Zengtudor/pybind11
1
0
Fork 0
mirror of https://github.com/pybind/pybind11.git synced 2024-11-22 05:05:11 +00:00
Code Issues Packages Projects Releases Wiki Activity

Fail static_assert when trying to reference non-referencable types

Browse Source 
The previous commit to address #392 triggers a compiler warning about
returning a reference to a local variable, which is *not* a false alarm:
the following:

    py::cast<int &>(o)

(which happens internally in an overload declaration) really is
returning a reference to a local, because the cast operators for the
type_caster for numeric types returns a reference to its own member.

This commit adds a static_assert to make that a compilation failure
rather than returning a reference into about-to-be-freed memory.

Incidentally, this is also a fix for #219, which is exactly the same
issue: we can't reference numeric primitives that are cast from
wrappers around python numeric types.
This commit is contained in:
Jason Rhinelander 2016-09-07 13:38:32 -04:00
parent 56f717756b
commit c03db9bad9
3 changed files with 20 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/pybind11/cast.h
View File

@ -855,10 +855,22 @@ template <typename T> struct move_if_unreferenced<T, typename std::enable_if<
>::type> : std::true_type {};
template <typename T> using move_never = std::integral_constant<bool, !move_always<T>::value && !move_if_unreferenced<T>::value>;
// Detect whether returning a `type` from a cast on type's type_caster is going to result in a
// reference or pointer to a local variable of the type_caster. Basically, only
// non-reference/pointer `type`s and reference/pointers from a type_caster_generic are safe;
// everything else returns a reference/pointer to a local variable.
template <typename type> using cast_is_temporary_value_reference = bool_constant<
(std::is_reference<type>::value || std::is_pointer<type>::value) &&
!std::is_base_of<type_caster_generic, make_caster<type>>::value
>;
NAMESPACE_END(detail)
template <typename T> T cast(const handle &handle) {
using type_caster = detail::make_caster<T>;
static_assert(!detail::cast_is_temporary_value_reference<T>::value,
"Unable to cast type to reference: value is local to type caster");
type_caster conv;
if (!conv.load(handle, true)) {
#if defined(NDEBUG)

7
tests/test_issues.cpp
View File

@ -208,7 +208,9 @@ void init_issues(py::module &m) {
public:
using OverrideTest::OverrideTest;
int int_value() override { PYBIND11_OVERLOAD(int, OverrideTest, int_value); }
int &int_ref() override { PYBIND11_OVERLOAD(int &, OverrideTest, int_ref); }
// Not allowed (uncommenting should hit a static_assert failure): we can't get a reference
// to a python numeric value, since we only copy values in the numeric type caster:
// int &int_ref() override { PYBIND11_OVERLOAD(int &, OverrideTest, int_ref); }
A A_value() override { PYBIND11_OVERLOAD(A, OverrideTest, A_value); }
A &A_ref() override { PYBIND11_OVERLOAD(A &, OverrideTest, A_ref); }
};
@ -217,9 +219,10 @@ void init_issues(py::module &m) {
py::class_<OverrideTest, PyOverrideTest>(m2, "OverrideTest")
.def(py::init<int>())
.def("int_value", &OverrideTest::int_value)
.def("int_ref", &OverrideTest::int_ref)
// .def("int_ref", &OverrideTest::int_ref)
.def("A_value", &OverrideTest::A_value)
.def("A_ref", &OverrideTest::A_ref);
}
// MSVC workaround: trying to use a lambda here crashes MSCV

5
tests/test_issues.py
View File

@ -171,9 +171,10 @@ def test_override_ref():
from pybind11_tests.issues import OverrideTest
o = OverrideTest(42)
i = o.int_ref()
# Not allowed (see associated .cpp comment)
#i = o.int_ref()
#assert o.int_ref() == 42
assert o.int_value() == 42
assert o.int_ref() == 42
assert o.A_value().value == 99
a = o.A_ref()