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 /*
     pybind11/detail/class.h: Python C API implementation details for py::class_
 
     Copyright (c) 2017 Wenzel Jakob <wenzel.jakob@epfl.ch>
 
     All rights reserved. Use of this source code is governed by a
     BSD-style license that can be found in the LICENSE file.
 */
 
 #pragma once
 
 #include <pybind11/attr.h>
 #include <pybind11/options.h>
 
 #include "exception_translation.h"
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 PYBIND11_NAMESPACE_BEGIN(detail)
 
 #if !defined(PYPY_VERSION)
 #    define PYBIND11_BUILTIN_QUALNAME
 #    define PYBIND11_SET_OLDPY_QUALNAME(obj, nameobj)
 #else
 // In PyPy, we still set __qualname__ so that we can produce reliable function type
 // signatures; in CPython this macro expands to nothing:
 #    define PYBIND11_SET_OLDPY_QUALNAME(obj, nameobj)                                             \
         setattr((PyObject *) obj, "__qualname__", nameobj)
 #endif
 
 inline std::string get_fully_qualified_tp_name(PyTypeObject *type) {
 #if !defined(PYPY_VERSION)
     return type->tp_name;
 #else
     auto module_name = handle((PyObject *) type).attr("__module__").cast<std::string>();
     if (module_name == PYBIND11_BUILTINS_MODULE)
         return type->tp_name;
     else
         return std::move(module_name) + "." + type->tp_name;
 #endif
 }
 
 inline PyTypeObject *type_incref(PyTypeObject *type) {
     Py_INCREF(type);
     return type;
 }
 
 #if !defined(PYPY_VERSION)
 
 /// `pybind11_static_property.__get__()`: Always pass the class instead of the instance.
 extern "C" inline PyObject *pybind11_static_get(PyObject *self, PyObject * /*ob*/, PyObject *cls) {
     return PyProperty_Type.tp_descr_get(self, cls, cls);
 }
 
 /// `pybind11_static_property.__set__()`: Just like the above `__get__()`.
 extern "C" inline int pybind11_static_set(PyObject *self, PyObject *obj, PyObject *value) {
     PyObject *cls = PyType_Check(obj) ? obj : (PyObject *) Py_TYPE(obj);
     return PyProperty_Type.tp_descr_set(self, cls, value);
 }
 
 // Forward declaration to use in `make_static_property_type()`
 inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type);
 
 /** A `static_property` is the same as a `property` but the `__get__()` and `__set__()`
     methods are modified to always use the object type instead of a concrete instance.
     Return value: New reference. */
 inline PyTypeObject *make_static_property_type() {
     constexpr auto *name = "pybind11_static_property";
     auto name_obj = reinterpret_steal<object>(PYBIND11_FROM_STRING(name));
 
     /* Danger zone: from now (and until PyType_Ready), make sure to
        issue no Python C API calls which could potentially invoke the
        garbage collector (the GC will call type_traverse(), which will in
        turn find the newly constructed type in an invalid state) */
     auto *heap_type = reinterpret_cast<PyHeapTypeObject *>(PyType_Type.tp_alloc(&PyType_Type, 0));
     if (!heap_type) {
         pybind11_fail("make_static_property_type(): error allocating type!");
     }
 
     heap_type->ht_name = name_obj.inc_ref().ptr();
 #    ifdef PYBIND11_BUILTIN_QUALNAME
     heap_type->ht_qualname = name_obj.inc_ref().ptr();
 #    endif
 
     auto *type = &heap_type->ht_type;
     type->tp_name = name;
     type->tp_base = type_incref(&PyProperty_Type);
     type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HEAPTYPE;
     type->tp_descr_get = pybind11_static_get;
     type->tp_descr_set = pybind11_static_set;
 
