[smart_holder] .def_readonly, .def_readwrite adaptors (continuation of PR #3581). (#3844)

* Transferred net diff from PR #3581, as-is.

* Automatic `pre-commit run --all-files` fixes. NO manual changes.

* Removing trailing `//` (originally added to manipulate clang-format), as suggested by @charlesbeattie back in Jan/Feb under PR #3581.

* Renaming `xetter_cpp_function` to `property_cpp_function` as suggested by @rainwoodman

* Fully explain the terse variable naming scheme in test_class_sh_property (as suggested by @rainwoodman)

* Also use parametrize for readonly, readwrite (as suggested by @rainwoodman)

* Apply change suggested by @skylion007 (with clang-format).
This commit is contained in:
Ralf W. Grosse-Kunstleve 2022-05-17 16:35:43 -07:00 committed by GitHub
parent aebdf00cd0
commit d28c3a5da7
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6 changed files with 419 additions and 5 deletions

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@ -11,3 +11,4 @@ atyp_valu rtrn_valu() { atyp_valu obj{"Valu"}; return obj; }
valu = other.valu; valu = other.valu;
with pytest.raises(ValueError) as excinfo: with pytest.raises(ValueError) as excinfo:
with pytest.raises(ValueError) as exc_info: with pytest.raises(ValueError) as exc_info:
// valu(e), ref(erence), ptr or p (pointer), r = rvalue, m = mutable, c = const,

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@ -6,6 +6,7 @@
#include "common.h" #include "common.h"
#include <memory>
#include <type_traits> #include <type_traits>
#ifndef PYBIND11_USE_SMART_HOLDER_AS_DEFAULT #ifndef PYBIND11_USE_SMART_HOLDER_AS_DEFAULT
@ -29,5 +30,17 @@ struct smart_holder_type_caster_base_tag {};
template <typename T> template <typename T>
struct type_uses_smart_holder_type_caster; struct type_uses_smart_holder_type_caster;
// Simple helpers that may eventually be a better fit for another header file:
template <typename T>
struct is_std_unique_ptr : std::false_type {};
template <typename T, typename D>
struct is_std_unique_ptr<std::unique_ptr<T, D>> : std::true_type {};
template <typename T>
struct is_std_shared_ptr : std::false_type {};
template <typename T>
struct is_std_shared_ptr<std::shared_ptr<T>> : std::true_type {};
PYBIND11_NAMESPACE_END(detail) PYBIND11_NAMESPACE_END(detail)
PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE) PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

