Add `SimpleArray::as_span()` and `as_mdspan<N>()` by yungyuc · Pull Request #777 · solvcon/modmesh

yungyuc · 2026-05-13T14:05:19Z

Expose C++23 view types over the contiguous buffer:

as_span() returns std::span<value_type> over the contiguous body.
as_mdspan<N>() returns std::mdspan<value_type, std::dextents<size_t, N>> built from shape(). Ghost indices are not subtracted. The view spans the full underlying storage.

Add gtests/test_nopython_mdspan.cpp covering 1D-4D shapes, ghost arrays for each rank, and the as_span() linear view.

This is for issue #771 .

yungyuc · 2026-05-13T14:05:52Z

    template <typename... Args>
    value_type * vptr(Args... args) { return m_body + buffer_offset(m_stride, args...); }

+    std::span<value_type> as_span() { return std::span<value_type>(data(), size()); }


Linear view.

yungyuc · 2026-05-13T14:06:00Z

+    std::span<value_type const> as_span() const { return std::span<value_type const>(data(), size()); }
+
+    template <size_t N>
+    std::mdspan<value_type, std::dextents<size_t, N>> as_mdspan()


Multi-dimensional view.

yungyuc · 2026-05-13T14:06:11Z

+    {
+        if (ndim() != N)
+        {
+            throw std::out_of_range(


Runtime shape check.

yungyuc · 2026-05-13T14:06:29Z

+        }
+        std::array<size_t, N> exts;
+        for (size_t i = 0; i < N; ++i) { exts[i] = shape(i); }
+        return std::mdspan<value_type, std::dextents<size_t, N>>(data(), exts);


Use data(). Disregard ghost information.

yungyuc · 2026-05-13T14:10:05Z

+#error "Python.h should not be included."
+#endif
+
+TEST(SimpleArray, mdspan_1d)


1D test. Uninteresting.

yungyuc · 2026-05-13T14:10:15Z

+    EXPECT_EQ(sp[3], 99.0);
+}
+
+TEST(SimpleArray, mdspan_1d_const)


yungyuc · 2026-05-13T14:10:21Z

+    for (size_t i = 0; i < 6; ++i) { EXPECT_EQ(sp[i], 5.0); }
+}
+
+TEST(SimpleArray, mdspan_1d_ghost)


Test with ghost.

yungyuc · 2026-05-13T14:10:39Z

+    {
+        for (size_t j = 0; j < 4; ++j)
+        {
+            arr(i, j) = static_cast<double>(i * 4 + j);


2D test. A little bit interesting.

yungyuc · 2026-05-13T14:10:48Z

+        }
+    }
+
+    // Linear view over the C-contiguous buffer; sp[i*4+j] == arr(i, j).


Linear view for 2D buffer.

yungyuc · 2026-05-13T14:11:01Z

+    for (size_t k = 0; k < sp.size(); ++k) { EXPECT_EQ(sp[k], arr.data(k)); }
+}
+
+TEST(SimpleArray, mdspan_3d)


So on and so forth for 3D and 4D.

yungyuc · 2026-05-14T14:36:21Z

        sudo ln -fs "$(which clang-tidy-22)" "/usr/local/bin/clang-tidy"

-    - name: Install and configure gcc-14
+    - name: Install and configure gcc-16


The GCC 14 and 15 with the ubuntu package did not have mdspan.

Although we may face CI error when ubuntu PPA dies again, it seems that GCC 16 is necessary.

yungyuc · 2026-05-14T14:37:09Z

@tigercosmos @ExplorerRay @ThreeMonth03 please help take a look.

ExplorerRay

LGTM.

ThreeMonth03 · 2026-05-14T17:05:38Z

+                std::format("SimpleArray::as_mdspan: rank {} does not match ndim() {}", N, ndim()));
+        }
+        std::array<size_t, N> exts;
+        for (size_t i = 0; i < N; ++i) { exts[i] = shape(i); }


It may be checked whether SimpleArray is contiguous. The size of shape may not equal to the size of data().

Good catch. Added above.

