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Fix assertion failure for unions (#1685) (#1709)

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In def_readonly and def_readwrite, there is an assertion that the member comes
from the class or a base class:

    static_assert(std::is_base_of<C, type>::value, "...");

However, if C and type are the same type, is_base_of will still only be true
if they are the same _non-union_ type.  This means we can't define accessors
for the members of a union type because of this assertion.

Update the assertion to test

    std::is_same<C, type>::value || std::is_base_of<C, type>::value

which will allow union types, or members of base classes.

Also add a basic unit test for accessing unions.
This commit is contained in:
Roland Dreier 2019-06-11 13:25:12 -07:00 committed by Wenzel Jakob
parent 0071a3feb0
commit 1aa8dd1745
4 changed files with 33 additions and 2 deletions
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4
include/pybind11/pybind11.h
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@ -1185,7 +1185,7 @@ public:
template <typename C, typename D, typename... Extra>
class_ &def_readwrite(const char *name, D C::*pm, const Extra&... extra) {
static_assert(std::is_base_of<C, type>::value, "def_readwrite() requires a class member (or base class member)");
static_assert(std::is_same<C, type>::value || std::is_base_of<C, type>::value, "def_readwrite() requires a class member (or base class member)");
cpp_function fget([pm](const type &c) -> const D &{ return c.*pm; }, is_method(*this)),
fset([pm](type &c, const D &value) { c.*pm = value; }, is_method(*this));
def_property(name, fget, fset, return_value_policy::reference_internal, extra...);
@ -1194,7 +1194,7 @@ public:
template <typename C, typename D, typename... Extra>
class_ &def_readonly(const char *name, const D C::*pm, const Extra& ...extra) {
static_assert(std::is_base_of<C, type>::value, "def_readonly() requires a class member (or base class member)");
static_assert(std::is_same<C, type>::value || std::is_base_of<C, type>::value, "def_readonly() requires a class member (or base class member)");
cpp_function fget([pm](const type &c) -> const D &{ return c.*pm; }, is_method(*this));
def_property_readonly(name, fget, return_value_policy::reference_internal, extra...);
return *this;

1
tests/CMakeLists.txt
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@ -59,6 +59,7 @@ set(PYBIND11_TEST_FILES
test_stl.cpp
test_stl_binders.cpp
test_tagbased_polymorphic.cpp
test_union.cpp
test_virtual_functions.cpp
)

22
tests/test_union.cpp Normal file
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@ -0,0 +1,22 @@
/*
tests/test_class.cpp -- test py::class_ definitions and basic functionality
Copyright (c) 2019 Roland Dreier <roland.dreier@gmail.com>
All rights reserved. Use of this source code is governed by a
BSD-style license that can be found in the LICENSE file.
*/
#include "pybind11_tests.h"
TEST_SUBMODULE(union_, m) {
union TestUnion {
int value_int;
unsigned value_uint;
};
py::class_<TestUnion>(m, "TestUnion")
.def(py::init<>())
.def_readonly("as_int", &TestUnion::value_int)
.def_readwrite("as_uint", &TestUnion::value_uint);
}

8
tests/test_union.py Normal file
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@ -0,0 +1,8 @@
from pybind11_tests import union_ as m
def test_union():
instance = m.TestUnion()
instance.as_uint = 10
assert instance.as_int == 10