blob: 00ce1a7a1ec8e9a9798fb175836130c2e8b90893 [file] [log] [blame]
pybind11/detail/type_caster_base.h (originally first part of pybind11/cast.h)
Copyright (c) 2016 Wenzel Jakob <>
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 "../pytypes.h"
#include "common.h"
#include "descr.h"
#include "internals.h"
#include "typeid.h"
#include <cstdint>
#include <iterator>
#include <new>
#include <string>
#include <type_traits>
#include <typeindex>
#include <typeinfo>
#include <unordered_map>
#include <utility>
#include <vector>
/// A life support system for temporary objects created by `type_caster::load()`.
/// Adding a patient will keep it alive up until the enclosing function returns.
class loader_life_support {
loader_life_support* parent = nullptr;
std::unordered_set<PyObject *> keep_alive;
#if defined(WITH_THREAD)
// Store stack pointer in thread-local storage.
static PYBIND11_TLS_KEY_REF get_stack_tls_key() {
return get_local_internals().loader_life_support_tls_key;
# else
return get_internals().loader_life_support_tls_key;
# endif
static loader_life_support *get_stack_top() {
return static_cast<loader_life_support *>(PYBIND11_TLS_GET_VALUE(get_stack_tls_key()));
static void set_stack_top(loader_life_support *value) {
PYBIND11_TLS_REPLACE_VALUE(get_stack_tls_key(), value);
// Use single global variable for stack.
static loader_life_support **get_stack_pp() {
static loader_life_support *global_stack = nullptr;
return global_stack;
static loader_life_support *get_stack_top() { return *get_stack_pp(); }
static void set_stack_top(loader_life_support *value) { *get_stack_pp() = value; }
/// A new patient frame is created when a function is entered
loader_life_support() {
parent = get_stack_top();
/// ... and destroyed after it returns
~loader_life_support() {
if (get_stack_top() != this)
pybind11_fail("loader_life_support: internal error");
for (auto* item : keep_alive)
/// This can only be used inside a pybind11-bound function, either by `argument_loader`
/// at argument preparation time or by `py::cast()` at execution time.
PYBIND11_NOINLINE static void add_patient(handle h) {
loader_life_support *frame = get_stack_top();
if (!frame) {
// NOTE: It would be nice to include the stack frames here, as this indicates
// use of pybind11::cast<> outside the normal call framework, finding such
// a location is challenging. Developers could consider printing out
// stack frame addresses here using something like __builtin_frame_address(0)
throw cast_error("When called outside a bound function, py::cast() cannot "
"do Python -> C++ conversions which require the creation "
"of temporary values");
if (frame->keep_alive.insert(h.ptr()).second)
// Gets the cache entry for the given type, creating it if necessary. The return value is the pair
// returned by emplace, i.e. an iterator for the entry and a bool set to `true` if the entry was
// just created.
inline std::pair<decltype(internals::registered_types_py)::iterator, bool> all_type_info_get_cache(PyTypeObject *type);
// Populates a just-created cache entry.
PYBIND11_NOINLINE void all_type_info_populate(PyTypeObject *t, std::vector<type_info *> &bases) {
std::vector<PyTypeObject *> check;
for (handle parent : reinterpret_borrow<tuple>(t->tp_bases))
check.push_back((PyTypeObject *) parent.ptr());
auto const &type_dict = get_internals().registered_types_py;
for (size_t i = 0; i < check.size(); i++) {
auto type = check[i];
// Ignore Python2 old-style class super type:
if (!PyType_Check((PyObject *) type)) continue;
// Check `type` in the current set of registered python types:
auto it = type_dict.find(type);
if (it != type_dict.end()) {
// We found a cache entry for it, so it's either pybind-registered or has pre-computed
// pybind bases, but we have to make sure we haven't already seen the type(s) before: we
// want to follow Python/virtual C++ rules that there should only be one instance of a
// common base.
for (auto *tinfo : it->second) {
// NB: Could use a second set here, rather than doing a linear search, but since
// having a large number of immediate pybind11-registered types seems fairly
// unlikely, that probably isn't worthwhile.
