Protect c++11 type alias with Eigen's macro, and add respective unit test.

Eigen/src/Core/Array.h

diff --git a/Eigen/src/Core/Array.h b/Eigen/src/Core/Array.h
index 039f41a..a85d508 100644
--- a/Eigen/src/Core/Array.h
+++ b/Eigen/src/Core/Array.h
@@ -350,7 +350,7 @@
 #undef EIGEN_MAKE_ARRAY_TYPEDEFS_ALL_SIZES
 #undef EIGEN_MAKE_ARRAY_TYPEDEFS
 
-#if __cplusplus>=201103L
+#if EIGEN_HAS_CXX11
 
 #define EIGEN_MAKE_TYPEDEFS(Size, SizeSuffix)                     \
 /** \ingroup matrixtypedefs */                                    \
@@ -379,7 +379,7 @@
 #undef EIGEN_MAKE_TYPEDEFS
 #undef EIGEN_MAKE_FIXED_TYPEDEFS
 
-#endif // __cplusplus>=201103L
+#endif // EIGEN_HAS_CXX11
   
 #define EIGEN_USING_ARRAY_TYPEDEFS_FOR_TYPE_AND_SIZE(TypeSuffix, SizeSuffix) \
 using Eigen::Matrix##SizeSuffix##TypeSuffix; \

Eigen/src/Core/Matrix.h

diff --git a/Eigen/src/Core/Matrix.h b/Eigen/src/Core/Matrix.h
index ea5f7da..83cffc8 100644
--- a/Eigen/src/Core/Matrix.h
+++ b/Eigen/src/Core/Matrix.h
@@ -499,7 +499,7 @@
 #undef EIGEN_MAKE_TYPEDEFS
 #undef EIGEN_MAKE_FIXED_TYPEDEFS
 
-#if __cplusplus>=201103L
+#if EIGEN_HAS_CXX11
 
 #define EIGEN_MAKE_TYPEDEFS(Size, SizeSuffix)                     \
 /** \ingroup matrixtypedefs */                                    \
@@ -531,7 +531,7 @@
 #undef EIGEN_MAKE_TYPEDEFS
 #undef EIGEN_MAKE_FIXED_TYPEDEFS
 
-#endif // __cplusplus>=201103L
+#endif // EIGEN_HAS_CXX11
 
 } // end namespace Eigen
 

test/CMakeLists.txt

diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 3dbb426..f74e22c 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -164,6 +164,7 @@
 ei_add_test(dynalloc)
 ei_add_test(nomalloc)
 ei_add_test(first_aligned)
+ei_add_test(type_alias)
 ei_add_test(nullary)
 ei_add_test(mixingtypes)
 ei_add_test(packetmath "-DEIGEN_FAST_MATH=1")

test/type_alias.cpp

diff --git a/test/type_alias.cpp b/test/type_alias.cpp
new file mode 100644
index 0000000..f9b0efc
--- /dev/null
+++ b/test/type_alias.cpp
@@ -0,0 +1,43 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 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 "main.h"
+
+EIGEN_DECLARE_TEST(type_alias)
+{
+  using namespace internal;
+
+  // To warm up, some basic checks:
+  STATIC_CHECK((is_same<MatrixXd,Matrix<double,Dynamic,Dynamic> >::value));
+  STATIC_CHECK((is_same<Matrix2f,Matrix<float,2,2> >::value));
+  STATIC_CHECK((is_same<Array33i,Array<int,3,3> >::value));
+
+#if EIGEN_HAS_CXX11
+  
+  STATIC_CHECK((is_same<MatrixX<double>,    MatrixXd>::value));
+  STATIC_CHECK((is_same<MatrixX<int>,       MatrixXi>::value));
+  STATIC_CHECK((is_same<Matrix2<int>,       Matrix2i>::value));
+  STATIC_CHECK((is_same<Matrix2X<float>,    Matrix2Xf>::value));
+  STATIC_CHECK((is_same<MatrixX4<double>,   MatrixX4d>::value));
+  STATIC_CHECK((is_same<VectorX<int>,       VectorXi>::value));
+  STATIC_CHECK((is_same<Vector2<float>,     Vector2f>::value));
+  STATIC_CHECK((is_same<RowVectorX<int>,    RowVectorXi>::value));
+  STATIC_CHECK((is_same<RowVector2<float>,  RowVector2f>::value));
+  
+  STATIC_CHECK((is_same<ArrayXX<float>,     ArrayXXf>::value));
+  STATIC_CHECK((is_same<Array33<int>,       Array33i>::value));
+  STATIC_CHECK((is_same<Array2X<float>,     Array2Xf>::value));
+  STATIC_CHECK((is_same<ArrayX4<double>,    ArrayX4d>::value));
+  STATIC_CHECK((is_same<ArrayX<double>,     ArrayXd>::value));
+  STATIC_CHECK((is_same<Array4<double>,     Array4d>::value));
+
+#else
+  std::cerr << "WARNING: c++11 type aliases not tested.\n";
+#endif
+}