 #    if PY_VERSION_HEX >= 0x030C0000
     // Since Python-3.12 property-derived types are required to
     // have dynamic attributes (to set `__doc__`)
     enable_dynamic_attributes(heap_type);
 #    endif
 
     if (PyType_Ready(type) < 0) {
         pybind11_fail("make_static_property_type(): failure in PyType_Ready()!");
     }
 
     setattr(reinterpret_cast<PyObject *>(type), "__module__", str(PYBIND11_DUMMY_MODULE_NAME));
     PYBIND11_SET_OLDPY_QUALNAME(type, name_obj);
 
     return type;
 }
 
 #else // PYPY
 
 /** PyPy has some issues with the above C API, so we evaluate Python code instead.
     This function will only be called once so performance isn't really a concern.
     Return value: New reference. */
 inline PyTypeObject *make_static_property_type() {
     auto d = dict();
     PyObject *result = PyRun_String(R"(\
 class pybind11_static_property(property):
     def __get__(self, obj, cls):
         return property.__get__(self, cls, cls)
 
     def __set__(self, obj, value):
         cls = obj if isinstance(obj, type) else type(obj)
         property.__set__(self, cls, value)
 )",
                                     Py_file_input,
                                     d.ptr(),
                                     d.ptr());
     if (result == nullptr)
         throw error_already_set();
     Py_DECREF(result);
     return (PyTypeObject *) d["pybind11_static_property"].cast<object>().release().ptr();
 }
 
 #endif // PYPY
 
 /** Types with static properties need to handle `Type.static_prop = x` in a specific way.
     By default, Python replaces the `static_property` itself, but for wrapped C++ types
     we need to call `static_property.__set__()` in order to propagate the new value to
     the underlying C++ data structure. */
 extern "C" inline int pybind11_meta_setattro(PyObject *obj, PyObject *name, PyObject *value) {
     // Use `_PyType_Lookup()` instead of `PyObject_GetAttr()` in order to get the raw
     // descriptor (`property`) instead of calling `tp_descr_get` (`property.__get__()`).
     PyObject *descr = _PyType_Lookup((PyTypeObject *) obj, name);
 
     // The following assignment combinations are possible:
     //   1. `Type.static_prop = value`             --> descr_set: `Type.static_prop.__set__(value)`
     //   2. `Type.static_prop = other_static_prop` --> setattro:  replace existing `static_prop`
     //   3. `Type.regular_attribute = value`       --> setattro:  regular attribute assignment
     auto *const static_prop = (PyObject *) get_internals().static_property_type;
     const auto call_descr_set = (descr != nullptr) && (value != nullptr)
                                 && (PyObject_IsInstance(descr, static_prop) != 0)
                                 && (PyObject_IsInstance(value, static_prop) == 0);
     if (call_descr_set) {
         // Call `static_property.__set__()` instead of replacing the `static_property`.
 #if !defined(PYPY_VERSION)
         return Py_TYPE(descr)->tp_descr_set(descr, obj, value);
 #else
         if (PyObject *result = PyObject_CallMethod(descr, "__set__", "OO", obj, value)) {
             Py_DECREF(result);
             return 0;
         } else {
             return -1;
         }
 #endif
     } else {
         // Replace existing attribute.
         return PyType_Type.tp_setattro(obj, name, value);
     }
 }
 
 /**
  * Python 3's PyInstanceMethod_Type hides itself via its tp_descr_get, which prevents aliasing
  * methods via cls.attr("m2") = cls.attr("m1"): instead the tp_descr_get returns a plain function,
  * when called on a class, or a PyMethod, when called on an instance.  Override that behaviour here
  * to do a special case bypass for PyInstanceMethod_Types.
  */
 extern "C" inline PyObject *pybind11_meta_getattro(PyObject *obj, PyObject *name) {
     PyObject *descr = _PyType_Lookup((PyTypeObject *) obj, name);
     if (descr && PyInstanceMethod_Check(descr)) {
         Py_INCREF(descr);
         return descr;
     }
     return PyType_Type.tp_getattro(obj, name);
 }
 
 /// metaclass `__call__` function that is used to create all pybind11 objects.
 extern "C" inline PyObject *pybind11_meta_call(PyObject *type, PyObject *args, PyObject *kwargs) {
 
     // use the default metaclass call to create/initialize the object
     PyObject *self = PyType_Type.tp_call(type, args, kwargs);
     if (self == nullptr) {
         return nullptr;
     }
 