bool found = false;
for (auto *known : bases) {
if (known == tinfo) { found = true; break; }
if (!found) bases.push_back(tinfo);
else if (type->tp_bases) {
// It's some python type, so keep follow its bases classes to look for one or more
// registered types
if (i + 1 == check.size()) {
// When we're at the end, we can pop off the current element to avoid growing
// `check` when adding just one base (which is typical--i.e. when there is no
// multiple inheritance)
for (handle parent : reinterpret_borrow<tuple>(type->tp_bases))
check.push_back((PyTypeObject *) parent.ptr());
* Extracts vector of type_info pointers of pybind-registered roots of the given Python type. Will
* be just 1 pybind type for the Python type of a pybind-registered class, or for any Python-side
* derived class that uses single inheritance. Will contain as many types as required for a Python
* class that uses multiple inheritance to inherit (directly or indirectly) from multiple
* pybind-registered classes. Will be empty if neither the type nor any base classes are
* pybind-registered.
* The value is cached for the lifetime of the Python type.
inline const std::vector<detail::type_info *> &all_type_info(PyTypeObject *type) {
auto ins = all_type_info_get_cache(type);
if (ins.second)
// New cache entry: populate it
all_type_info_populate(type, ins.first->second);
return ins.first->second;
* Gets a single pybind11 type info for a python type. Returns nullptr if neither the type nor any
* ancestors are pybind11-registered. Throws an exception if there are multiple bases--use
* `all_type_info` instead if you want to support multiple bases.
PYBIND11_NOINLINE detail::type_info* get_type_info(PyTypeObject *type) {
auto &bases = all_type_info(type);
if (bases.empty())
return nullptr;
if (bases.size() > 1)
pybind11_fail("pybind11::detail::get_type_info: type has multiple pybind11-registered bases");
return bases.front();
inline detail::type_info *get_local_type_info(const std::type_index &tp) {
auto &locals = get_local_internals().registered_types_cpp;
auto it = locals.find(tp);
if (it != locals.end())
return it->second;
return nullptr;
inline detail::type_info *get_global_type_info(const std::type_index &tp) {
auto &types = get_internals().registered_types_cpp;
auto it = types.find(tp);
if (it != types.end())
return it->second;
return nullptr;
/// Return the type info for a given C++ type; on lookup failure can either throw or return nullptr.
PYBIND11_NOINLINE detail::type_info *get_type_info(const std::type_index &tp,
bool throw_if_missing = false) {
if (auto ltype = get_local_type_info(tp))
return ltype;
if (auto gtype = get_global_type_info(tp))
return gtype;
if (throw_if_missing) {
std::string tname =;
pybind11_fail("pybind11::detail::get_type_info: unable to find type info for \"" + tname + "\"");
return nullptr;
PYBIND11_NOINLINE handle get_type_handle(const std::type_info &tp, bool throw_if_missing) {
detail::type_info *type_info = get_type_info(tp, throw_if_missing);
return handle(type_info ? ((PyObject *) type_info->type) : nullptr);
// Searches the inheritance graph for a registered Python instance, using all_type_info().
PYBIND11_NOINLINE handle find_registered_python_instance(void *src,
const detail::type_info *tinfo) {
auto it_instances = get_internals().registered_instances.equal_range(src);
for (auto it_i = it_instances.first; it_i != it_instances.second; ++it_i) {
for (auto instance_type : detail::all_type_info(Py_TYPE(it_i->second))) {
if (instance_type && same_type(*instance_type->cpptype, *tinfo->cpptype))
return handle((PyObject *) it_i->second).inc_ref();
return handle();
struct value_and_holder {
instance *inst = nullptr;
size_t index = 0u;
const detail::type_info *type = nullptr;
void **vh = nullptr;
// Main constructor for a found value/holder:
value_and_holder(instance *i, const detail::type_info *type, size_t vpos, size_t index) :
inst{i}, index{index}, type{type},
vh{inst->simple_layout ? inst->simple_value_holder : &inst->nonsimple.values_and_holders[vpos]}
// Default constructor (used to signal a value-and-holder not found by get_value_and_holder())
value_and_holder() = default;
// Used for past-the-end iterator
explicit value_and_holder(size_t index) : index{index} {}
template <typename V = void> V *&value_ptr() const {
return reinterpret_cast<V *&>(vh[0]);
// True if this `value_and_holder` has a non-null value pointer
explicit operator bool() const { return value_ptr() != nullptr; }
template <typename H> H &holder() const {
return reinterpret_cast<H &>(vh[1]);
bool holder_constructed() const {
return inst->simple_layout
? inst->simple_holder_constructed
: (inst->nonsimple.status[index] & instance::status_holder_constructed) != 0u;
