2 pybind11/detail/init.h: init factory function implementation and support code.
4 Copyright (c) 2017 Jason Rhinelander <jason@imaginary.ca>
6 All rights reserved. Use of this source code is governed by a
7 BSD-style license that can be found in the LICENSE file.
14 NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
15 NAMESPACE_BEGIN(detail)
18 class type_caster<value_and_holder> {
20 bool load(handle h, bool) {
21 value = reinterpret_cast<value_and_holder *>(h.ptr());
25 template <typename> using cast_op_type = value_and_holder &;
26 operator value_and_holder &() { return *value; }
27 static constexpr auto name = _<value_and_holder>();
30 value_and_holder *value = nullptr;
33 NAMESPACE_BEGIN(initimpl)
35 inline void no_nullptr(void *ptr) {
36 if (!ptr) throw type_error("pybind11::init(): factory function returned nullptr");
39 // Implementing functions for all forms of py::init<...> and py::init(...)
40 template <typename Class> using Cpp = typename Class::type;
41 template <typename Class> using Alias = typename Class::type_alias;
42 template <typename Class> using Holder = typename Class::holder_type;
44 template <typename Class> using is_alias_constructible = std::is_constructible<Alias<Class>, Cpp<Class> &&>;
46 // Takes a Cpp pointer and returns true if it actually is a polymorphic Alias instance.
47 template <typename Class, enable_if_t<Class::has_alias, int> = 0>
48 bool is_alias(Cpp<Class> *ptr) {
49 return dynamic_cast<Alias<Class> *>(ptr) != nullptr;
51 // Failing fallback version of the above for a no-alias class (always returns false)
52 template <typename /*Class*/>
53 constexpr bool is_alias(void *) { return false; }
55 // Constructs and returns a new object; if the given arguments don't map to a constructor, we fall
56 // back to brace aggregate initiailization so that for aggregate initialization can be used with
57 // py::init, e.g. `py::init<int, int>` to initialize a `struct T { int a; int b; }`. For
58 // non-aggregate types, we need to use an ordinary T(...) constructor (invoking as `T{...}` usually
59 // works, but will not do the expected thing when `T` has an `initializer_list<T>` constructor).
60 template <typename Class, typename... Args, detail::enable_if_t<std::is_constructible<Class, Args...>::value, int> = 0>
61 inline Class *construct_or_initialize(Args &&...args) { return new Class(std::forward<Args>(args)...); }
62 template <typename Class, typename... Args, detail::enable_if_t<!std::is_constructible<Class, Args...>::value, int> = 0>
63 inline Class *construct_or_initialize(Args &&...args) { return new Class{std::forward<Args>(args)...}; }
65 // Attempts to constructs an alias using a `Alias(Cpp &&)` constructor. This allows types with
66 // an alias to provide only a single Cpp factory function as long as the Alias can be
67 // constructed from an rvalue reference of the base Cpp type. This means that Alias classes
68 // can, when appropriate, simply define a `Alias(Cpp &&)` constructor rather than needing to
69 // inherit all the base class constructors.
70 template <typename Class>
71 void construct_alias_from_cpp(std::true_type /*is_alias_constructible*/,
72 value_and_holder &v_h, Cpp<Class> &&base) {
73 v_h.value_ptr() = new Alias<Class>(std::move(base));
75 template <typename Class>
76 [[noreturn]] void construct_alias_from_cpp(std::false_type /*!is_alias_constructible*/,
77 value_and_holder &, Cpp<Class> &&) {
78 throw type_error("pybind11::init(): unable to convert returned instance to required "
79 "alias class: no `Alias<Class>(Class &&)` constructor available");
82 // Error-generating fallback for factories that don't match one of the below construction
84 template <typename Class>
86 static_assert(!std::is_same<Class, Class>::value /* always false */,
87 "pybind11::init(): init function must return a compatible pointer, "
91 // Pointer return v1: the factory function returns a class pointer for a registered class.
