feat: vectorize functions with void return type (#1969)

* Allow function/functor passed to py::vectorize to return void

* Stealing @sizmailov's test and fixing unused argument warning

* Add missing std::move()

RVO doesn't work here because function return type is different from
actual returned type

* remove extra EOL

* docs: add a few details

* chore: pre-commit autoupdate

* Remove array_iterator, array_begin, and array_end (in detail namespace)

Co-authored-by: Sergei Izmailov <sergei.a.izmailov@gmail.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>

docs/changelog.rst

@@ -98,6 +98,9 @@ See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
   ``get_type_overload`` is deprecated.
   `#2325 <https://github.com/pybind/pybind11/pull/2325>`_
 
+* Error now thrown when ``__init__`` is forgotten on subclasses.
+  `#2152 <https://github.com/pybind/pybind11/pull/2152>`_
+
 * `py::class_<union_type>` is now supported. Note that writing to one data
   member of the union and reading another (type punning) is UB in C++. Thus
   pybind11-bound enums should never be used for such conversion.
@@ -109,9 +112,6 @@ Smaller or developer focused features:
 
 .. _pybind11-mkdoc: https://github.com/pybind/pybind11-mkdoc
 
-* Error now thrown when ``__init__`` is forgotten on subclasses.
-  `#2152 <https://github.com/pybind/pybind11/pull/2152>`_
-
 * If ``__eq__`` defined but not ``__hash__``, ``__hash__`` is now set to
   ``None``.
   `#2291 <https://github.com/pybind/pybind11/pull/2291>`_
@@ -122,9 +122,6 @@ Smaller or developer focused features:
 * Throw if conversion to ``str`` fails.
   `#2477 <https://github.com/pybind/pybind11/pull/2477>`_
 
-* Added missing signature for ``py::array``.
-  `#2363 <https://github.com/pybind/pybind11/pull/2363>`_
-
 * Pointer to ``std::tuple`` & ``std::pair`` supported in cast.
   `#2334 <https://github.com/pybind/pybind11/pull/2334>`_
 
@@ -132,7 +129,13 @@ Smaller or developer focused features:
   argument type.
   `#2293 <https://github.com/pybind/pybind11/pull/2293>`_
 
-* Bugfixes related to more extensive testing
+* Added missing signature for ``py::array``.
+  `#2363 <https://github.com/pybind/pybind11/pull/2363>`_
+
+* ``py::vectorize`` is now supported on functions that return void.
+  `#1969 <https://github.com/pybind/pybind11/pull/1969>`_
+
+* Bugfixes related to more extensive testing.
   `#2321 <https://github.com/pybind/pybind11/pull/2321>`_
 
 * Bug in timezone issue in Eastern hemisphere midnight fixed.

include/pybind11/numpy.h

@@ -1274,19 +1274,6 @@ private:
 
 #endif // __CLION_IDE__
 
-template  <class T>
-using array_iterator = typename std::add_pointer<T>::type;
-
-template <class T>
-array_iterator<T> array_begin(const buffer_info& buffer) {
-    return array_iterator<T>(reinterpret_cast<T*>(buffer.ptr));
-}
-
-template <class T>
-array_iterator<T> array_end(const buffer_info& buffer) {
-    return array_iterator<T>(reinterpret_cast<T*>(buffer.ptr) + buffer.size);
-}
-
 class common_iterator {
 public:
     using container_type = std::vector<ssize_t>;
@@ -1486,6 +1473,56 @@ struct vectorize_arg {
     using type = conditional_t<vectorize, array_t<remove_cv_t<call_type>, array::forcecast>, T>;
 };
 
+
+// py::vectorize when a return type is present
+template <typename Func, typename Return, typename... Args>
+struct vectorize_returned_array {
+    using Type = array_t<Return>;
+
+    static Type create(broadcast_trivial trivial, const std::vector<ssize_t> &shape) {
+        if (trivial == broadcast_trivial::f_trivial)
+            return array_t<Return, array::f_style>(shape);
+        else
+            return array_t<Return>(shape);
+    }
+
+    static Return *mutable_data(Type &array) {
+        return array.mutable_data();
+    }
+
+    static Return call(Func &f, Args &... args) {
+        return f(args...);
+    }
+
+    static void call(Return *out, size_t i, Func &f, Args &... args) {
+        out[i] = f(args...);
+    }
+};
+
+// py::vectorize when a return type is not present
+template <typename Func, typename... Args>
+struct vectorize_returned_array<Func, void, Args...> {
+    using Type = none;
+
+    static Type create(broadcast_trivial, const std::vector<ssize_t> &) {
+        return none();
+    }
+
+    static void *mutable_data(Type &) {
+        return nullptr;
+    }
+
+    static detail::void_type call(Func &f, Args &... args) {
+        f(args...);
+        return {};
+    }
+
+    static void call(void *, size_t, Func &f, Args &... args) {
+        f(args...);
+    }
+};
+
+
 template <typename Func, typename Return, typename... Args>
 struct vectorize_helper {
 
@@ -1520,6 +1557,8 @@ private:
     using arg_call_types = std::tuple<typename vectorize_arg<Args>::call_type...>;
     template <size_t Index> using param_n_t = typename std::tuple_element<Index, arg_call_types>::type;
 
