PHP: rfc:propertygetsetsyntax-implementation-details

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====== Internal Implementation Details for Property Accessors ======
  * Version: 1.2
  * Updated: 2013-01-17
  * Author: Clint Priest <phpdev at zerocue dot com>
  * Contributors: Nikita Popov
  * RFC Document: [[https://wiki.php.net/rfc/propertygetsetsyntax-v1.2|v1.2 Document]]
  * The code for this RFC are available here: https://github.com/cpriest/php-src/tree/accessors

==== Overview ====

The current implementation of property accessors can be thought of as properties which have their read/write/isset/unset access 
guarded by accessor functions, the primary changes that permit this functionality to work are all within standard zend object handling
function calls.

The rest of the code changes are involved in compilation of the property accessor syntax, allowing for automatic implementation, etc.

Finally a few functions were added to reflection to reflect on the new features.

==== Memory Structure Changes ====

Accessor information is stored as an array of zend_function pointers added to the zend_property_info structure.

<code c>
typedef struct _zend_property_info {
	/* ... */
	union _zend_function **accs;
} zend_property_info;
</code>

The memory space is only allocated for the array of pointers if a property has accessors.

The correct accessor is referenced by using an enum value from the following new enum:

<code c>
/* Offsets into zend_property_info->accs */
typedef enum {
	ZEND_ACCESSOR_GET,
	ZEND_ACCESSOR_SET,
	ZEND_ACCESSOR_ISSET,
	ZEND_ACCESSOR_UNSET,
} zend_acc_index;
#define ZEND_NUM_ACCESSORS 4
</code>


==== Compilation Changes ====

During compilation if a guarded property is parsed it will create the given property, allocate the function pointer array 
and begin parsing the accessor code within the context of a function.  

Note that these functions are not methods of the class entry and are only referenced through the zend_function pointers of the 
property_info structure, this also means that they may not be called directly by userland code, only through accessing the
property using ordinary property access syntax.

==== zend_object_handler.c Changes ====

Each of the functions that handled read/write/isset/unset functionality checks to see if the property has accessors for 
the property and if so checks that there is an accessor for the specific action (read/write, etc) being performed and
handles the situation accordingly.


Much of the pre/post magic call code that %%__get/__set/__isset/__unset%% used was refactored and centralized into their respective zend_std_call_*() functions.
The new accessors also utilize these functions so that all pre/post condition handling is the same for accessors as they are for the magics.


A new function flag was added ZEND_ACC_CALL_GUARD which flags a function as "being called and guarded," this was necessary to allow for parent
accessors being able to be properly called. In the case of recursion with accessors a warning will be emitted if recursion is detected and that 
recursion is not called from the context of the validly scoped accessor.


For example a get accessor is allowed to get it's own value and does not produce a warning, but instead the ordinary property access routines occur while attempts to read that property from a context other than the get accessor will emit a warning and the value will be returned as NULL.


 * Error producing lines have been modified to produce a useful error report.  For example: Cannot override final property getter TimePeriod::$Hours

==== Static Accessors ====
Static accessors were abandoned due to the unique way in which static properties are presently handled, it would require significant engine changes to facilitate at this time and is
left for another RFC to refactor the static property handling to bring it more in line with existing zend_object_handlers.c code.

==== Tests ====
Roughly 80 additional tests were added to test the new accessors functionality, they are stored in ~/Zend/tests/accessors
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