92 // If we don't need an alias (because this class doesn't have one, or because the final type is
93 // inherited on the Python side) we can simply take over ownership. Otherwise we need to try to
94 // construct an Alias from the returned base instance.
95 template <typename Class>
96 void construct(value_and_holder &v_h, Cpp<Class> *ptr, bool need_alias) {
98 if (Class::has_alias && need_alias && !is_alias<Class>(ptr)) {
99 // We're going to try to construct an alias by moving the cpp type. Whether or not
100 // that succeeds, we still need to destroy the original cpp pointer (either the
101 // moved away leftover, if the alias construction works, or the value itself if we
102 // throw an error), but we can't just call `delete ptr`: it might have a special
103 // deleter, or might be shared_from_this. So we construct a holder around it as if
104 // it was a normal instance, then steal the holder away into a local variable; thus
105 // the holder and destruction happens when we leave the C++ scope, and the holder
106 // class gets to handle the destruction however it likes.
107 v_h.value_ptr() = ptr;
108 v_h.set_instance_registered(true); // To prevent init_instance from registering it
109 v_h.type->init_instance(v_h.inst, nullptr); // Set up the holder
110 Holder<Class> temp_holder(std::move(v_h.holder<Holder<Class>>())); // Steal the holder
111 v_h.type->dealloc(v_h); // Destroys the moved-out holder remains, resets value ptr to null
112 v_h.set_instance_registered(false);
114 construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(*ptr));
116 // Otherwise the type isn't inherited, so we don't need an Alias
117 v_h.value_ptr() = ptr;
121 // Pointer return v2: a factory that always returns an alias instance ptr. We simply take over
122 // ownership of the pointer.
123 template <typename Class, enable_if_t<Class::has_alias, int> = 0>
124 void construct(value_and_holder &v_h, Alias<Class> *alias_ptr, bool) {
125 no_nullptr(alias_ptr);
126 v_h.value_ptr() = static_cast<Cpp<Class> *>(alias_ptr);
129 // Holder return: copy its pointer, and move or copy the returned holder into the new instance's
130 // holder. This also handles types like std::shared_ptr<T> and std::unique_ptr<T> where T is a
131 // derived type (through those holder's implicit conversion from derived class holder constructors).
132 template <typename Class>
133 void construct(value_and_holder &v_h, Holder<Class> holder, bool need_alias) {
134 auto *ptr = holder_helper<Holder<Class>>::get(holder);
135 // If we need an alias, check that the held pointer is actually an alias instance
136 if (Class::has_alias && need_alias && !is_alias<Class>(ptr))
137 throw type_error("pybind11::init(): construction failed: returned holder-wrapped instance "
138 "is not an alias instance");
140 v_h.value_ptr() = ptr;
141 v_h.type->init_instance(v_h.inst, &holder);
144 // return-by-value version 1: returning a cpp class by value. If the class has an alias and an
145 // alias is required the alias must have an `Alias(Cpp &&)` constructor so that we can construct
146 // the alias from the base when needed (i.e. because of Python-side inheritance). When we don't
147 // need it, we simply move-construct the cpp value into a new instance.
148 template <typename Class>
149 void construct(value_and_holder &v_h, Cpp<Class> &&result, bool need_alias) {
150 static_assert(std::is_move_constructible<Cpp<Class>>::value,
151 "pybind11::init() return-by-value factory function requires a movable class");
152 if (Class::has_alias && need_alias)
153 construct_alias_from_cpp<Class>(is_alias_constructible<Class>{}, v_h, std::move(result));
155 v_h.value_ptr() = new Cpp<Class>(std::move(result));
158 // return-by-value version 2: returning a value of the alias type itself. We move-construct an
159 // Alias instance (even if no the python-side inheritance is involved). The is intended for
160 // cases where Alias initialization is always desired.