     // Ensure that the base __init__ function(s) were called
     values_and_holders vhs(self);
     for (const auto &vh : vhs) {
         if (!vh.holder_constructed() && !vhs.is_redundant_value_and_holder(vh)) {
             PyErr_Format(PyExc_TypeError,
                          "%.200s.__init__() must be called when overriding __init__",
                          get_fully_qualified_tp_name(vh.type->type).c_str());
             Py_DECREF(self);
             return nullptr;
         }
     }
 
     return self;
 }
 
 /// Cleanup the type-info for a pybind11-registered type.
 extern "C" inline void pybind11_meta_dealloc(PyObject *obj) {
     with_internals_if_internals([obj](internals &internals) {
         auto *type = (PyTypeObject *) obj;
 
         // A pybind11-registered type will:
         // 1) be found in internals.registered_types_py
         // 2) have exactly one associated `detail::type_info`
         auto found_type = internals.registered_types_py.find(type);
         if (found_type != internals.registered_types_py.end() && found_type->second.size() == 1
             && found_type->second[0]->type == type) {
 
             auto *tinfo = found_type->second[0];
             auto tindex = std::type_index(*tinfo->cpptype);
             internals.direct_conversions.erase(tindex);
 
             auto &local_internals = get_local_internals();
             if (tinfo->module_local) {
                 local_internals.registered_types_cpp.erase(tinfo->cpptype);
             } else {
                 internals.registered_types_cpp.erase(tindex);
 #if PYBIND11_INTERNALS_VERSION >= 12
                 internals.registered_types_cpp_fast.erase(tinfo->cpptype);
                 for (const std::type_info *alias : tinfo->alias_chain) {
                     auto num_erased = internals.registered_types_cpp_fast.erase(alias);
                     (void) num_erased;
                     assert(num_erased > 0);
                 }
 #endif
             }
             internals.registered_types_py.erase(tinfo->type);
 
             // Actually just `std::erase_if`, but that's only available in C++20
             auto &cache = internals.inactive_override_cache;
             for (auto it = cache.begin(), last = cache.end(); it != last;) {
                 if (it->first == (PyObject *) tinfo->type) {
                     it = cache.erase(it);
                 } else {
                     ++it;
                 }
             }
 
             delete tinfo;
         }
     });
 
     PyType_Type.tp_dealloc(obj);
 }
 
 /** This metaclass is assigned by default to all pybind11 types and is required in order
     for static properties to function correctly. Users may override this using `py::metaclass`.
     Return value: New reference. */
 inline PyTypeObject *make_default_metaclass() {
     constexpr auto *name = "pybind11_type";
     auto name_obj = reinterpret_steal<object>(PYBIND11_FROM_STRING(name));
 
     /* Danger zone: from now (and until PyType_Ready), make sure to
        issue no Python C API calls which could potentially invoke the
        garbage collector (the GC will call type_traverse(), which will in
        turn find the newly constructed type in an invalid state) */
     auto *heap_type = reinterpret_cast<PyHeapTypeObject *>(PyType_Type.tp_alloc(&PyType_Type, 0));
     if (!heap_type) {
         pybind11_fail("make_default_metaclass(): error allocating metaclass!");
     }
 
     heap_type->ht_name = name_obj.inc_ref().ptr();
 #ifdef PYBIND11_BUILTIN_QUALNAME
     heap_type->ht_qualname = name_obj.inc_ref().ptr();
 #endif
 
     auto *type = &heap_type->ht_type;
     type->tp_name = name;
     type->tp_base = type_incref(&PyType_Type);
     type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HEAPTYPE;
 
     type->tp_call = pybind11_meta_call;
 
     type->tp_setattro = pybind11_meta_setattro;
     type->tp_getattro = pybind11_meta_getattro;
 
     type->tp_dealloc = pybind11_meta_dealloc;
 
     if (PyType_Ready(type) < 0) {
         pybind11_fail("make_default_metaclass(): failure in PyType_Ready()!");
     }
 
     setattr(reinterpret_cast<PyObject *>(type), "__module__", str(PYBIND11_DUMMY_MODULE_NAME));
     PYBIND11_SET_OLDPY_QUALNAME(type, name_obj);
 
     return type;
 }
 
 /// For multiple inheritance types we need to recursively register/deregister base pointers for any
 /// base classes with pointers that are difference from the instance value pointer so that we can
 /// correctly recognize an offset base class pointer. This calls a function with any offset base
 /// ptrs.
 inline void traverse_offset_bases(void *valueptr,
                                   const detail::type_info *tinfo,
                                   instance *self,
                                   bool (*f)(void * /*parentptr*/, instance * /*self*/)) {
     for (handle h : reinterpret_borrow<tuple>(tinfo->type->tp_bases)) {
         if (auto *parent_tinfo = get_type_info(reinterpret_cast<PyTypeObject *>(h.ptr()))) {
             for (auto &c : parent_tinfo->implicit_casts) {
                 if (c.first == tinfo->cpptype) {
                     auto *parentptr = c.second(valueptr);
                     if (parentptr != valueptr) {
                         f(parentptr, self);
                     }
                     traverse_offset_bases(parentptr, parent_tinfo, self, f);
                     break;
                 }
             }
         }
     }
 }
 