Expose C++23 view types over the contiguous buffer: - `as_span()` returns `std::span<value_type>` over the contiguous body. - `as_mdspan<N>()` returns `std::mdspan<value_type, std::dextents<size_t, N>>` built from `shape()`. Ghost indices are not subtracted. The view spans the full underlying storage. Add `gtests/test_nopython_mdspan.cpp` covering 1D-4D shapes, ghost arrays for each rank, and the `as_span()` linear view.

gcc-14 and gcc-15 from ppa:ubuntu-toolchain-r/test does not ship <mdspan> in libstdc++-15-dev.

Both views assume linear row-major storage of prod(shape) elements starting at data(). Reject a non-C-contiguous array (e.g., padded or strided view) with std::runtime_error. Add `SimpleArray.mdspan_non_contiguous` to cover the new guard.

yungyuc · 2026-05-14T23:29:56Z

+                std::format("SimpleArray::as_mdspan: rank {} does not match ndim() {}", N, ndim()));
+        }
+        std::array<size_t, N> exts;
+        for (size_t i = 0; i < N; ++i) { exts[i] = shape(i); }


Good catch. Added above.

yungyuc · 2026-05-14T23:30:13Z

+            throw std::out_of_range(
+                std::format("SimpleArray::as_mdspan: rank {} does not match ndim() {}", N, ndim()));
+        }
+        if (!is_c_contiguous())


Throw if the buffer is not C-contiguous.

It looks great now.

yungyuc · 2026-05-14T23:30:29Z

+    EXPECT_THROW(arr.as_mdspan<3>(), std::out_of_range);
+}
+
+TEST(SimpleArray, mdspan_non_contiguous)


Test for non-C-contiguous.

yungyuc · 2026-05-14T23:31:07Z

Rebased to latest master.

ThreeMonth03

LGTM. We may consider the non cotiguous case by another pull request.

ThreeMonth03 · 2026-05-15T03:04:31Z

+            throw std::out_of_range(
+                std::format("SimpleArray::as_mdspan: rank {} does not match ndim() {}", N, ndim()));
+        }
+        if (!is_c_contiguous())


It looks great now.

yungyuc · 2026-05-15T03:09:07Z

One of the linter runs keeps timeout. It should be false alarm and I'll merge.

yungyuc · 2026-05-15T04:02:54Z

LGTM. We may consider the non cotiguous case by another pull request.

Tracking noncontiguous support in issue #784 .

yungyuc self-assigned this May 13, 2026

yungyuc added the array Multi-dimensional array implementation label May 13, 2026

yungyuc force-pushed the feat/mdspan branch from 7558e65 to c4478c4 Compare May 13, 2026 14:09

yungyuc commented May 13, 2026

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yungyuc force-pushed the feat/mdspan branch from c4478c4 to 2022bc6 Compare May 14, 2026 14:15

yungyuc commented May 14, 2026

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yungyuc marked this pull request as ready for review May 14, 2026 14:36

yungyuc requested review from ExplorerRay, ThreeMonth03 and chestercheng May 14, 2026 14:36

yungyuc requested review from KHLee529 and tigercosmos May 14, 2026 14:37

ExplorerRay approved these changes May 14, 2026

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ThreeMonth03 reviewed May 14, 2026

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yungyuc added 3 commits May 15, 2026 07:25

Upgrade Ubuntu CI gcc-14 to gcc-16 for <mdspan>

5672eb0

gcc-14 and gcc-15 from ppa:ubuntu-toolchain-r/test does not ship <mdspan> in libstdc++-15-dev.

yungyuc force-pushed the feat/mdspan branch from 2022bc6 to 324c472 Compare May 14, 2026 23:29

yungyuc commented May 14, 2026

View reviewed changes

ThreeMonth03 approved these changes May 15, 2026

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yungyuc merged commit bf36b16 into solvcon:master May 15, 2026
22 of 26 checks passed

yungyuc deleted the feat/mdspan branch May 15, 2026 03:09

yungyuc linked an issue May 15, 2026 that may be closed by this pull request

SimpleArray to support std::mdspan #771

Closed

yungyuc mentioned this pull request May 15, 2026

Support non-contiguous buffers in SimpleArray::as_span/as_mdspan() #784

Open

yungyuc mentioned this pull request May 15, 2026

SimpleArray to support std::mdspan #771

Closed

yungyuc added this to tensor operations May 15, 2026

github-project-automation Bot moved this from Todo to Done in tensor operations May 15, 2026

github-project-automation Bot moved this to Todo in tensor operations May 15, 2026

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