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@ -1514,6 +1514,154 @@ using default_holder_type = smart_holder;
#endif #endif
// Helper for the property_cpp_function static member functions below.
// The only purpose of these functions is to support .def_readonly & .def_readwrite.
// In this context, the PM template parameter is certain to be a Pointer to a Member.
// The main purpose of must_be_member_function_pointer is to make this obvious, and to guard
// against accidents. As a side-effect, it also explains why the syntactical overhead for
// perfect forwarding is not needed.
template <typename PM>
using must_be_member_function_pointer
= detail::enable_if_t<std::is_member_pointer<PM>::value, int>;
// Note that property_cpp_function is intentionally in the main pybind11 namespace,
// because user-defined specializations could be useful.
// Classic (non-smart_holder) implementations for .def_readonly and .def_readwrite
// getter and setter functions.
// WARNING: This classic implementation can lead to dangling pointers for raw pointer members.
// See test_ptr() in tests/test_class_sh_property.py
// This implementation works as-is (and safely) for smart_holder std::shared_ptr members.
template <typename T, typename D, typename SFINAE = void>
struct property_cpp_function {
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function readonly(PM pm, const handle &hdl) {
return cpp_function([pm](const T &c) -> const D & { return c.*pm; }, is_method(hdl));
}
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function read(PM pm, const handle &hdl) {
return readonly(pm, hdl);
}
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function write(PM pm, const handle &hdl) {
return cpp_function([pm](T &c, const D &value) { c.*pm = value; }, is_method(hdl));
}
};
// smart_holder specializations for raw pointer members.
// WARNING: Like the classic implementation, this implementation can lead to dangling pointers.
// See test_ptr() in tests/test_class_sh_property.py
// However, the read functions return a shared_ptr to the member, emulating the PyCLIF approach:
// https://github.com/google/clif/blob/c371a6d4b28d25d53a16e6d2a6d97305fb1be25a/clif/python/instance.h#L233
// This prevents disowning of the Python object owning the raw pointer member.
template <typename T, typename D>
struct property_cpp_function<
T,
D,
detail::enable_if_t<detail::all_of<detail::type_uses_smart_holder_type_caster<T>,
detail::type_uses_smart_holder_type_caster<D>,
std::is_pointer<D>>::value>> {
using drp = typename std::remove_pointer<D>::type;
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function readonly(PM pm, const handle &hdl) {
return cpp_function(
[pm](const std::shared_ptr<T> &c_sp) -> std::shared_ptr<drp> {
D ptr = (*c_sp).*pm;
return std::shared_ptr<drp>(c_sp, ptr);
},
is_method(hdl));
}
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function read(PM pm, const handle &hdl) {
return readonly(pm, hdl);
}
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function write(PM pm, const handle &hdl) {
return cpp_function([pm](T &c, D value) { c.*pm = std::forward<D>(value); },
is_method(hdl));
}
};
// smart_holder specializations for members held by-value.
// The read functions return a shared_ptr to the member, emulating the PyCLIF approach:
// https://github.com/google/clif/blob/c371a6d4b28d25d53a16e6d2a6d97305fb1be25a/clif/python/instance.h#L233
// This prevents disowning of the Python object owning the member.
template <typename T, typename D>
struct property_cpp_function<
T,
D,
detail::enable_if_t<detail::all_of<detail::type_uses_smart_holder_type_caster<T>,
detail::type_uses_smart_holder_type_caster<D>,
detail::none_of<std::is_pointer<D>,
detail::is_std_unique_ptr<D>,