 #ifdef Py_GIL_DISABLED
 inline void enable_try_inc_ref(PyObject *obj) {
 #    if PY_VERSION_HEX >= 0x030E00A4
     PyUnstable_EnableTryIncRef(obj);
 #    else
     if (_Py_IsImmortal(obj)) {
         return;
     }
     for (;;) {
         Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&obj->ob_ref_shared);
         if ((shared & _Py_REF_SHARED_FLAG_MASK) != 0) {
             // Nothing to do if it's in WEAKREFS, QUEUED, or MERGED states.
             return;
         }
         if (_Py_atomic_compare_exchange_ssize(
                 &obj->ob_ref_shared, &shared, shared | _Py_REF_MAYBE_WEAKREF)) {
             return;
         }
     }
 #    endif
 }
 #endif
 
 inline bool register_instance_impl(void *ptr, instance *self) {
     assert(ptr);
 #ifdef Py_GIL_DISABLED
     enable_try_inc_ref(reinterpret_cast<PyObject *>(self));
 #endif
     with_instance_map(ptr, [&](instance_map &instances) { instances.emplace(ptr, self); });
     return true; // unused, but gives the same signature as the deregister func
 }
 inline bool deregister_instance_impl(void *ptr, instance *self) {
     assert(ptr);
     return with_instance_map(ptr, [&](instance_map &instances) {
         auto range = instances.equal_range(ptr);
         for (auto it = range.first; it != range.second; ++it) {
             if (self == it->second) {
                 instances.erase(it);
                 return true;
             }
         }
         return false;
     });
 }
 
 inline void register_instance(instance *self, void *valptr, const type_info *tinfo) {
     register_instance_impl(valptr, self);
     if (!tinfo->simple_ancestors) {
         traverse_offset_bases(valptr, tinfo, self, register_instance_impl);
     }
 }
 
 inline bool deregister_instance(instance *self, void *valptr, const type_info *tinfo) {
     bool ret = deregister_instance_impl(valptr, self);
     if (!tinfo->simple_ancestors) {
         traverse_offset_bases(valptr, tinfo, self, deregister_instance_impl);
     }
     return ret;
 }
 
 /// Instance creation function for all pybind11 types. It allocates the internal instance layout
 /// for holding C++ objects and holders.  Allocation is done lazily (the first time the instance is
 /// cast to a reference or pointer), and initialization is done by an `__init__` function.
 inline PyObject *make_new_instance(PyTypeObject *type) {
 #if defined(PYPY_VERSION)
     // PyPy gets tp_basicsize wrong (issue 2482) under multiple inheritance when the first
     // inherited object is a plain Python type (i.e. not derived from an extension type).  Fix it.
     ssize_t instance_size = static_cast<ssize_t>(sizeof(instance));
     if (type->tp_basicsize < instance_size) {
         type->tp_basicsize = instance_size;
     }
 #endif
     PyObject *self = type->tp_alloc(type, 0);
     auto *inst = reinterpret_cast<instance *>(self);
     // Allocate the value/holder internals:
     inst->allocate_layout();
 
     return self;
 }
 
 /// Instance creation function for all pybind11 types. It only allocates space for the
 /// C++ object, but doesn't call the constructor -- an `__init__` function must do that.
 extern "C" inline PyObject *pybind11_object_new(PyTypeObject *type, PyObject *, PyObject *) {
     return make_new_instance(type);
 }
 
