pybind11::detail::instance Struct Reference

The 'instance' type which needs to be standard layout (need to be able to use 'offsetof') More...

#include <common.h>

Public Member Functions
void	allocate_layout ()
	Initializes all of the above type/values/holders data (but not the instance values themselves)
void	deallocate_layout ()
	Destroys/deallocates all of the above.
value_and_holder	get_value_and_holder (const type_info *find_type=nullptr, bool throw_if_missing=true)

Public Attributes
union {
void *   simple_value_holder [1+instance_simple_holder_in_ptrs()]
nonsimple_values_and_holders   nonsimple
};
	Storage for pointers and holder; see simple_layout, below, for a description.
PyObject *	weakrefs
	Weak references.
bool	owned: 1
	If true, the pointer is owned which means we're free to manage it with a holder.
bool	simple_layout: 1
bool	simple_holder_constructed: 1
	For simple layout, tracks whether the holder has been constructed.
bool	simple_instance_registered: 1
	For simple layout, tracks whether the instance is registered in registered_instances
bool	has_patients: 1
	If true, get_internals().patients has an entry for this object.

Static Public Attributes
static constexpr uint8_t	status_holder_constructed = 1
	Bit values for the non-simple status flags.
static constexpr uint8_t	status_instance_registered = 2

Detailed Description

The 'instance' type which needs to be standard layout (need to be able to use 'offsetof')

Member Function Documentation

get_value_and_holder()

value_and_holder pybind11::detail::instance::get_value_and_holder	(	const type_info *	find_type = nullptr,
		bool	throw_if_missing = true
	)

Returns the value_and_holder wrapper for the given type (or the first, if find_type omitted). Returns a default-constructed (with .inst = nullptr) object on failure if throw_if_missing is false.

Member Data Documentation

simple_layout

bool pybind11::detail::instance::simple_layout

An instance has two possible value/holder layouts.

Simple layout (when this flag is true), means the simple_value_holder is set with a pointer and the holder object governing that pointer, i.e. [val1*][holder]. This layout is applied whenever there is no python-side multiple inheritance of bound C++ types and the type's holder will fit in the default space (which is large enough to hold either a std::unique_ptr or std::shared_ptr).

Non-simple layout applies when using custom holders that require more space than shared_ptr (which is typically the size of two pointers), or when multiple inheritance is used on the python side. Non-simple layout allocates the required amount of memory to have multiple bound C++ classes as parents. Under this layout, nonsimple.values_and_holders is set to a pointer to allocated space of the required space to hold a sequence of value pointers and holders followed status, a set of bit flags (1 byte each), i.e. [val1*][holder1][val2*][holder2]...[bb...] where each [block] is rounded up to a multiple of sizeof(void *). nonsimple.status is, for convenience, a pointer to the beginning of the [bb...] block (but not independently allocated).

Status bits indicate whether the associated holder is constructed (& status_holder_constructed) and whether the value pointer is registered (& status_instance_registered) in registered_instances.

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The documentation for this struct was generated from the following file:

• third_party/pybind11/include/pybind11/detail/common.h