Assert that XTensor objects are row-major.

Easy serializes XTensor objects by obtaining a pointer to the first
element, and then using `write_raw`. Same for reading using `read_raw`.

Therefore, it only supports (a subset of) row-major arrays. This commit
as a runtime check.

include/highfive/h5easy_bits/H5Easy_xtensor.hpp

@@ -20,6 +20,12 @@ namespace detail {
 
 template <typename T>
 struct io_impl<T, typename std::enable_if<xt::is_xexpression<T>::value>::type> {
+    inline static void assert_row_major(const File& file, const std::string& path, const T& data) {
+        if (data.layout() != xt::layout_type::row_major) {
+            throw detail::error(file, path, "Only row-major XTensor object are supported.");
+        }
+    }
+
     inline static std::vector<size_t> shape(const T& data) {
         return std::vector<size_t>(data.shape().cbegin(), data.shape().cend());
     }
@@ -28,6 +34,7 @@ struct io_impl<T, typename std::enable_if<xt::is_xexpression<T>::value>::type> {
                                const std::string& path,
                                const T& data,
                                const DumpOptions& options) {
+        assert_row_major(file, path, data);
         using value_type = typename std::decay_t<T>::value_type;
         DataSet dataset = initDataset<value_type>(file, path, shape(data), options);
         dataset.write_raw(data.data());
@@ -44,6 +51,7 @@ struct io_impl<T, typename std::enable_if<xt::is_xexpression<T>::value>::type> {
         DataSet dataset = file.getDataSet(path);
         std::vector<size_t> dims = dataset.getDimensions();
         T data = T::from_shape(dims);
+        assert_row_major(file, path, data);
         dataset.read_raw(data.data());
         return data;
     }
@@ -53,6 +61,7 @@ struct io_impl<T, typename std::enable_if<xt::is_xexpression<T>::value>::type> {
                                           const std::string& key,
                                           const T& data,
                                           const DumpOptions& options) {
+        assert_row_major(file, path, data);
         using value_type = typename std::decay_t<T>::value_type;
         Attribute attribute = initAttribute<value_type>(file, path, key, shape(data), options);
         attribute.write_raw(data.data());
@@ -73,6 +82,7 @@ struct io_impl<T, typename std::enable_if<xt::is_xexpression<T>::value>::type> {
         DataSpace dataspace = attribute.getSpace();
         std::vector<size_t> dims = dataspace.getDimensions();
         T data = T::from_shape(dims);
+        assert_row_major(file, path, data);
         attribute.read_raw(data.data());
         return data;
     }

tests/unit/tests_high_five_easy.cpp

@@ -243,6 +243,44 @@ TEST_CASE("H5Easy_xtensor") {
     CHECK(xt::all(xt::equal(B, B_r)));
 }
 
+TEST_CASE("H5Easy_xtensor_column_major") {
+    H5Easy::File file("h5easy_xtensor_colum_major.h5", H5Easy::File::Overwrite);
+
+    using column_major_t = xt::xtensor<double, 2, xt::layout_type::column_major>;
+
+    xt::xtensor<double, 2> A = 100. * xt::random::randn<double>({20, 5});
+
+    H5Easy::dump(file, "/path/to/A", A);
+
+    SECTION("Write column major") {
+        column_major_t B = A;
+        REQUIRE_THROWS(H5Easy::dump(file, "path/to/B", B));
+    }
+
+    SECTION("Read column major") {
+        REQUIRE_THROWS(H5Easy::load<column_major_t>(file, "/path/to/A"));
+    }
+}
+
+TEST_CASE("H5Easy_xarray_column_major") {
+    H5Easy::File file("h5easy_xarray_colum_major.h5", H5Easy::File::Overwrite);
+
+    using column_major_t = xt::xarray<double, xt::layout_type::column_major>;
+
+    xt::xarray<double> A = 100. * xt::random::randn<double>({20, 5});
+
+    H5Easy::dump(file, "/path/to/A", A);
+
+    SECTION("Write column major") {
+        column_major_t B = A;
+        REQUIRE_THROWS(H5Easy::dump(file, "path/to/B", B));
+    }
+
+    SECTION("Read column major") {
+        REQUIRE_THROWS(H5Easy::load<column_major_t>(file, "/path/to/A"));
+    }
+}
+
 TEST_CASE("H5Easy_xarray") {
     H5Easy::File file("h5easy_xarray.h5", H5Easy::File::Overwrite);