 /// An `__init__` function constructs the C++ object. Users should provide at least one
 /// of these using `py::init` or directly with `.def(__init__, ...)`. Otherwise, the
 /// following default function will be used which simply throws an exception.
 extern "C" inline int pybind11_object_init(PyObject *self, PyObject *, PyObject *) {
     PyTypeObject *type = Py_TYPE(self);
     std::string msg = get_fully_qualified_tp_name(type) + ": No constructor defined!";
     set_error(PyExc_TypeError, msg.c_str());
     return -1;
 }
 
 inline void add_patient(PyObject *nurse, PyObject *patient) {
     auto *instance = reinterpret_cast<detail::instance *>(nurse);
     instance->has_patients = true;
     Py_INCREF(patient);
 
     with_internals([&](internals &internals) { internals.patients[nurse].push_back(patient); });
 }
 
 inline void clear_patients(PyObject *self) {
     auto *instance = reinterpret_cast<detail::instance *>(self);
     std::vector<PyObject *> patients;
 
     with_internals([&](internals &internals) {
         auto pos = internals.patients.find(self);
 
         if (pos == internals.patients.end()) {
             pybind11_fail(
                 "FATAL: Internal consistency check failed: Invalid clear_patients() call.");
         }
 
         // Clearing the patients can cause more Python code to run, which
         // can invalidate the iterator. Extract the vector of patients
         // from the unordered_map first.
         patients = std::move(pos->second);
         internals.patients.erase(pos);
     });
 
     instance->has_patients = false;
     for (PyObject *&patient : patients) {
         Py_CLEAR(patient);
     }
 }
 
 /// Clears all internal data from the instance and removes it from registered instances in
 /// preparation for deallocation.
 inline void clear_instance(PyObject *self) {
     auto *instance = reinterpret_cast<detail::instance *>(self);
 
     // Deallocate any values/holders, if present:
     for (auto &v_h : values_and_holders(instance)) {
         if (v_h) {
 
             // We have to deregister before we call dealloc because, for virtual MI types, we still
             // need to be able to get the parent pointers.
             if (v_h.instance_registered()
                 && !deregister_instance(instance, v_h.value_ptr(), v_h.type)) {
                 pybind11_fail(
                     "pybind11_object_dealloc(): Tried to deallocate unregistered instance!");
             }
 
             if (instance->owned || v_h.holder_constructed()) {
                 v_h.type->dealloc(v_h);
             }
         } else if (v_h.holder_constructed()) {
             v_h.type->dealloc(v_h); // Disowned instance.
         }
     }
     // Deallocate the value/holder layout internals:
     instance->deallocate_layout();
 
     if (instance->weakrefs) {
         PyObject_ClearWeakRefs(self);
     }
 
     PyObject **dict_ptr = _PyObject_GetDictPtr(self);
     if (dict_ptr) {
         Py_CLEAR(*dict_ptr);
     }
 
     if (instance->has_patients) {
         clear_patients(self);
     }
 }
 
 /// Instance destructor function for all pybind11 types. It calls `type_info.dealloc`
 /// to destroy the C++ object itself, while the rest is Python bookkeeping.
 extern "C" inline void pybind11_object_dealloc(PyObject *self) {
     auto *type = Py_TYPE(self);
 
     // If this is a GC tracked object, untrack it first
     // Note that the track call is implicitly done by the
     // default tp_alloc, which we never override.
     if (PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC) != 0) {
         PyObject_GC_UnTrack(self);
     }
 
     clear_instance(self);
 
     type->tp_free(self);
 
     // This was not needed before Python 3.8 (Python issue 35810)
     // https://github.com/pybind/pybind11/issues/1946
     Py_DECREF(type);
 }
 
 PYBIND11_WARNING_PUSH
 PYBIND11_WARNING_DISABLE_GCC("-Wredundant-decls")
 
 std::string error_string();
 
 PYBIND11_WARNING_POP
 
 /** Create the type which can be used as a common base for all classes.  This is
     needed in order to satisfy Python's requirements for multiple inheritance.
     Return value: New reference. */
 inline PyObject *make_object_base_type(PyTypeObject *metaclass) {
     constexpr auto *name = "pybind11_object";
     auto name_obj = reinterpret_steal<object>(PYBIND11_FROM_STRING(name));
 
