From 96aeffb0131e6e0df44bd376b3db693392cdf9c7 Mon Sep 17 00:00:00 2001
From: Rasmus Munk Larsen <rmlarsen@google.com>
Date: Wed, 17 Nov 2021 18:16:04 -0800
Subject: [PATCH] Make the new TensorIO implementation work with TensorMap with
 const elements.

---
 unsupported/Eigen/CXX11/src/Tensor/TensorIO.h |  4 ++--
 unsupported/test/cxx11_tensor_io.cpp          | 13 +++++++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorIO.h b/unsupported/Eigen/CXX11/src/Tensor/TensorIO.h
index 3e95f95fa..b958f6abb 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorIO.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorIO.h
@@ -186,7 +186,7 @@ namespace internal {
 template <typename Tensor, std::size_t rank>
 struct TensorPrinter {
   static void run(std::ostream& s, const Tensor& _t, const TensorIOFormat& fmt) {
-    typedef typename Tensor::Scalar Scalar;
+    typedef typename internal::remove_const<typename Tensor::Scalar>::type Scalar;
     typedef typename Tensor::Index Index;
     static const int layout = Tensor::Layout;
     // backwards compatibility case: print tensor after reshaping to matrix of size dim(0) x
@@ -195,7 +195,7 @@ struct TensorPrinter {
       const Index total_size = internal::array_prod(_t.dimensions());
       if (total_size > 0) {
         const Index first_dim = Eigen::internal::array_get<0>(_t.dimensions());
-        Map<const Array<Scalar, Dynamic, Dynamic, layout> > matrix(const_cast<Scalar*>(_t.data()), first_dim,
+        Map<const Array<Scalar, Dynamic, Dynamic, layout> > matrix(_t.data(), first_dim,
                                                                    total_size / first_dim);
         s << matrix;
         return;
diff --git a/unsupported/test/cxx11_tensor_io.cpp b/unsupported/test/cxx11_tensor_io.cpp
index 34fcbc3ff..c0ea2a101 100644
--- a/unsupported/test/cxx11_tensor_io.cpp
+++ b/unsupported/test/cxx11_tensor_io.cpp
@@ -90,6 +90,16 @@ void test_tensor_ostream() {
   test_tensor_ostream_impl<Scalar, rank, Layout>::run();
 }
 
+void test_const_tensor_ostream() {
+  Eigen::Tensor<float, 0> t;
+  t.setValues(1);
+  const Eigen::TensorMap<Eigen::Tensor<const float, 0, Eigen::RowMajor>, Eigen::Unaligned> t_const(
+      t.data(), Eigen::DSizes<Eigen::DenseIndex, 0>{});
+  std::ostringstream os;
+  os << t_const.format(Eigen::TensorIOFormat::Plain());
+  VERIFY(os.str() == "1");
+}
+
 EIGEN_DECLARE_TEST(cxx11_tensor_io) {
   CALL_SUBTEST((test_tensor_ostream<float, 0, Eigen::ColMajor>()));
   CALL_SUBTEST((test_tensor_ostream<float, 1, Eigen::ColMajor>()));
@@ -126,4 +136,7 @@ EIGEN_DECLARE_TEST(cxx11_tensor_io) {
 
   CALL_SUBTEST((test_tensor_ostream<std::complex<double>, 2, Eigen::ColMajor>()));
   CALL_SUBTEST((test_tensor_ostream<std::complex<float>, 2, Eigen::ColMajor>()));
+
+  // Test printing TensorMap with const elements.
+  CALL_SUBTEST((test_const_tensor_ostream()));
 }