+    using returned_array = vectorize_returned_array<Func, Return, Args...>;
+
     // Runs a vectorized function given arguments tuple and three index sequences:
     //     - Index is the full set of 0 ... (N-1) argument indices;
     //     - VIndex is the subset of argument indices with vectorized parameters, letting us access
@@ -1551,20 +1590,19 @@ private:
         // not wrapped in an array).
         if (size == 1 && ndim == 0) {
             PYBIND11_EXPAND_SIDE_EFFECTS(params[VIndex] = buffers[BIndex].ptr);
-            return cast(f(*reinterpret_cast<param_n_t<Index> *>(params[Index])...));
+            return cast(returned_array::call(f, *reinterpret_cast<param_n_t<Index> *>(params[Index])...));
         }
 
-        array_t<Return> result;
-        if (trivial == broadcast_trivial::f_trivial) result = array_t<Return, array::f_style>(shape);
-        else result = array_t<Return>(shape);
+        auto result = returned_array::create(trivial, shape);
 
         if (size == 0) return std::move(result);
 
         /* Call the function */
+        auto mutable_data = returned_array::mutable_data(result);
         if (trivial == broadcast_trivial::non_trivial)
-            apply_broadcast(buffers, params, result, i_seq, vi_seq, bi_seq);
+            apply_broadcast(buffers, params, mutable_data, size, shape, i_seq, vi_seq, bi_seq);
         else
-            apply_trivial(buffers, params, result.mutable_data(), size, i_seq, vi_seq, bi_seq);
+            apply_trivial(buffers, params, mutable_data, size, i_seq, vi_seq, bi_seq);
 
         return std::move(result);
     }
@@ -1587,7 +1625,7 @@ private:
         }};
 
         for (size_t i = 0; i < size; ++i) {
-            out[i] = f(*reinterpret_cast<param_n_t<Index> *>(params[Index])...);
+            returned_array::call(out, i, f, *reinterpret_cast<param_n_t<Index> *>(params[Index])...);
             for (auto &x : vecparams) x.first += x.second;
         }
     }
@@ -1595,19 +1633,18 @@ private:
     template <size_t... Index, size_t... VIndex, size_t... BIndex>
     void apply_broadcast(std::array<buffer_info, NVectorized> &buffers,
                          std::array<void *, N> &params,
-                         array_t<Return> &output_array,
+                         Return *out,
+                         size_t size,
+                         const std::vector<ssize_t> &output_shape,
                          index_sequence<Index...>, index_sequence<VIndex...>, index_sequence<BIndex...>) {
 
-        buffer_info output = output_array.request();
-        multi_array_iterator<NVectorized> input_iter(buffers, output.shape);
+        multi_array_iterator<NVectorized> input_iter(buffers, output_shape);
 
-        for (array_iterator<Return> iter = array_begin<Return>(output), end = array_end<Return>(output);
-             iter != end;
-             ++iter, ++input_iter) {
+        for (size_t i = 0; i < size; ++i, ++input_iter) {
             PYBIND11_EXPAND_SIDE_EFFECTS((
                 params[VIndex] = input_iter.template data<BIndex>()
             ));
-            *iter = f(*reinterpret_cast<param_n_t<Index> *>(std::get<Index>(params))...);
+            returned_array::call(out, i, f, *reinterpret_cast<param_n_t<Index> *>(std::get<Index>(params))...);
         }
     }
 };

tests/test_numpy_vectorize.cpp

@@ -50,7 +50,9 @@ TEST_SUBMODULE(numpy_vectorize, m) {
         NonPODClass(int v) : value{v} {}
         int value;
     };
-    py::class_<NonPODClass>(m, "NonPODClass").def(py::init<int>());
+    py::class_<NonPODClass>(m, "NonPODClass")
+        .def(py::init<int>())
+        .def_readwrite("value", &NonPODClass::value);
     m.def("vec_passthrough", py::vectorize(
         [](double *a, double b, py::array_t<double> c, const int &d, int &e, NonPODClass f, const double g) {
             return *a + b + c.at(0) + d + e + f.value + g;
@@ -86,4 +88,6 @@ TEST_SUBMODULE(numpy_vectorize, m) {
         std::array<py::buffer_info, 3> buffers {{ arg1.request(), arg2.request(), arg3.request() }};
         return py::detail::broadcast(buffers, ndim, shape);
     });
+
+    m.def("add_to", py::vectorize([](NonPODClass& x, int a) { x.value += a; }));
 }

tests/test_numpy_vectorize.py

@@ -192,3 +192,14 @@ def test_array_collapse():
     z = m.vectorized_func(1, [[[2]]], 3)
     assert isinstance(z, np.ndarray)
     assert z.shape == (1, 1, 1)
+
+
+def test_vectorized_noreturn():
+    x = m.NonPODClass(0)
+    assert x.value == 0
+    m.add_to(x, [1, 2, 3, 4])
+    assert x.value == 10
+    m.add_to(x, 1)
+    assert x.value == 11
+    m.add_to(x, [[1, 1], [2, 3]])
+    assert x.value == 18