161 template <typename Class>
162 void construct(value_and_holder &v_h, Alias<Class> &&result, bool) {
163 static_assert(std::is_move_constructible<Alias<Class>>::value,
164 "pybind11::init() return-by-alias-value factory function requires a movable alias class");
165 v_h.value_ptr() = new Alias<Class>(std::move(result));
168 // Implementing class for py::init<...>()
169 template <typename... Args>
171 template <typename Class, typename... Extra, enable_if_t<!Class::has_alias, int> = 0>
172 static void execute(Class &cl, const Extra&... extra) {
173 cl.def("__init__", [](value_and_holder &v_h, Args... args) {
174 v_h.value_ptr() = construct_or_initialize<Cpp<Class>>(std::forward<Args>(args)...);
175 }, is_new_style_constructor(), extra...);
178 template <typename Class, typename... Extra,
179 enable_if_t<Class::has_alias &&
180 std::is_constructible<Cpp<Class>, Args...>::value, int> = 0>
181 static void execute(Class &cl, const Extra&... extra) {
182 cl.def("__init__", [](value_and_holder &v_h, Args... args) {
183 if (Py_TYPE(v_h.inst) == v_h.type->type)
184 v_h.value_ptr() = construct_or_initialize<Cpp<Class>>(std::forward<Args>(args)...);
186 v_h.value_ptr() = construct_or_initialize<Alias<Class>>(std::forward<Args>(args)...);
187 }, is_new_style_constructor(), extra...);
190 template <typename Class, typename... Extra,
191 enable_if_t<Class::has_alias &&
192 !std::is_constructible<Cpp<Class>, Args...>::value, int> = 0>
193 static void execute(Class &cl, const Extra&... extra) {
194 cl.def("__init__", [](value_and_holder &v_h, Args... args) {
195 v_h.value_ptr() = construct_or_initialize<Alias<Class>>(std::forward<Args>(args)...);
196 }, is_new_style_constructor(), extra...);
200 // Implementing class for py::init_alias<...>()
201 template <typename... Args> struct alias_constructor {
202 template <typename Class, typename... Extra,
203 enable_if_t<Class::has_alias && std::is_constructible<Alias<Class>, Args...>::value, int> = 0>
204 static void execute(Class &cl, const Extra&... extra) {
205 cl.def("__init__", [](value_and_holder &v_h, Args... args) {
206 v_h.value_ptr() = construct_or_initialize<Alias<Class>>(std::forward<Args>(args)...);
207 }, is_new_style_constructor(), extra...);
211 // Implementation class for py::init(Func) and py::init(Func, AliasFunc)
212 template <typename CFunc, typename AFunc = void_type (*)(),
213 typename = function_signature_t<CFunc>, typename = function_signature_t<AFunc>>
216 // Specialization for py::init(Func)
217 template <typename Func, typename Return, typename... Args>
218 struct factory<Func, void_type (*)(), Return(Args...)> {
219 remove_reference_t<Func> class_factory;
221 factory(Func &&f) : class_factory(std::forward<Func>(f)) { }
223 // The given class either has no alias or has no separate alias factory;
224 // this always constructs the class itself. If the class is registered with an alias
225 // type and an alias instance is needed (i.e. because the final type is a Python class
226 // inheriting from the C++ type) the returned value needs to either already be an alias
227 // instance, or the alias needs to be constructible from a `Class &&` argument.
228 template <typename Class, typename... Extra>
229 void execute(Class &cl, const Extra &...extra) && {
230 #if defined(PYBIND11_CPP14)
231 cl.def("__init__", [func = std::move(class_factory)]
233 auto &func = class_factory;
234 cl.def("__init__", [func]
236 (value_and_holder &v_h, Args... args) {
237 construct<Class>(v_h, func(std::forward<Args>(args)...),
238 Py_TYPE(v_h.inst) != v_h.type->type);
239 }, is_new_style_constructor(), extra...);
243 // Specialization for py::init(Func, AliasFunc)
244 template <typename CFunc, typename AFunc,
245 typename CReturn, typename... CArgs, typename AReturn, typename... AArgs>
246 struct factory<CFunc, AFunc, CReturn(CArgs...), AReturn(AArgs...)> {
247 static_assert(sizeof...(CArgs) == sizeof...(AArgs),
248 "pybind11::init(class_factory, alias_factory): class and alias factories "
249 "must have identical argument signatures");
250 static_assert(all_of<std::is_same<CArgs, AArgs>...>::value,
251 "pybind11::init(class_factory, alias_factory): class and alias factories "
252 "must have identical argument signatures");
254 remove_reference_t<CFunc> class_factory;
255 remove_reference_t<AFunc> alias_factory;
257 factory(CFunc &&c, AFunc &&a)
258 : class_factory(std::forward<CFunc>(c)), alias_factory(std::forward<AFunc>(a)) { }
260 // The class factory is called when the `self` type passed to `__init__` is the direct
261 // class (i.e. not inherited), the alias factory when `self` is a Python-side subtype.