     /* Danger zone: from now (and until PyType_Ready), make sure to
        issue no Python C API calls which could potentially invoke the
        garbage collector (the GC will call type_traverse(), which will in
        turn find the newly constructed type in an invalid state) */
     auto *heap_type = reinterpret_cast<PyHeapTypeObject *>(metaclass->tp_alloc(metaclass, 0));
     if (!heap_type) {
         pybind11_fail("make_object_base_type(): error allocating type!");
     }
 
     heap_type->ht_name = name_obj.inc_ref().ptr();
 #ifdef PYBIND11_BUILTIN_QUALNAME
     heap_type->ht_qualname = name_obj.inc_ref().ptr();
 #endif
 
     auto *type = &heap_type->ht_type;
     type->tp_name = name;
     type->tp_base = type_incref(&PyBaseObject_Type);
     type->tp_basicsize = static_cast<ssize_t>(sizeof(instance));
     type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HEAPTYPE;
 
     type->tp_new = pybind11_object_new;
     type->tp_init = pybind11_object_init;
     type->tp_dealloc = pybind11_object_dealloc;
 
     /* Support weak references (needed for the keep_alive feature) */
     type->tp_weaklistoffset = offsetof(instance, weakrefs);
 
     if (PyType_Ready(type) < 0) {
         pybind11_fail("PyType_Ready failed in make_object_base_type(): " + error_string());
     }
 
     setattr(reinterpret_cast<PyObject *>(type), "__module__", str(PYBIND11_DUMMY_MODULE_NAME));
     PYBIND11_SET_OLDPY_QUALNAME(type, name_obj);
 
     assert(!PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC));
     return reinterpret_cast<PyObject *>(heap_type);
 }
 
 /// dynamic_attr: Allow the garbage collector to traverse the internal instance `__dict__`.
 extern "C" inline int pybind11_traverse(PyObject *self, visitproc visit, void *arg) {
 #if PY_VERSION_HEX >= 0x030D0000
     PyObject_VisitManagedDict(self, visit, arg);
 #else
     PyObject *&dict = *_PyObject_GetDictPtr(self);
     Py_VISIT(dict);
 #endif
 // https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_traverse
 #if PY_VERSION_HEX >= 0x03090000
     Py_VISIT(Py_TYPE(self));
 #endif
     return 0;
 }
 
 /// dynamic_attr: Allow the GC to clear the dictionary.
 extern "C" inline int pybind11_clear(PyObject *self) {
 #if PY_VERSION_HEX >= 0x030D0000
     PyObject_ClearManagedDict(self);
 #else
     PyObject *&dict = *_PyObject_GetDictPtr(self);
     Py_CLEAR(dict);
 #endif
     return 0;
 }
 
 /// Give instances of this type a `__dict__` and opt into garbage collection.
 inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type) {
     auto *type = &heap_type->ht_type;
     type->tp_flags |= Py_TPFLAGS_HAVE_GC;
 #ifdef PYBIND11_BACKWARD_COMPATIBILITY_TP_DICTOFFSET
     type->tp_dictoffset = type->tp_basicsize;           // place dict at the end
     type->tp_basicsize += (ssize_t) sizeof(PyObject *); // and allocate enough space for it
 #else
     type->tp_flags |= Py_TPFLAGS_MANAGED_DICT;
 #endif
     type->tp_traverse = pybind11_traverse;
     type->tp_clear = pybind11_clear;
 
     static PyGetSetDef getset[]
         = {{"__dict__", PyObject_GenericGetDict, PyObject_GenericSetDict, nullptr, nullptr},
            {nullptr, nullptr, nullptr, nullptr, nullptr}};
     type->tp_getset = getset;
 }
 
 /// buffer_protocol: Fill in the view as specified by flags.
 extern "C" inline int pybind11_getbuffer(PyObject *obj, Py_buffer *view, int flags) {
     // Look for a `get_buffer` implementation in this type's info or any bases (following MRO).
     type_info *tinfo = nullptr;
     for (auto type : reinterpret_borrow<tuple>(Py_TYPE(obj)->tp_mro)) {
         tinfo = get_type_info((PyTypeObject *) type.ptr());
         if (tinfo && tinfo->get_buffer) {
             break;
         }
     }
     if (view == nullptr || !tinfo || !tinfo->get_buffer) {
         if (view) {
             view->obj = nullptr;
         }
         set_error(PyExc_BufferError, "pybind11_getbuffer(): Internal error");
         return -1;
     }
     std::memset(view, 0, sizeof(Py_buffer));
     std::unique_ptr<buffer_info> info = nullptr;
     try {
         info.reset(tinfo->get_buffer(obj, tinfo->get_buffer_data));
     } catch (...) {
         try_translate_exceptions();
         raise_from(PyExc_BufferError, "Error getting buffer");
         return -1;
     }
     if (info == nullptr) {
         pybind11_fail("FATAL UNEXPECTED SITUATION: tinfo->get_buffer() returned nullptr.");
     }
 