// NOLINTNEXTLINE(readability-make-member-function-const)
void set_holder_constructed(bool v = true) {
if (inst->simple_layout)
inst->simple_holder_constructed = v;
else if (v)
inst->nonsimple.status[index] |= instance::status_holder_constructed;
inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_holder_constructed;
bool instance_registered() const {
return inst->simple_layout
? inst->simple_instance_registered
: ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
// NOLINTNEXTLINE(readability-make-member-function-const)
void set_instance_registered(bool v = true) {
if (inst->simple_layout)
inst->simple_instance_registered = v;
else if (v)
inst->nonsimple.status[index] |= instance::status_instance_registered;
inst->nonsimple.status[index] &= (std::uint8_t) ~instance::status_instance_registered;
// Container for accessing and iterating over an instance's values/holders
struct values_and_holders {
instance *inst;
using type_vec = std::vector<detail::type_info *>;
const type_vec &tinfo;
explicit values_and_holders(instance *inst)
: inst{inst}, tinfo(all_type_info(Py_TYPE(inst))) {}
struct iterator {
instance *inst = nullptr;
const type_vec *types = nullptr;
value_and_holder curr;
friend struct values_and_holders;
iterator(instance *inst, const type_vec *tinfo)
: inst{inst}, types{tinfo},
curr(inst /* instance */,
types->empty() ? nullptr : (*types)[0] /* type info */,
0, /* vpos: (non-simple types only): the first vptr comes first */
0 /* index */)
// Past-the-end iterator:
explicit iterator(size_t end) : curr(end) {}
bool operator==(const iterator &other) const { return curr.index == other.curr.index; }
bool operator!=(const iterator &other) const { return curr.index != other.curr.index; }
iterator &operator++() {
if (!inst->simple_layout)
curr.vh += 1 + (*types)[curr.index]->holder_size_in_ptrs;
curr.type = curr.index < types->size() ? (*types)[curr.index] : nullptr;
return *this;
value_and_holder &operator*() { return curr; }
value_and_holder *operator->() { return &curr; }
iterator begin() { return iterator(inst, &tinfo); }
iterator end() { return iterator(tinfo.size()); }
iterator find(const type_info *find_type) {
auto it = begin(), endit = end();
while (it != endit && it->type != find_type) ++it;
return it;
size_t size() { return tinfo.size(); }
* Extracts C++ value and holder pointer references from an instance (which may contain multiple
* values/holders for python-side multiple inheritance) that match the given type. Throws an error
* if the given type (or ValueType, if omitted) is not a pybind11 base of the given instance. If
* `find_type` is omitted (or explicitly specified as nullptr) the first value/holder are returned,
* regardless of type (and the resulting .type will be nullptr).
* The returned object should be short-lived: in particular, it must not outlive the called-upon
* instance.
PYBIND11_NOINLINE value_and_holder instance::get_value_and_holder(const type_info *find_type /*= nullptr default in common.h*/, bool throw_if_missing /*= true in common.h*/) {
// Optimize common case:
if (!find_type || Py_TYPE(this) == find_type->type)
return value_and_holder(this, find_type, 0, 0);
detail::values_and_holders vhs(this);
auto it = vhs.find(find_type);
if (it != vhs.end())
return *it;
if (!throw_if_missing)
return value_and_holder();
#if defined(NDEBUG)
pybind11_fail("pybind11::detail::instance::get_value_and_holder: "
"type is not a pybind11 base of the given instance "
"(compile in debug mode for type details)");
pybind11_fail("pybind11::detail::instance::get_value_and_holder: `" +
get_fully_qualified_tp_name(find_type->type) + "' is not a pybind11 base of the given `" +
get_fully_qualified_tp_name(Py_TYPE(this)) + "' instance");
PYBIND11_NOINLINE void instance::allocate_layout() {
auto &tinfo = all_type_info(Py_TYPE(this));
const size_t n_types = tinfo.size();
if (n_types == 0)
pybind11_fail("instance allocation failed: new instance has no pybind11-registered base types");
simple_layout =
n_types == 1 && tinfo.front()->holder_size_in_ptrs <= instance_simple_holder_in_ptrs();
// Simple path: no python-side multiple inheritance, and a small-enough holder
if (simple_layout) {
simple_value_holder[0] = nullptr;
simple_holder_constructed = false;
simple_instance_registered = false;
else { // multiple base types or a too-large holder
// Allocate space to hold: [v1*][h1][v2*][h2]...[bb...] where [vN*] is a value pointer,
// [hN] is the (uninitialized) holder instance for value N, and [bb...] is a set of bool
// values that tracks whether each associated holder has been initialized. Each [block] is
// padded, if necessary, to an integer multiple of sizeof(void *).