detail::is_std_shared_ptr<D>>>::value>> {
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function readonly(PM pm, const handle &hdl) {
return cpp_function(
[pm](const std::shared_ptr<T> &c_sp)
-> std::shared_ptr<typename std::add_const<D>::type> {
return std::shared_ptr<typename std::add_const<D>::type>(c_sp, &(c_sp.get()->*pm));
},
is_method(hdl));
}
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function read(PM pm, const handle &hdl) {
return cpp_function(
[pm](const std::shared_ptr<T> &c_sp) -> std::shared_ptr<D> {
return std::shared_ptr<D>(c_sp, &(c_sp.get()->*pm));
},
is_method(hdl));
}
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function write(PM pm, const handle &hdl) {
return cpp_function([pm](T &c, const D &value) { c.*pm = value; }, is_method(hdl));
}
};
// smart_holder specializations for std::unique_ptr members.
// read disowns the member unique_ptr.
// write disowns the passed Python object.
// readonly is disabled (static_assert) because there is no safe & intuitive way to make the member
// accessible as a Python object without disowning the member unique_ptr. A .def_readonly disowning
// the unique_ptr member is deemed highly prone to misunderstandings.
template <typename T, typename D>
struct property_cpp_function<
T,
D,
detail::enable_if_t<detail::all_of<
detail::type_uses_smart_holder_type_caster<T>,
detail::is_std_unique_ptr<D>,
detail::type_uses_smart_holder_type_caster<typename D::element_type>>::value>> {
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function readonly(PM, const handle &) {
static_assert(!detail::is_std_unique_ptr<D>::value,
"def_readonly cannot be used for std::unique_ptr members.");
return cpp_function{}; // Unreachable.
}
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function read(PM pm, const handle &hdl) {
return cpp_function(
[pm](const std::shared_ptr<T> &c_sp) -> D { return D{std::move(c_sp.get()->*pm)}; },
is_method(hdl));
}
template <typename PM, must_be_member_function_pointer<PM> = 0>
static cpp_function write(PM pm, const handle &hdl) {
return cpp_function([pm](T &c, D &&value) { c.*pm = std::move(value); }, is_method(hdl));
}
};
template <typename type_, typename... options> template <typename type_, typename... options>
class class_ : public detail::generic_type { class class_ : public detail::generic_type {
template <typename T> template <typename T>
@ -1727,9 +1875,11 @@ public:
class_ &def_readwrite(const char *name, D C::*pm, const Extra &...extra) { class_ &def_readwrite(const char *name, D C::*pm, const Extra &...extra) {
static_assert(std::is_same<C, type>::value || std::is_base_of<C, type>::value, 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)"); "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)), def_property(name,
fset([pm](type &c, const D &value) { c.*pm = value; }, is_method(*this)); property_cpp_function<type, D>::read(pm, *this),
def_property(name, fget, fset, return_value_policy::reference_internal, extra...); property_cpp_function<type, D>::write(pm, *this),
return_value_policy::reference_internal,
extra...);
return *this; return *this;
} }
@ -1737,8 +1887,10 @@ public:
class_ &def_readonly(const char *name, const D C::*pm, const Extra &...extra) { class_ &def_readonly(const char *name, const D C::*pm, const Extra &...extra) {
static_assert(std::is_same<C, type>::value || std::is_base_of<C, type>::value, 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)"); "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,
def_property_readonly(name, fget, return_value_policy::reference_internal, extra...); property_cpp_function<type, D>::readonly(pm, *this),
return_value_policy::reference_internal,
extra...);
return *this; return *this;
} }