     if ((flags & PyBUF_WRITABLE) == PyBUF_WRITABLE && info->readonly) {
         // view->obj = nullptr;  // Was just memset to 0, so not necessary
         set_error(PyExc_BufferError, "Writable buffer requested for readonly storage");
         return -1;
     }
 
     // Fill in all the information, and then downgrade as requested by the caller, or raise an
     // error if that's not possible.
     view->itemsize = info->itemsize;
     view->len = view->itemsize;
     for (auto s : info->shape) {
         view->len *= s;
     }
     view->ndim = static_cast<int>(info->ndim);
     view->shape = info->shape.data();
     view->strides = info->strides.data();
     view->readonly = static_cast<int>(info->readonly);
     if ((flags & PyBUF_FORMAT) == PyBUF_FORMAT) {
         view->format = const_cast<char *>(info->format.c_str());
     }
 
     // Note, all contiguity flags imply PyBUF_STRIDES and lower.
     if ((flags & PyBUF_C_CONTIGUOUS) == PyBUF_C_CONTIGUOUS) {
         if (PyBuffer_IsContiguous(view, 'C') == 0) {
             std::memset(view, 0, sizeof(Py_buffer));
             set_error(PyExc_BufferError,
                       "C-contiguous buffer requested for discontiguous storage");
             return -1;
         }
     } else if ((flags & PyBUF_F_CONTIGUOUS) == PyBUF_F_CONTIGUOUS) {
         if (PyBuffer_IsContiguous(view, 'F') == 0) {
             std::memset(view, 0, sizeof(Py_buffer));
             set_error(PyExc_BufferError,
                       "Fortran-contiguous buffer requested for discontiguous storage");
             return -1;
         }
     } else if ((flags & PyBUF_ANY_CONTIGUOUS) == PyBUF_ANY_CONTIGUOUS) {
         if (PyBuffer_IsContiguous(view, 'A') == 0) {
             std::memset(view, 0, sizeof(Py_buffer));
             set_error(PyExc_BufferError, "Contiguous buffer requested for discontiguous storage");
             return -1;
         }
 
     } else if ((flags & PyBUF_STRIDES) != PyBUF_STRIDES) {
         // If no strides are requested, the buffer must be C-contiguous.
         // https://docs.python.org/3/c-api/buffer.html#contiguity-requests
         if (PyBuffer_IsContiguous(view, 'C') == 0) {
             std::memset(view, 0, sizeof(Py_buffer));
             set_error(PyExc_BufferError,
                       "C-contiguous buffer requested for discontiguous storage");
             return -1;
         }
 
         view->strides = nullptr;
 
         // Since this is a contiguous buffer, it can also pretend to be 1D.
         if ((flags & PyBUF_ND) != PyBUF_ND) {
             view->shape = nullptr;
             view->ndim = 0;
         }
     }
 
     // Set these after all checks so they don't leak out into the caller, and can be automatically
     // cleaned up on error.
     view->buf = info->ptr;
     view->internal = info.release();
     view->obj = obj;
     Py_INCREF(view->obj);
     return 0;
 }
 
 /// buffer_protocol: Release the resources of the buffer.
 extern "C" inline void pybind11_releasebuffer(PyObject *, Py_buffer *view) {
     delete (buffer_info *) view->internal;
 }
 
 /// Give this type a buffer interface.
 inline void enable_buffer_protocol(PyHeapTypeObject *heap_type) {
     heap_type->ht_type.tp_as_buffer = &heap_type->as_buffer;
 
     heap_type->as_buffer.bf_getbuffer = pybind11_getbuffer;
     heap_type->as_buffer.bf_releasebuffer = pybind11_releasebuffer;
 }
 