size_t space = 0;
for (auto t : tinfo) {
space += 1; // value pointer
space += t->holder_size_in_ptrs; // holder instance
size_t flags_at = space;
space += size_in_ptrs(n_types); // status bytes (holder_constructed and instance_registered)
// Allocate space for flags, values, and holders, and initialize it to 0 (flags and values,
// in particular, need to be 0). Use Python's memory allocation functions: in Python 3.6
// they default to using pymalloc, which is designed to be efficient for small allocations
// like the one we're doing here; in earlier versions (and for larger allocations) they are
// just wrappers around malloc.
#if PY_VERSION_HEX >= 0x03050000
nonsimple.values_and_holders = (void **) PyMem_Calloc(space, sizeof(void *));
if (!nonsimple.values_and_holders) throw std::bad_alloc();
nonsimple.values_and_holders = (void **) PyMem_New(void *, space);
if (!nonsimple.values_and_holders) throw std::bad_alloc();
std::memset(nonsimple.values_and_holders, 0, space * sizeof(void *));
nonsimple.status = reinterpret_cast<std::uint8_t *>(&nonsimple.values_and_holders[flags_at]);
owned = true;
// NOLINTNEXTLINE(readability-make-member-function-const)
PYBIND11_NOINLINE void instance::deallocate_layout() {
if (!simple_layout)
PYBIND11_NOINLINE bool isinstance_generic(handle obj, const std::type_info &tp) {
handle type = detail::get_type_handle(tp, false);
if (!type)
return false;
return isinstance(obj, type);
PYBIND11_NOINLINE std::string error_string() {
if (!PyErr_Occurred()) {
PyErr_SetString(PyExc_RuntimeError, "Unknown internal error occurred");
return "Unknown internal error occurred";
error_scope scope; // Preserve error state
std::string errorString;
if (scope.type) {
errorString += handle(scope.type).attr("__name__").cast<std::string>();
errorString += ": ";
if (scope.value)
errorString += (std::string) str(scope.value);
PyErr_NormalizeException(&scope.type, &scope.value, &scope.trace);
if (scope.trace != nullptr)
PyException_SetTraceback(scope.value, scope.trace);
#if !defined(PYPY_VERSION)
if (scope.trace) {
auto *trace = (PyTracebackObject *) scope.trace;
/* Get the deepest trace possible */
while (trace->tb_next)
trace = trace->tb_next;
PyFrameObject *frame = trace->tb_frame;
errorString += "\n\nAt:\n";
while (frame) {
#if PY_VERSION_HEX >= 0x03090000
PyCodeObject *f_code = PyFrame_GetCode(frame);
PyCodeObject *f_code = frame->f_code;
int lineno = PyFrame_GetLineNumber(frame);
errorString +=
" " + handle(f_code->co_filename).cast<std::string>() +
"(" + std::to_string(lineno) + "): " +
handle(f_code->co_name).cast<std::string>() + "\n";
frame = frame->f_back;
return errorString;
PYBIND11_NOINLINE handle get_object_handle(const void *ptr, const detail::type_info *type ) {
auto &instances = get_internals().registered_instances;
auto range = instances.equal_range(ptr);
for (auto it = range.first; it != range.second; ++it) {
for (const auto &vh : values_and_holders(it->second)) {
if (vh.type == type)
return handle((PyObject *) it->second);
return handle();
inline PyThreadState *get_thread_state_unchecked() {
#if defined(PYPY_VERSION)
return PyThreadState_GET();
#elif PY_VERSION_HEX < 0x03000000
return _PyThreadState_Current;
#elif PY_VERSION_HEX < 0x03050000
return (PyThreadState*) _Py_atomic_load_relaxed(&_PyThreadState_Current);
#elif PY_VERSION_HEX < 0x03050200
return (PyThreadState*) _PyThreadState_Current.value;
return _PyThreadState_UncheckedGet();
// Forward declarations
void keep_alive_impl(handle nurse, handle patient);
inline PyObject *make_new_instance(PyTypeObject *type);
class type_caster_generic {
PYBIND11_NOINLINE explicit type_caster_generic(const std::type_info &type_info)
: typeinfo(get_type_info(type_info)), cpptype(&type_info) {}
