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

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* 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
6 changed files with 419 additions and 5 deletions
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13
include/pybind11/detail/smart_holder_sfinae_hooks_only.h
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@@ -6,6 +6,7 @@
#include "common.h"
#include <memory>
#include <type_traits>
#ifndef PYBIND11_USE_SMART_HOLDER_AS_DEFAULT
@@ -29,5 +30,17 @@ struct smart_holder_type_caster_base_tag {};
template <typename T>
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(PYBIND11_NAMESPACE)

162
include/pybind11/pybind11.h
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@@ -1514,6 +1514,154 @@ using default_holder_type = smart_holder;
#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>
class class_ : public detail::generic_type {
template <typename T>
@@ -1727,9 +1875,11 @@ public:
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,
"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...);
def_property(name,
property_cpp_function<type, D>::read(pm, *this),
property_cpp_function<type, D>::write(pm, *this),
return_value_policy::reference_internal,
extra...);
return *this;
}
@@ -1737,8 +1887,10 @@ public:
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,
"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...);
def_property_readonly(name,
property_cpp_function<type, D>::readonly(pm, *this),
return_value_policy::reference_internal,
extra...);
return *this;
}