262 template <typename Class, typename... Extra>
263 void execute(Class &cl, const Extra&... extra) && {
264 static_assert(Class::has_alias, "The two-argument version of `py::init()` can "
265 "only be used if the class has an alias");
266 #if defined(PYBIND11_CPP14)
267 cl.def("__init__", [class_func = std::move(class_factory), alias_func = std::move(alias_factory)]
269 auto &class_func = class_factory;
270 auto &alias_func = alias_factory;
271 cl.def("__init__", [class_func, alias_func]
273 (value_and_holder &v_h, CArgs... args) {
274 if (Py_TYPE(v_h.inst) == v_h.type->type)
275 // If the instance type equals the registered type we don't have inheritance, so
276 // don't need the alias and can construct using the class function:
277 construct<Class>(v_h, class_func(std::forward<CArgs>(args)...), false);
279 construct<Class>(v_h, alias_func(std::forward<CArgs>(args)...), true);
280 }, is_new_style_constructor(), extra...);
284 /// Set just the C++ state. Same as `__init__`.
285 template <typename Class, typename T>
286 void setstate(value_and_holder &v_h, T &&result, bool need_alias) {
287 construct<Class>(v_h, std::forward<T>(result), need_alias);
290 /// Set both the C++ and Python states
291 template <typename Class, typename T, typename O,
292 enable_if_t<std::is_convertible<O, handle>::value, int> = 0>
293 void setstate(value_and_holder &v_h, std::pair<T, O> &&result, bool need_alias) {
294 construct<Class>(v_h, std::move(result.first), need_alias);
295 setattr((PyObject *) v_h.inst, "__dict__", result.second);
298 /// Implementation for py::pickle(GetState, SetState)
299 template <typename Get, typename Set,
300 typename = function_signature_t<Get>, typename = function_signature_t<Set>>
301 struct pickle_factory;
303 template <typename Get, typename Set,
304 typename RetState, typename Self, typename NewInstance, typename ArgState>
305 struct pickle_factory<Get, Set, RetState(Self), NewInstance(ArgState)> {
306 static_assert(std::is_same<intrinsic_t<RetState>, intrinsic_t<ArgState>>::value,
307 "The type returned by `__getstate__` must be the same "
308 "as the argument accepted by `__setstate__`");
310 remove_reference_t<Get> get;
311 remove_reference_t<Set> set;
313 pickle_factory(Get get, Set set)
314 : get(std::forward<Get>(get)), set(std::forward<Set>(set)) { }
316 template <typename Class, typename... Extra>
317 void execute(Class &cl, const Extra &...extra) && {
318 cl.def("__getstate__", std::move(get));
320 #if defined(PYBIND11_CPP14)
321 cl.def("__setstate__", [func = std::move(set)]
324 cl.def("__setstate__", [func]
326 (value_and_holder &v_h, ArgState state) {
327 setstate<Class>(v_h, func(std::forward<ArgState>(state)),
328 Py_TYPE(v_h.inst) != v_h.type->type);
329 }, is_new_style_constructor(), extra...);
333 NAMESPACE_END(initimpl)
334 NAMESPACE_END(detail)
335 NAMESPACE_END(pybind11)