// detect that expression does not support stl iterators at compile time.
-template<typename XprType>
-class not_an_iterator
-{
-  not_an_iterator() : mp_xpr(0), m_index(0) {}
-  not_an_iterator(XprType& xpr, Index index) : mp_xpr(&xpr), m_index(index) {}
-
- protected:
-  XprType *mp_xpr;
-  Index m_index;
-};
-
 template<typename XprType,typename Derived>
 class indexed_based_stl_iterator_base
 {
diff --git a/Eigen/src/Core/util/ForwardDeclarations.h b/Eigen/src/Core/util/ForwardDeclarations.h
index 49c4e0c31..3ab3a5f50 100644
--- a/Eigen/src/Core/util/ForwardDeclarations.h
+++ b/Eigen/src/Core/util/ForwardDeclarations.h
@@ -135,7 +135,6 @@ template<typename Derived> class SolverBase;
 template<typename XprType> class InnerIterator;
 
 namespace internal {
-template<typename XprType> class not_an_iterator;
 template<typename XprType> class generic_randaccess_stl_iterator;
 template<typename XprType> class pointer_based_stl_iterator;
 template<typename XprType, DirectionType Direction> class subvector_stl_iterator;