Object handlers

Nearly all operations on objects in PHP go through object handlers and every magic method or magic interface is implemented with an object or class handler internally. Furthermore there are quite a few handlers which are not exposed to userland PHP. For example internal classes can have custom comparison and cast behavior.

An Overview

Here are all the object handlers with their signature and a small description.

zval *read_property(zend_object *object, zend_string *member, int type, void **cache_slot, zval *rv)
zval *write_property(zend_object *object, zend_string *member, zval *value, void **cache_slot)
int has_property(zend_object *zobj, zend_string *name, int has_set_exists, void **cache_slot)
void unset_property(zend_object *zobj, zend_string *name, void **cache_slot)
zval *get_property_ptr_ptr(zend_object *zobj, zend_string *name, int type, void **cache_slot)

These handlers correspond to the __get, __set, __isset and __unset methods. get_property_ptr_ptr is the internal equivalent of __get returning by reference. cache_slot is used to store the property offset and zend_property_info. read_property may directly return a zval owned by the object, in which case its reference count should not be modified by read_property, and the caller should not release it. Alternatively, it may return rv for temporary zvals (e.g. result of call to __get), in which case the refcount should be incremented, and the caller is responsible for releasing the value.

zval *read_dimension(zend_object *object, zval *offset, int type, zval *rv)
void write_dimension(zend_object *object, zval *offset, zval *value)
int has_dimension(zend_object *object, zval *offset, int check_empty)
void unset_dimension(zend_object *object, zval *offset)

This set of handlers is the internal representation of the ArrayAccess interface. zval *rv in read_dimension is used for temporary values returned from offsetGet and offsetExists.

HashTable *get_properties(zend_object *zobj)
HashTable *get_debug_info(zend_object *object, int *is_temp)

Used to get the object properties as a hashtable. The former is more general purpose, for example it is also used for the get_object_vars function. The latter on the other hand is used exclusively to display properties in debugging functions like var_dump. So even if your object does not provide any formal properties you can still have a meaningful debug output.

zend_function *get_method(zend_object **obj_ptr, zend_string *method_name, const zval *key)

The get_method handler fetches the zend_function used to call a certain method. Optionally key can be passed as an optimization to avoid lowercasing method_name in case it is already present.

zend_function *get_constructor(zend_object *zobj)

Like get_method, but getting the constructor function. The most common reason to override this handler is to disallow manual construction by throwing an error in the handler.

int count_elements(zend_object *object, zend_long *count)

This is just the internal way of implementing the Countable::count method. The function returns a zend_result and assigns the value to the zend_long *count pointer.

int compare(zval *o1, zval *o2)

The compare handler is a required handler that computes equality of the given object and another value. Note that the other value isn’t necessarily an object of the same class, or even an object at all. The handler should return negative numbers if the lhs is smaller, 0 if they are equal, or a positive number is the lhs is larger. If the values are uncomparable ZEND_UNCOMPARABLE should be returned.

int cast_object(zend_object *readobj, zval *writeobj, int type)

Internal classes have the ability to implement a custom compare behavior and override casting behavior for all types. Userland classes on the other hand only have the ability to override object to string casting through __toString.

int get_closure(zend_object *obj, zend_class_entry **ce_ptr, zend_function **fptr_ptr, zend_object **obj_ptr, bool check_only)

This handler is invoked when the object is used as a function, i.e. it is the internal version of __invoke. The name derives from the fact that its main use is for the implementation of closures (the Closure class).

zend_string *get_class_name(const zend_object *zobj)

This handler is used to get the class name from an object for debugging contexts. There should be little reason to overwrite it.

zend_object *clone_obj(zend_object *old_object)

The clone_obj handler is called when executing clone $old_object. By default PHP performs a shallow clone on objects, which means properties containing objects are not be cloned but both the old and new object will point to the same object. The clone_obj allows for this behavior to be customized. It’s also used to inhibit clone altogether.

HashTable *get_gc(zend_object *zobj, zval **table, int *n)

The get_gc handler should return all variables that are held by the object, so cyclic dependencies can be properly collected. If the object doesn’t maintain a property hashmap (because it doesn’t store any dynamic properties) it can use table to store a pointer directly into the list of zvals, along with a count of properties.

void dtor_obj(zend_object *object)
void free_obj(zend_object *object)

dtor_obj is called before free_obj. The object must remain in a valid state after dtor_obj finishes running. Unlike free_obj, it is run prior to deactivation of the executor during shutdown, which allows user code to run. This handler is not guaranteed to be called (e.g. on fatal error), and as such should not be used to release resources or deallocate memory. Furthermore, releasing resources in this handler can break detection of memory leaks, as cycles may be broken early. dtor_obj should be used only to call user destruction hooks, such as __destruct.

free_obj should release any resources the object holds, without freeing the object structure itself. The object does not need to be in a valid state after free_obj finishes running. free_obj will always be invoked, even if the object leaks or a fatal error occurs. However, during shutdown it may be called once the executor is no longer active, in which case execution of user code may be skipped.

int do_operation(zend_uchar opcode, zval *result, zval *op1, zval *op2)

do_operation is an optional handler that will be invoked for various arithmetic and binary operations on instances of the given class. This allows for operator overloading semantics to be implemented for custom classes. Examples for overloadable operators are +, -, *, /, ++, --, !.

zend_array *get_properties_for(zend_object *object, zend_prop_purpose purpose)

The get_properties_for can be used to customize the list of object properties returned for various purposes. The purposes are defined in zend_prop_purpose, which currently entails print_r, var_dump, the (array) cast, serialize, var_export and json_encode.