python: add a caster for Containers::Optional.

doc/python/pages/changelog.rst

@@ -55,6 +55,9 @@ Changelog
 -   The Homebrew package now uses `std_cmake_args` instead of hardcoded build
     type and install prefix, which resolves certain build issues (see
     :gh:`mosra/homebrew-magnum#6`)
+-   Added a caster for :dox:`Containers::Optional`, allowing it to be used
+    directly in function signatures and showing up on the Python side as either
+    :py:`None` or the actual value
 
 `2020.06`_
 ==========

src/Corrade/Containers/CMakeLists.txt

@@ -25,6 +25,7 @@
 
 if(WITH_PYTHON)
     set(CorradeContainersPython_HEADERS
+        OptionalPythonBindings.h
         PythonBindings.h
         StridedArrayViewPythonBindings.h)
 

src/Corrade/Containers/OptionalPythonBindings.h

@@ -0,0 +1,62 @@
+#ifndef Corrade_Containers_OptionalPythonBindings_h
+#define Corrade_Containers_OptionalPythonBindings_h
+/*
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019,
+                2020, 2021 Vladimír Vondruš <mosra@centrum.cz>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+#include <pybind11/pybind11.h>
+#include <Corrade/Containers/Optional.h>
+
+namespace pybind11 { namespace detail {
+
+/* pybind11/stl.h has optional_caster for this, but that relies on a value_type
+   typedef that Optional doesn't have, so adapting a copy of it, also without
+   std::is_lvalue_reference<T>::value, which is not a thing here */
+template<class T> struct type_caster<Corrade::Containers::Optional<T>> {
+    using value_conv = make_caster<T>;
+
+    template<class T_> static handle cast(T_&& src, const return_value_policy policy, const handle parent) {
+        if(!src) return none{}.inc_ref();
+        return value_conv::cast(*std::forward<T_>(src), return_value_policy_override<T>::policy(policy), parent);
+    }
+
+    bool load(const handle src, bool convert) {
+        if(!src) return false;
+
+        /* default-constructed value is already empty */
+        if(src.is_none()) return true;
+
+        value_conv inner_caster;
+        if(!inner_caster.load(src, convert)) return false;
+
+        value.emplace(cast_op<T&&>(std::move(inner_caster)));
+        return true;
+    }
+
+    PYBIND11_TYPE_CASTER(Corrade::Containers::Optional<T>, _("Optional[") + value_conv::name + _("]"));
+};
+
+}}
+
+#endif

src/python/corrade/test/CMakeLists.txt

@@ -23,9 +23,11 @@
 #   DEALINGS IN THE SOFTWARE.
 #
 
-pybind11_add_module(test_stridedarrayview ${pybind11_add_module_SYSTEM} test_stridedarrayview.cpp)
-target_include_directories(test_stridedarrayview PRIVATE ${PROJECT_SOURCE_DIR}/src)
-target_link_libraries(test_stridedarrayview PRIVATE Corrade::Containers)
-set_target_properties(test_stridedarrayview PROPERTIES
-    FOLDER "python"
-    LIBRARY_OUTPUT_DIRECTORY ${output_dir})
+foreach(_test optional stridedarrayview)
+    pybind11_add_module(test_${_test} ${pybind11_add_module_SYSTEM} test_${_test}.cpp)
+    target_include_directories(test_${_test} PRIVATE ${PROJECT_SOURCE_DIR}/src)
+    target_link_libraries(test_${_test} PRIVATE Corrade::Containers)
+    set_target_properties(test_${_test} PROPERTIES
+        FOLDER "python"
+        LIBRARY_OUTPUT_DIRECTORY ${output_dir})
+endforeach()

src/python/corrade/test/test_containers.py

@@ -29,6 +29,7 @@ import unittest
 
 from corrade import containers
 import test_stridedarrayview
+import test_optional
 
 class ArrayView(unittest.TestCase):
     def test_init(self):
@@ -900,3 +901,16 @@ class StridedArrayViewCustomType(unittest.TestCase):
 
     # mutable_vector3d and mutable_long_float tested in test_containers_numpy
     # as memoryview can't handle their types
+
+class TestOptional(unittest.TestCase):
+    def test_simple(self):
+        self.assertIsNone(test_optional.simple_type(False))
+        self.assertEqual(test_optional.simple_type(True), 5)
+        self.assertEqual(test_optional.acquire_simple_type(None), -1)
+        self.assertEqual(test_optional.acquire_simple_type(15), 15)
+
+    def test_nested(self):
+        self.assertIsNone(test_optional.nested_type(False))
+        self.assertEqual(test_optional.nested_type(True).a, 15)
+        self.assertEqual(test_optional.acquire_nested_type(None), -1)
+        self.assertEqual(test_optional.acquire_nested_type(test_optional.Foo(25)), 25)

src/python/corrade/test/test_optional.cpp

@@ -0,0 +1,75 @@
+/*
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019,
+                2020, 2021 Vladimír Vondruš <mosra@centrum.cz>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+#include <pybind11/pybind11.h>
+
+#include "../bootstrap.h" /* for module / _module alias */
+
+#include "Corrade/Containers/OptionalPythonBindings.h"
+
+using namespace Corrade;
+namespace py = pybind11;
+
+namespace {
+
+struct Foo {
+    Foo(int a): a{a} {}
+    int a;
+};
+
+Containers::Optional<int> simpleType(bool set) {
+    return set ? Containers::optional(5) : Containers::NullOpt;
+}
+
+Containers::Optional<Foo> nestedType(bool set) {
+    return set ? Containers::optional(Foo{15}) : Containers::NullOpt;
+}
+
+int acquireSimpleType(Containers::Optional<int> value) {
+    return value ? *value : -1;
+}
+
+int acquireNestedType(Containers::Optional<Foo> value) {
+    return value ? value->a : -1;
+}
+
+}
+
+/* TODO: remove declaration when https://github.com/pybind/pybind11/pull/1863
+   is released */
+extern "C" PYBIND11_EXPORT PyObject* PyInit_test_optional();
+PYBIND11_MODULE(test_optional, m) {
+    py::module_::import("corrade.containers");
+
+    py::class_<Foo>{m, "Foo"}
+        .def(py::init<int>())
+        .def_readwrite("a", &Foo::a);
+
+    m.def("simple_type", simpleType);
+    m.def("nested_type", nestedType);
+
+    m.def("acquire_simple_type", acquireSimpleType);
+    m.def("acquire_nested_type", acquireNestedType);
+}