explicit type_caster_generic(const type_info *typeinfo)
: typeinfo(typeinfo), cpptype(typeinfo ? typeinfo->cpptype : nullptr) {}
bool load(handle src, bool convert) {
return load_impl<type_caster_generic>(src, convert);
PYBIND11_NOINLINE static handle cast(const void *_src, return_value_policy policy, handle parent,
const detail::type_info *tinfo,
void *(*copy_constructor)(const void *),
void *(*move_constructor)(const void *),
const void *existing_holder = nullptr) {
if (!tinfo) // no type info: error will be set already
return handle();
void *src = const_cast<void *>(_src);
if (src == nullptr)
return none().release();
if (handle registered_inst = find_registered_python_instance(src, tinfo))
return registered_inst;
auto inst = reinterpret_steal<object>(make_new_instance(tinfo->type));
auto wrapper = reinterpret_cast<instance *>(inst.ptr());
wrapper->owned = false;
void *&valueptr = values_and_holders(wrapper).begin()->value_ptr();
switch (policy) {
case return_value_policy::automatic:
case return_value_policy::take_ownership:
valueptr = src;
wrapper->owned = true;
case return_value_policy::automatic_reference:
case return_value_policy::reference:
valueptr = src;
wrapper->owned = false;
case return_value_policy::copy:
if (copy_constructor)
valueptr = copy_constructor(src);
else {
#if defined(NDEBUG)
throw cast_error("return_value_policy = copy, but type is "
"non-copyable! (compile in debug mode for details)");
std::string type_name(tinfo->cpptype->name());
throw cast_error("return_value_policy = copy, but type " +
type_name + " is non-copyable!");
wrapper->owned = true;
case return_value_policy::move:
if (move_constructor)
valueptr = move_constructor(src);
else if (copy_constructor)
valueptr = copy_constructor(src);
else {
#if defined(NDEBUG)
throw cast_error("return_value_policy = move, but type is neither "
"movable nor copyable! "
"(compile in debug mode for details)");
std::string type_name(tinfo->cpptype->name());
throw cast_error("return_value_policy = move, but type " +
type_name + " is neither movable nor copyable!");
wrapper->owned = true;
case return_value_policy::reference_internal:
valueptr = src;
wrapper->owned = false;
keep_alive_impl(inst, parent);
throw cast_error("unhandled return_value_policy: should not happen!");
tinfo->init_instance(wrapper, existing_holder);
return inst.release();
// Base methods for generic caster; there are overridden in copyable_holder_caster
void load_value(value_and_holder &&v_h) {
auto *&vptr = v_h.value_ptr();
// Lazy allocation for unallocated values:
if (vptr == nullptr) {
auto *type = v_h.type ? v_h.type : typeinfo;
if (type->operator_new) {
vptr = type->operator_new(type->type_size);
} else {
#if defined(__cpp_aligned_new) && (!defined(_MSC_VER) || _MSC_VER >= 1912)
if (type->type_align > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
vptr = ::operator new(type->type_size,
vptr = ::operator new(type->type_size);
value = vptr;
bool try_implicit_casts(handle src, bool convert) {
for (auto &cast : typeinfo->implicit_casts) {
type_caster_generic sub_caster(*cast.first);
if (sub_caster.load(src, convert)) {
value = cast.second(sub_caster.value);
return true;
return false;
bool try_direct_conversions(handle src) {
for (auto &converter : *typeinfo->direct_conversions) {
if (converter(src.ptr(), value))
return true;
return false;
void check_holder_compat() {}
PYBIND11_NOINLINE static void *local_load(PyObject *src, const type_info *ti) {
auto caster = type_caster_generic(ti);
if (caster.load(src, false))
return caster.value;
return nullptr;
/// Try to load with foreign typeinfo, if available. Used when there is no
/// native typeinfo, or when the native one wasn't able to produce a value.
