From db9a9a12ba25353c94417dba24fab35cee16bde1 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Fri, 9 Nov 2018 16:49:19 +0100
Subject: bug #1619: make const and non-const iterators compatible

---
 Eigen/src/Core/StlIterators.h | 40 ++++++++++++++++++++++++++++++++++------
 1 file changed, 34 insertions(+), 6 deletions(-)

(limited to 'Eigen/src/Core/StlIterators.h')

diff --git a/Eigen/src/Core/StlIterators.h b/Eigen/src/Core/StlIterators.h
index 24eef1269..e39decc85 100644
--- a/Eigen/src/Core/StlIterators.h
+++ b/Eigen/src/Core/StlIterators.h
@@ -57,6 +57,11 @@ template<typename XprType>
 class pointer_based_stl_iterator
 {
   enum { is_lvalue  = internal::is_lvalue<XprType>::value };
+  typedef pointer_based_stl_iterator<typename internal::remove_const<XprType>::type > non_const_iterator;
+  typedef pointer_based_stl_iterator<typename internal::add_const<XprType>::type > const_iterator;
+  typedef typename internal::conditional<internal::is_const<XprType>::value,non_const_iterator,const_iterator>::type other_iterator;
+  friend const_iterator;
+  friend non_const_iterator;
 public:
   typedef Index difference_type;
   typedef typename XprType::Scalar value_type;
@@ -64,12 +69,24 @@ public:
   typedef typename internal::conditional<bool(is_lvalue), value_type*, const value_type*>::type pointer;
   typedef typename internal::conditional<bool(is_lvalue), value_type&, const value_type&>::type reference;
 
+
   pointer_based_stl_iterator() : m_ptr(0) {}
   pointer_based_stl_iterator(XprType& xpr, Index index) : m_incr(xpr.innerStride())
   {
     m_ptr = xpr.data() + index * m_incr.value();
   }
 
+  pointer_based_stl_iterator(const non_const_iterator& other)
+    : m_ptr(other.m_ptr), m_incr(other.m_incr)
+  {}
+
+  pointer_based_stl_iterator& operator=(const non_const_iterator& other)
+  {
+    m_ptr = other.m_ptr;
+    m_incr.setValue(other.m_incr);
+    return *this;
+  }
+
   reference operator*()         const { return *m_ptr;   }
   reference operator[](Index i) const { return *(m_ptr+i*m_incr.value()); }
   pointer   operator->()        const { return m_ptr;    }
@@ -92,12 +109,23 @@ public:
     return (m_ptr - other.m_ptr)/m_incr.value();
   }
 
-  bool operator==(const pointer_based_stl_iterator& other) { return m_ptr == other.m_ptr; }
-  bool operator!=(const pointer_based_stl_iterator& other) { return m_ptr != other.m_ptr; }
-  bool operator< (const pointer_based_stl_iterator& other) { return m_ptr <  other.m_ptr; }
-  bool operator<=(const pointer_based_stl_iterator& other) { return m_ptr <= other.m_ptr; }
-  bool operator> (const pointer_based_stl_iterator& other) { return m_ptr >  other.m_ptr; }
-  bool operator>=(const pointer_based_stl_iterator& other) { return m_ptr >= other.m_ptr; }
+  difference_type operator-(const other_iterator& other) const {
+    return (m_ptr - other.m_ptr)/m_incr.value();
+  }
+
+  bool operator==(const pointer_based_stl_iterator& other) const { return m_ptr == other.m_ptr; }
+  bool operator!=(const pointer_based_stl_iterator& other) const { return m_ptr != other.m_ptr; }
+  bool operator< (const pointer_based_stl_iterator& other) const { return m_ptr <  other.m_ptr; }
+  bool operator<=(const pointer_based_stl_iterator& other) const { return m_ptr <= other.m_ptr; }
+  bool operator> (const pointer_based_stl_iterator& other) const { return m_ptr >  other.m_ptr; }
+  bool operator>=(const pointer_based_stl_iterator& other) const { return m_ptr >= other.m_ptr; }
+
+  bool operator==(const other_iterator& other) const { return m_ptr == other.m_ptr; }
+  bool operator!=(const other_iterator& other) const { return m_ptr != other.m_ptr; }
+  bool operator< (const other_iterator& other) const { return m_ptr <  other.m_ptr; }
+  bool operator<=(const other_iterator& other) const { return m_ptr <= other.m_ptr; }
+  bool operator> (const other_iterator& other) const { return m_ptr >  other.m_ptr; }
+  bool operator>=(const other_iterator& other) const { return m_ptr >= other.m_ptr; }
 
 protected:
 
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