bug #1774: fix VectorwiseOp::begin()/end() return types regarding constness.

Eigen/src/Core/VectorwiseOp.h

diff --git a/Eigen/src/Core/VectorwiseOp.h b/Eigen/src/Core/VectorwiseOp.h
index db0b9f8..274501c 100644
--- a/Eigen/src/Core/VectorwiseOp.h
+++ b/Eigen/src/Core/VectorwiseOp.h
@@ -1,7 +1,7 @@
 // This file is part of Eigen, a lightweight C++ template library
 // for linear algebra.
 //
-// Copyright (C) 2008-2010 Gael Guennebaud <gael.guennebaud@inria.fr>
+// Copyright (C) 2008-2019 Gael Guennebaud <gael.guennebaud@inria.fr>
 // Copyright (C) 2006-2008 Benoit Jacob <jacob.benoit.1@gmail.com>
 //
 // This Source Code Form is subject to the terms of the Mozilla
@@ -286,14 +286,18 @@
     /** returns an iterator to the first row (rowwise) or column (colwise) of the nested expression.
       * \sa end(), cbegin()
       */
-    iterator        begin() const { return iterator      (m_matrix, 0); }
+    iterator        begin()       { return iterator      (m_matrix, 0); }
+    /** const version of begin() */
+    const_iterator  begin() const { return const_iterator(m_matrix, 0); }
     /** const version of begin() */
     const_iterator cbegin() const { return const_iterator(m_matrix, 0); }
 
     /** returns an iterator to the row (resp. column) following the last row (resp. column) of the nested expression
       * \sa begin(), cend()
       */
-    iterator        end()   const { return iterator      (m_matrix, m_matrix.template subVectors<DirectionType(Direction)>()); }
+    iterator        end()         { return iterator      (m_matrix, m_matrix.template subVectors<DirectionType(Direction)>()); }
+    /** const version of end() */
+    const_iterator  end()   const { return const_iterator(m_matrix, m_matrix.template subVectors<DirectionType(Direction)>()); }
     /** const version of end() */
     const_iterator cend()   const { return const_iterator(m_matrix, m_matrix.template subVectors<DirectionType(Direction)>()); }
 

test/stl_iterators.cpp

diff --git a/test/stl_iterators.cpp b/test/stl_iterators.cpp
index 5fef34c..cdd9e5c 100644
--- a/test/stl_iterators.cpp
+++ b/test/stl_iterators.cpp
@@ -1,12 +1,13 @@
 // This file is part of Eigen, a lightweight C++ template library
 // for linear algebra.
 //
-// Copyright (C) 2018 Gael Guennebaud <gael.guennebaud@inria.fr>
+// Copyright (C) 2018-2019 Gael Guennebaud <gael.guennebaud@inria.fr>
 //
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+#include <iterator>
 #include <numeric>
 #include "main.h"
 
@@ -422,6 +423,16 @@
     VERIFY_IS_EQUAL( std::find_if(A.colwise().begin(), A.colwise().end(), [](typename ColMatrixType::ColXpr x) { return x.norm() == Scalar(0); })-A.colwise().begin(), j );
   }
 
+  {
+    using VecOp = VectorwiseOp<ArrayXXi, 0>;
+    STATIC_CHECK(( internal::is_same<VecOp::const_iterator, decltype(std::declval<const VecOp&>().cbegin())>::value ));
+    STATIC_CHECK(( internal::is_same<VecOp::const_iterator, decltype(std::declval<const VecOp&>().cend  ())>::value ));
+    #if EIGEN_COMP_CXXVER>=14
+      STATIC_CHECK(( internal::is_same<VecOp::const_iterator, decltype(std::cbegin(std::declval<const VecOp&>()))>::value ));
+      STATIC_CHECK(( internal::is_same<VecOp::const_iterator, decltype(std::cend  (std::declval<const VecOp&>()))>::value ));
+    #endif
+  }
+
 #endif
 }