PYBIND11_NOINLINE bool try_load_foreign_module_local(handle src) {
constexpr auto *local_key = PYBIND11_MODULE_LOCAL_ID;
const auto pytype = type::handle_of(src);
if (!hasattr(pytype, local_key))
return false;
type_info *foreign_typeinfo = reinterpret_borrow<capsule>(getattr(pytype, local_key));
// Only consider this foreign loader if actually foreign and is a loader of the correct cpp type
if (foreign_typeinfo->module_local_load == &local_load
|| (cpptype && !same_type(*cpptype, *foreign_typeinfo->cpptype)))
return false;
if (auto result = foreign_typeinfo->module_local_load(src.ptr(), foreign_typeinfo)) {
value = result;
return true;
return false;
// Implementation of `load`; this takes the type of `this` so that it can dispatch the relevant
// bits of code between here and copyable_holder_caster where the two classes need different
// logic (without having to resort to virtual inheritance).
template <typename ThisT>
PYBIND11_NOINLINE bool load_impl(handle src, bool convert) {
if (!src) return false;
if (!typeinfo) return try_load_foreign_module_local(src);
auto &this_ = static_cast<ThisT &>(*this);
PyTypeObject *srctype = Py_TYPE(src.ptr());
// Case 1: If src is an exact type match for the target type then we can reinterpret_cast
// the instance's value pointer to the target type:
if (srctype == typeinfo->type) {
this_.load_value(reinterpret_cast<instance *>(src.ptr())->get_value_and_holder());
return true;
// Case 2: We have a derived class
if (PyType_IsSubtype(srctype, typeinfo->type)) {
auto &bases = all_type_info(srctype);
bool no_cpp_mi = typeinfo->simple_type;
// Case 2a: the python type is a Python-inherited derived class that inherits from just
// one simple (no MI) pybind11 class, or is an exact match, so the C++ instance is of
// the right type and we can use reinterpret_cast.
// (This is essentially the same as case 2b, but because not using multiple inheritance
// is extremely common, we handle it specially to avoid the loop iterator and type
// pointer lookup overhead)
if (bases.size() == 1 && (no_cpp_mi || bases.front()->type == typeinfo->type)) {
this_.load_value(reinterpret_cast<instance *>(src.ptr())->get_value_and_holder());
return true;
// Case 2b: the python type inherits from multiple C++ bases. Check the bases to see if
// we can find an exact match (or, for a simple C++ type, an inherited match); if so, we
// can safely reinterpret_cast to the relevant pointer.
if (bases.size() > 1) {
for (auto base : bases) {
if (no_cpp_mi ? PyType_IsSubtype(base->type, typeinfo->type) : base->type == typeinfo->type) {
this_.load_value(reinterpret_cast<instance *>(src.ptr())->get_value_and_holder(base));
return true;
// Case 2c: C++ multiple inheritance is involved and we couldn't find an exact type match
// in the registered bases, above, so try implicit casting (needed for proper C++ casting
// when MI is involved).
if (this_.try_implicit_casts(src, convert))
return true;
// Perform an implicit conversion
if (convert) {
for (auto &converter : typeinfo->implicit_conversions) {
auto temp = reinterpret_steal<object>(converter(src.ptr(), typeinfo->type));
if (load_impl<ThisT>(temp, false)) {
return true;
if (this_.try_direct_conversions(src))
return true;
// Failed to match local typeinfo. Try again with global.
if (typeinfo->module_local) {
if (auto gtype = get_global_type_info(*typeinfo->cpptype)) {
typeinfo = gtype;
return load(src, false);
// Global typeinfo has precedence over foreign module_local
if (try_load_foreign_module_local(src)) {
return true;
// Custom converters didn't take None, now we convert None to nullptr.
if (src.is_none()) {
// Defer accepting None to other overloads (if we aren't in convert mode):
if (!convert) return false;
value = nullptr;
return true;
return false;
// Called to do type lookup and wrap the pointer and type in a pair when a dynamic_cast
// isn't needed or can't be used. If the type is unknown, sets the error and returns a pair
// with .second = nullptr. (p.first = nullptr is not an error: it becomes None).
