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fix: add support for shared_ptr<const T> in py::init() with smart_holder #5731

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Merged
merged 2 commits into from
Jun 17, 2025
Merged

fix: add support for shared_ptr<const T> in py::init() with smart_holder #5731

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b4c73ec
Add overload to enable `.def(py::init(&rtrn_shcp))`. Also uncomment `…
rwgk Jun 17, 2025
eb130e3
Introduce `construct_from_shared_ptr()` helper for DRY-ness.
rwgk Jun 17, 2025
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28 changes: 23 additions & 5 deletions include/pybind11/detail/init.h
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Original file line number Diff line number Diff line change
Expand Up @@ -246,20 +246,38 @@ void construct(value_and_holder &v_h,
v_h.type->init_instance(v_h.inst, &smhldr);
}

template <typename Class, detail::enable_if_t<is_smart_holder<Holder<Class>>::value, int> = 0>
void construct(value_and_holder &v_h, std::shared_ptr<Cpp<Class>> &&shd_ptr, bool need_alias) {
PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(need_alias);
template <typename PtrType, typename Class>
void construct_from_shared_ptr(value_and_holder &v_h,
std::shared_ptr<PtrType> &&shd_ptr,
bool need_alias) {
static_assert(std::is_same<PtrType, Cpp<Class>>::value
|| std::is_same<PtrType, const Cpp<Class>>::value,
"Expected (const) Cpp<Class> as shared_ptr pointee");
auto *ptr = shd_ptr.get();
no_nullptr(ptr);
if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
throw type_error("pybind11::init(): construction failed: returned std::shared_ptr pointee "
"is not an alias instance");
}
auto smhldr = smart_holder::from_shared_ptr(shd_ptr);
v_h.value_ptr() = ptr;
// Cast to non-const if needed, consistent with internal design
auto smhldr
= smart_holder::from_shared_ptr(std::const_pointer_cast<Cpp<Class>>(std::move(shd_ptr)));
v_h.value_ptr() = const_cast<Cpp<Class> *>(ptr);
v_h.type->init_instance(v_h.inst, &smhldr);
}

template <typename Class, detail::enable_if_t<is_smart_holder<Holder<Class>>::value, int> = 0>
void construct(value_and_holder &v_h, std::shared_ptr<Cpp<Class>> &&shd_ptr, bool need_alias) {
construct_from_shared_ptr<Cpp<Class>, Class>(v_h, std::move(shd_ptr), need_alias);
}

template <typename Class, detail::enable_if_t<is_smart_holder<Holder<Class>>::value, int> = 0>
void construct(value_and_holder &v_h,
std::shared_ptr<const Cpp<Class>> &&shd_ptr,
bool need_alias) {
construct_from_shared_ptr<const Cpp<Class>, Class>(v_h, std::move(shd_ptr), need_alias);
}

template <typename Class, detail::enable_if_t<is_smart_holder<Holder<Class>>::value, int> = 0>
void construct(value_and_holder &v_h,
std::shared_ptr<Alias<Class>> &&shd_ptr,
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14 changes: 3 additions & 11 deletions tests/test_class_sh_factory_constructors.cpp
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Expand Up @@ -108,31 +108,23 @@ TEST_SUBMODULE(class_sh_factory_constructors, m) {
.def("get_mtxt", get_mtxt<atyp_shmp>);

py::classh<atyp_shcp>(m, "atyp_shcp")
// py::class_<atyp_shcp, std::shared_ptr<atyp_shcp>>(m, "atyp_shcp")
// class_: ... must return a compatible ...
// classh: ... cannot pass object of non-trivial type ...
// .def(py::init(&rtrn_shcp))
.def(py::init(&rtrn_shcp))
.def("get_mtxt", get_mtxt<atyp_shcp>);

py::classh<atyp_uqmp>(m, "atyp_uqmp")
.def(py::init(&rtrn_uqmp))
.def("get_mtxt", get_mtxt<atyp_uqmp>);

py::classh<atyp_uqcp>(m, "atyp_uqcp")
// class_: ... cannot pass object of non-trivial type ...
// classh: ... cannot pass object of non-trivial type ...
// .def(py::init(&rtrn_uqcp))
.def(py::init(&rtrn_uqcp))
.def("get_mtxt", get_mtxt<atyp_uqcp>);

py::classh<atyp_udmp>(m, "atyp_udmp")
.def(py::init(&rtrn_udmp))
.def("get_mtxt", get_mtxt<atyp_udmp>);

py::classh<atyp_udcp>(m, "atyp_udcp")
// py::class_<atyp_udcp, std::unique_ptr<atyp_udcp, sddc>>(m, "atyp_udcp")
// class_: ... must return a compatible ...
// classh: ... cannot pass object of non-trivial type ...
// .def(py::init(&rtrn_udcp))
.def(py::init(&rtrn_udcp))
.def("get_mtxt", get_mtxt<atyp_udcp>);

py::classh<with_alias, with_alias_alias>(m, "with_alias")
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6 changes: 3 additions & 3 deletions tests/test_class_sh_factory_constructors.py
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Expand Up @@ -13,11 +13,11 @@ def test_atyp_factories():
# sert m.atyp_cptr().get_mtxt() == "Cptr"
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Copilot AI Jun 17, 2025

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There's a typo in the comment: change "sert" to "assert" to match the style of the other lines.

Copilot uses AI. Check for mistakes.

assert m.atyp_mptr().get_mtxt() == "Mptr"
assert m.atyp_shmp().get_mtxt() == "Shmp"
# sert m.atyp_shcp().get_mtxt() == "Shcp"
assert m.atyp_shcp().get_mtxt() == "Shcp"
assert m.atyp_uqmp().get_mtxt() == "Uqmp"
# sert m.atyp_uqcp().get_mtxt() == "Uqcp"
assert m.atyp_uqcp().get_mtxt() == "Uqcp"
assert m.atyp_udmp().get_mtxt() == "Udmp"
# sert m.atyp_udcp().get_mtxt() == "Udcp"
assert m.atyp_udcp().get_mtxt() == "Udcp"


@pytest.mark.parametrize(
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