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@ -128,6 +128,7 @@ set(PYBIND11_TEST_FILES
test_class_sh_factory_constructors test_class_sh_factory_constructors
test_class_sh_inheritance test_class_sh_inheritance
test_class_sh_module_local.py test_class_sh_module_local.py
test_class_sh_property
test_class_sh_shared_ptr_copy_move test_class_sh_shared_ptr_copy_move
test_class_sh_trampoline_basic test_class_sh_trampoline_basic
test_class_sh_trampoline_self_life_support test_class_sh_trampoline_self_life_support

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@ -0,0 +1,86 @@
// The compact 4-character naming matches that in test_class_sh_basic.cpp
// Variable names are intentionally terse, to not distract from the more important C++ type names:
// valu(e), ref(erence), ptr or p (pointer), r = rvalue, m = mutable, c = const,
// sh = shared_ptr, uq = unique_ptr.
#include "pybind11/smart_holder.h"
#include "pybind11_tests.h"
#include <memory>
namespace test_class_sh_property {
struct ClassicField {
int num = -88;
};
struct ClassicOuter {
ClassicField *m_mptr = nullptr;
const ClassicField *m_cptr = nullptr;
};
struct Field {
int num = -99;
};
struct Outer {
Field m_valu;
Field *m_mptr = nullptr;
const Field *m_cptr = nullptr;
std::unique_ptr<Field> m_uqmp;
std::unique_ptr<const Field> m_uqcp;
std::shared_ptr<Field> m_shmp;
std::shared_ptr<const Field> m_shcp;
};
inline void DisownOuter(std::unique_ptr<Outer>) {}
} // namespace test_class_sh_property
PYBIND11_TYPE_CASTER_BASE_HOLDER(test_class_sh_property::ClassicField,
std::unique_ptr<test_class_sh_property::ClassicField>)
PYBIND11_TYPE_CASTER_BASE_HOLDER(test_class_sh_property::ClassicOuter,
std::unique_ptr<test_class_sh_property::ClassicOuter>)
PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_property::Field)
PYBIND11_SMART_HOLDER_TYPE_CASTERS(test_class_sh_property::Outer)
TEST_SUBMODULE(class_sh_property, m) {
using namespace test_class_sh_property;
py::class_<ClassicField, std::unique_ptr<ClassicField>>(m, "ClassicField")
.def(py::init<>())
.def_readwrite("num", &ClassicField::num);
py::class_<ClassicOuter, std::unique_ptr<ClassicOuter>>(m, "ClassicOuter")
.def(py::init<>())
.def_readonly("m_mptr_readonly", &ClassicOuter::m_mptr)
.def_readwrite("m_mptr_readwrite", &ClassicOuter::m_mptr)
.def_readwrite("m_cptr_readonly", &ClassicOuter::m_cptr)
.def_readwrite("m_cptr_readwrite", &ClassicOuter::m_cptr);
py::classh<Field>(m, "Field").def(py::init<>()).def_readwrite("num", &Field::num);
py::classh<Outer>(m, "Outer")
.def(py::init<>())
.def_readonly("m_valu_readonly", &Outer::m_valu)
.def_readwrite("m_valu_readwrite", &Outer::m_valu)
.def_readonly("m_mptr_readonly", &Outer::m_mptr)
.def_readwrite("m_mptr_readwrite", &Outer::m_mptr)
.def_readonly("m_cptr_readonly", &Outer::m_cptr)
.def_readwrite("m_cptr_readwrite", &Outer::m_cptr)
// .def_readonly("m_uqmp_readonly", &Outer::m_uqmp) // Custom compilation Error.
.def_readwrite("m_uqmp_readwrite", &Outer::m_uqmp)
// .def_readonly("m_uqcp_readonly", &Outer::m_uqcp) // Custom compilation Error.
.def_readwrite("m_uqcp_readwrite", &Outer::m_uqcp)
.def_readwrite("m_shmp_readonly", &Outer::m_shmp)
.def_readwrite("m_shmp_readwrite", &Outer::m_shmp)
.def_readwrite("m_shcp_readonly", &Outer::m_shcp)
.def_readwrite("m_shcp_readwrite", &Outer::m_shcp);
m.def("DisownOuter", DisownOuter);
}