PYBIND11_NOINLINE static std::pair<const void *, const type_info *> src_and_type(
const void *src, const std::type_info &cast_type, const std::type_info *rtti_type = nullptr) {
if (auto *tpi = get_type_info(cast_type))
return {src, const_cast<const type_info *>(tpi)};
// Not found, set error:
std::string tname = rtti_type ? rtti_type->name() :;
std::string msg = "Unregistered type : " + tname;
PyErr_SetString(PyExc_TypeError, msg.c_str());
return {nullptr, nullptr};
const type_info *typeinfo = nullptr;
const std::type_info *cpptype = nullptr;
void *value = nullptr;
* Determine suitable casting operator for pointer-or-lvalue-casting type casters. The type caster
* needs to provide `operator T*()` and `operator T&()` operators.
* If the type supports moving the value away via an `operator T&&() &&` method, it should use
* `movable_cast_op_type` instead.
template <typename T>
using cast_op_type =
typename std::add_pointer<intrinsic_t<T>>::type,
typename std::add_lvalue_reference<intrinsic_t<T>>::type>;
* Determine suitable casting operator for a type caster with a movable value. Such a type caster
* needs to provide `operator T*()`, `operator T&()`, and `operator T&&() &&`. The latter will be
* called in appropriate contexts where the value can be moved rather than copied.
* These operator are automatically provided when using the PYBIND11_TYPE_CASTER macro.
template <typename T>
using movable_cast_op_type =
conditional_t<std::is_pointer<typename std::remove_reference<T>::type>::value,
typename std::add_pointer<intrinsic_t<T>>::type,
typename std::add_rvalue_reference<intrinsic_t<T>>::type,
typename std::add_lvalue_reference<intrinsic_t<T>>::type>>;
// std::is_copy_constructible isn't quite enough: it lets std::vector<T> (and similar) through when
// T is non-copyable, but code containing such a copy constructor fails to actually compile.
template <typename T, typename SFINAE = void> struct is_copy_constructible : std::is_copy_constructible<T> {};
// Specialization for types that appear to be copy constructible but also look like stl containers
// (we specifically check for: has `value_type` and `reference` with `reference = value_type&`): if
// so, copy constructability depends on whether the value_type is copy constructible.
template <typename Container> struct is_copy_constructible<Container, enable_if_t<all_of<
std::is_same<typename Container::value_type &, typename Container::reference>,
// Avoid infinite recursion
negation<std::is_same<Container, typename Container::value_type>>
>::value>> : is_copy_constructible<typename Container::value_type> {};
// Likewise for std::pair
// (after C++17 it is mandatory that the copy constructor not exist when the two types aren't themselves
// copy constructible, but this can not be relied upon when T1 or T2 are themselves containers).
template <typename T1, typename T2> struct is_copy_constructible<std::pair<T1, T2>>
: all_of<is_copy_constructible<T1>, is_copy_constructible<T2>> {};
// The same problems arise with std::is_copy_assignable, so we use the same workaround.
template <typename T, typename SFINAE = void> struct is_copy_assignable : std::is_copy_assignable<T> {};
template <typename Container> struct is_copy_assignable<Container, enable_if_t<all_of<
std::is_same<typename Container::value_type &, typename Container::reference>
>::value>> : is_copy_assignable<typename Container::value_type> {};
template <typename T1, typename T2> struct is_copy_assignable<std::pair<T1, T2>>
: all_of<is_copy_assignable<T1>, is_copy_assignable<T2>> {};
// polymorphic_type_hook<itype>::get(src, tinfo) determines whether the object pointed
// to by `src` actually is an instance of some class derived from `itype`.
// If so, it sets `tinfo` to point to the std::type_info representing that derived
// type, and returns a pointer to the start of the most-derived object of that type
// (in which `src` is a subobject; this will be the same address as `src` in most
// single inheritance cases). If not, or if `src` is nullptr, it simply returns `src`
// and leaves `tinfo` at its default value of nullptr.
// The default polymorphic_type_hook just returns src. A specialization for polymorphic
// types determines the runtime type of the passed object and adjusts the this-pointer
// appropriately via dynamic_cast<void*>. This is what enables a C++ Animal* to appear
// to Python as a Dog (if Dog inherits from Animal, Animal is polymorphic, Dog is
// registered with pybind11, and this Animal is in fact a Dog).
// You may specialize polymorphic_type_hook yourself for types that want to appear
// polymorphic to Python but do not use C++ RTTI. (This is a not uncommon pattern
// in performance-sensitive applications, used most notably in LLVM.)