 /** Create a brand new Python type according to the `type_record` specification.
     Return value: New reference. */
 inline PyObject *make_new_python_type(const type_record &rec) {
     auto name = reinterpret_steal<object>(PYBIND11_FROM_STRING(rec.name));
 
     auto qualname = name;
     if (rec.scope && !PyModule_Check(rec.scope.ptr()) && hasattr(rec.scope, "__qualname__")) {
         qualname = reinterpret_steal<object>(
             PyUnicode_FromFormat("%U.%U", rec.scope.attr("__qualname__").ptr(), name.ptr()));
     }
 
     object module_ = get_module_name_if_available(rec.scope);
     const auto *full_name = c_str(
 #if !defined(PYPY_VERSION)
         module_ ? str(module_).cast<std::string>() + "." + rec.name :
 #endif
                 rec.name);
 
     char *tp_doc = nullptr;
     if (rec.doc && options::show_user_defined_docstrings()) {
         /* Allocate memory for docstring (Python will free this later on) */
         size_t size = std::strlen(rec.doc) + 1;
 #if PY_VERSION_HEX >= 0x030D0000
         tp_doc = static_cast<char *>(PyMem_MALLOC(size));
 #else
         tp_doc = (char *) PyObject_MALLOC(size);
 #endif
         std::memcpy((void *) tp_doc, rec.doc, size);
     }
 
     auto &internals = get_internals();
     auto bases = tuple(rec.bases);
     auto *base = (bases.empty()) ? internals.instance_base : bases[0].ptr();
 
     /* Danger zone: from now (and until PyType_Ready), make sure to
        issue no Python C API calls which could potentially invoke the
        garbage collector (the GC will call type_traverse(), which will in
        turn find the newly constructed type in an invalid state) */
     auto *metaclass = rec.metaclass.ptr() ? reinterpret_cast<PyTypeObject *>(rec.metaclass.ptr())
                                           : internals.default_metaclass;
 
     auto *heap_type = reinterpret_cast<PyHeapTypeObject *>(metaclass->tp_alloc(metaclass, 0));
     if (!heap_type) {
         pybind11_fail(std::string(rec.name) + ": Unable to create type object!");
     }
 
     heap_type->ht_name = name.release().ptr();
 #ifdef PYBIND11_BUILTIN_QUALNAME
     heap_type->ht_qualname = qualname.inc_ref().ptr();
 #endif
 
     auto *type = &heap_type->ht_type;
     type->tp_name = full_name;
     type->tp_doc = tp_doc;
     type->tp_base = type_incref(reinterpret_cast<PyTypeObject *>(base));
     type->tp_basicsize = static_cast<ssize_t>(sizeof(instance));
     if (!bases.empty()) {
         type->tp_bases = bases.release().ptr();
     }
 
     /* Don't inherit base __init__ */
     type->tp_init = pybind11_object_init;
 
     /* Supported protocols */
     type->tp_as_number = &heap_type->as_number;
     type->tp_as_sequence = &heap_type->as_sequence;
     type->tp_as_mapping = &heap_type->as_mapping;
     type->tp_as_async = &heap_type->as_async;
 
     /* Flags */
     type->tp_flags |= Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HEAPTYPE;
     if (!rec.is_final) {
         type->tp_flags |= Py_TPFLAGS_BASETYPE;
     }
 
     if (rec.dynamic_attr) {
         enable_dynamic_attributes(heap_type);
     }
 
     if (rec.buffer_protocol) {
         enable_buffer_protocol(heap_type);
     }
 
     if (rec.custom_type_setup_callback) {
         rec.custom_type_setup_callback(heap_type);
     }
 
     if (PyType_Ready(type) < 0) {
         pybind11_fail(std::string(rec.name) + ": PyType_Ready failed: " + error_string());
     }
 
     assert(!rec.dynamic_attr || PyType_HasFeature(type, Py_TPFLAGS_HAVE_GC));
 
     /* Register type with the parent scope */
     if (rec.scope) {
         setattr(rec.scope, rec.name, reinterpret_cast<PyObject *>(type));
     } else {
         Py_INCREF(type); // Keep it alive forever (reference leak)
     }
 
     if (module_) { // Needed by pydoc
         setattr(reinterpret_cast<PyObject *>(type), "__module__", module_);
     }
 
     PYBIND11_SET_OLDPY_QUALNAME(type, qualname);
 
     return reinterpret_cast<PyObject *>(type);
 }
 
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)

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