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@ -0,0 +1,161 @@
# The compact 4-character naming scheme (e.g. mptr, cptr, shcp) is explained at the top of
# test_class_sh_property.cpp.
import pytest
import env # noqa: F401
from pybind11_tests import class_sh_property as m
@pytest.mark.xfail("env.PYPY", reason="gc after `del field` is apparently deferred")
@pytest.mark.parametrize("m_attr", ("m_valu_readonly", "m_valu_readwrite"))
def test_valu_getter(msg, m_attr):
# Reduced from PyCLIF test:
# https://github.com/google/clif/blob/c371a6d4b28d25d53a16e6d2a6d97305fb1be25a/clif/testing/python/nested_fields_test.py#L56
outer = m.Outer()
field = getattr(outer, m_attr)
assert field.num == -99
with pytest.raises(ValueError) as excinfo:
m.DisownOuter(outer)
assert msg(excinfo.value) == "Cannot disown use_count != 1 (loaded_as_unique_ptr)."
del field
m.DisownOuter(outer)
with pytest.raises(ValueError) as excinfo:
getattr(outer, m_attr)
assert (
msg(excinfo.value)
== "Missing value for wrapped C++ type: Python instance was disowned."
)
def test_valu_setter():
outer = m.Outer()
assert outer.m_valu_readonly.num == -99
assert outer.m_valu_readwrite.num == -99
field = m.Field()
field.num = 35
outer.m_valu_readwrite = field
assert outer.m_valu_readonly.num == 35
assert outer.m_valu_readwrite.num == 35
@pytest.mark.parametrize("m_attr", ("m_shmp", "m_shcp"))
def test_shp(m_attr):
m_attr_readonly = m_attr + "_readonly"
m_attr_readwrite = m_attr + "_readwrite"
outer = m.Outer()
assert getattr(outer, m_attr_readonly) is None
assert getattr(outer, m_attr_readwrite) is None
field = m.Field()
field.num = 43
setattr(outer, m_attr_readwrite, field)
assert getattr(outer, m_attr_readonly).num == 43
assert getattr(outer, m_attr_readwrite).num == 43
getattr(outer, m_attr_readonly).num = 57
getattr(outer, m_attr_readwrite).num = 57
assert field.num == 57
del field
assert getattr(outer, m_attr_readonly).num == 57
assert getattr(outer, m_attr_readwrite).num == 57
@pytest.mark.parametrize(
"field_type, num_default, outer_type",
[
(m.ClassicField, -88, m.ClassicOuter),
(m.Field, -99, m.Outer),
],
)
@pytest.mark.parametrize("m_attr", ("m_mptr", "m_cptr"))
@pytest.mark.parametrize("r_kind", ("_readonly", "_readwrite"))
def test_ptr(field_type, num_default, outer_type, m_attr, r_kind):
m_attr_r_kind = m_attr + r_kind
outer = outer_type()
assert getattr(outer, m_attr_r_kind) is None
field = field_type()
assert field.num == num_default
setattr(outer, m_attr + "_readwrite", field)
assert getattr(outer, m_attr_r_kind).num == num_default
field.num = 76
assert getattr(outer, m_attr_r_kind).num == 76
# Change to -88 or -99 to demonstrate Undefined Behavior (dangling pointer).
if num_default == 88 and m_attr == "m_mptr":
del field
assert getattr(outer, m_attr_r_kind).num == 76
@pytest.mark.parametrize("m_attr_readwrite", ("m_uqmp_readwrite", "m_uqcp_readwrite"))
def test_uqp(m_attr_readwrite, msg):
outer = m.Outer()
assert getattr(outer, m_attr_readwrite) is None
field_orig = m.Field()
field_orig.num = 39
setattr(outer, m_attr_readwrite, field_orig)
with pytest.raises(ValueError) as excinfo:
field_orig.num
assert (
msg(excinfo.value)
== "Missing value for wrapped C++ type: Python instance was disowned."
)
field_retr1 = getattr(outer, m_attr_readwrite)
assert getattr(outer, m_attr_readwrite) is None
assert field_retr1.num == 39
field_retr1.num = 93
setattr(outer, m_attr_readwrite, field_retr1)
with pytest.raises(ValueError):
field_retr1.num
field_retr2 = getattr(outer, m_attr_readwrite)
assert field_retr2.num == 93
# Proof-of-concept (POC) for safe & intuitive Python access to unique_ptr members.
# The C++ member unique_ptr is disowned to a temporary Python object for accessing
# an attribute of the member. After the attribute was accessed, the Python object
# is disowned back to the C++ member unique_ptr.
# Productizing this POC is left for a future separate PR, as needed.
class unique_ptr_field_proxy_poc: # noqa: N801
def __init__(self, obj, field_name):
object.__setattr__(self, "__obj", obj)
object.__setattr__(self, "__field_name", field_name)
def __getattr__(self, *args, **kwargs):
return _proxy_dereference(self, getattr, *args, **kwargs)
def __setattr__(self, *args, **kwargs):
return _proxy_dereference(self, setattr, *args, **kwargs)
def __delattr__(self, *args, **kwargs):
return _proxy_dereference(self, delattr, *args, **kwargs)
def _proxy_dereference(proxy, xxxattr, *args, **kwargs):
obj = object.__getattribute__(proxy, "__obj")
field_name = object.__getattribute__(proxy, "__field_name")
field = getattr(obj, field_name) # Disowns the C++ unique_ptr member.
assert field is not None
try:
return xxxattr(field, *args, **kwargs)
finally:
setattr(obj, field_name, field) # Disowns the temporary Python object (field).
@pytest.mark.parametrize("m_attr", ("m_uqmp", "m_uqcp"))
def test_unique_ptr_field_proxy_poc(m_attr, msg):
m_attr_readwrite = m_attr + "_readwrite"
outer = m.Outer()
field_orig = m.Field()
field_orig.num = 45
setattr(outer, m_attr_readwrite, field_orig)
field_proxy = unique_ptr_field_proxy_poc(outer, m_attr_readwrite)
assert field_proxy.num == 45
assert field_proxy.num == 45
with pytest.raises(AttributeError):
field_proxy.xyz
assert field_proxy.num == 45
field_proxy.num = 82
assert field_proxy.num == 82
field_proxy = unique_ptr_field_proxy_poc(outer, m_attr_readwrite)
assert field_proxy.num == 82
with pytest.raises(AttributeError):
del field_proxy.num
assert field_proxy.num == 82