// polymorphic_type_hook_base allows users to specialize polymorphic_type_hook with
// std::enable_if. User provided specializations will always have higher priority than
// the default implementation and specialization provided in polymorphic_type_hook_base.
template <typename itype, typename SFINAE = void>
struct polymorphic_type_hook_base
static const void *get(const itype *src, const std::type_info*&) { return src; }
template <typename itype>
struct polymorphic_type_hook_base<itype, detail::enable_if_t<std::is_polymorphic<itype>::value>>
static const void *get(const itype *src, const std::type_info*& type) {
type = src ? &typeid(*src) : nullptr;
return dynamic_cast<const void*>(src);
template <typename itype, typename SFINAE = void>
struct polymorphic_type_hook : public polymorphic_type_hook_base<itype> {};
/// Generic type caster for objects stored on the heap
template <typename type> class type_caster_base : public type_caster_generic {
using itype = intrinsic_t<type>;
static constexpr auto name = _<type>();
type_caster_base() : type_caster_base(typeid(type)) { }
explicit type_caster_base(const std::type_info &info) : type_caster_generic(info) { }
static handle cast(const itype &src, return_value_policy policy, handle parent) {
if (policy == return_value_policy::automatic || policy == return_value_policy::automatic_reference)
policy = return_value_policy::copy;
return cast(&src, policy, parent);
static handle cast(itype &&src, return_value_policy, handle parent) {
return cast(&src, return_value_policy::move, parent);
// Returns a (pointer, type_info) pair taking care of necessary type lookup for a
// polymorphic type (using RTTI by default, but can be overridden by specializing
// polymorphic_type_hook). If the instance isn't derived, returns the base version.
static std::pair<const void *, const type_info *> src_and_type(const itype *src) {
auto &cast_type = typeid(itype);
const std::type_info *instance_type = nullptr;
const void *vsrc = polymorphic_type_hook<itype>::get(src, instance_type);
if (instance_type && !same_type(cast_type, *instance_type)) {
// This is a base pointer to a derived type. If the derived type is registered
// with pybind11, we want to make the full derived object available.
// In the typical case where itype is polymorphic, we get the correct
// derived pointer (which may be != base pointer) by a dynamic_cast to
// most derived type. If itype is not polymorphic, we won't get here
// except via a user-provided specialization of polymorphic_type_hook,
// and the user has promised that no this-pointer adjustment is
// required in that case, so it's OK to use static_cast.
if (const auto *tpi = get_type_info(*instance_type))
return {vsrc, tpi};
// Otherwise we have either a nullptr, an `itype` pointer, or an unknown derived pointer, so
// don't do a cast
return type_caster_generic::src_and_type(src, cast_type, instance_type);
static handle cast(const itype *src, return_value_policy policy, handle parent) {
auto st = src_and_type(src);
return type_caster_generic::cast(
st.first, policy, parent, st.second,
make_copy_constructor(src), make_move_constructor(src));
static handle cast_holder(const itype *src, const void *holder) {
auto st = src_and_type(src);
return type_caster_generic::cast(
st.first, return_value_policy::take_ownership, {}, st.second,
nullptr, nullptr, holder);
template <typename T> using cast_op_type = detail::cast_op_type<T>;
// NOLINTNEXTLINE(google-explicit-constructor)
operator itype*() { return (type *) value; }
// NOLINTNEXTLINE(google-explicit-constructor)
operator itype&() { if (!value) throw reference_cast_error(); return *((itype *) value); }
using Constructor = void *(*)(const void *);
/* Only enabled when the types are {copy,move}-constructible *and* when the type
does not have a private operator new implementation. A comma operator is used in the decltype
argument to apply SFINAE to the public copy/move constructors.*/
template <typename T, typename = enable_if_t<is_copy_constructible<T>::value>>
static auto make_copy_constructor(const T *) -> decltype(new T(std::declval<const T>()), Constructor{}) {
return [](const void *arg) -> void * {
return new T(*reinterpret_cast<const T *>(arg));
template <typename T, typename = enable_if_t<std::is_move_constructible<T>::value>>
static auto make_move_constructor(const T *) -> decltype(new T(std::declval<T&&>()), Constructor{}) {
return [](const void *arg) -> void * {
return new T(std::move(*const_cast<T *>(reinterpret_cast<const T *>(arg))));
static Constructor make_copy_constructor(...) { return nullptr; }
static Constructor make_move_constructor(...) { return nullptr; }