Object property and method call overloading

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# LXXVI. Object property and method call overloading

# Introduction

The purpose of this extension is to allow overloading of object property access and method calls. Only one function is defined in this extension, overload() which takes the name of the class that should have this functionality enabled. The class named has to define appropriate methods if it wants to have this functionality: `__get()`, `__set()` and `__call()` respectively for getting/setting a property, or calling a method. This way overloading can be selective. Inside these handler functions the overloading is disabled so you can access object properties normally.

Warning
This extension is EXPERIMENTAL. The behaviour of this extension -- including the names of its functions and anything else documented about this extension -- may change without notice in a future release of PHP. Use this extension at your own risk.

# Requirements

No external libraries are needed to build this extension.

# Installation

In order to use these functions, you must compile PHP with the `--enable-overload` option.

# Runtime Configuration

This extension has no configuration directives defined in `php.ini`.

# Resource Types

This extension has no resource types defined.

# Predefined Constants

This extension has no constants defined.

# Examples

Some simple examples on using the overload() function:

Example 1. Overloading a PHP class
    <?php

    class OO
    {
        var $a = 111;
        var $elem = array('b' => 9, 'c' => 42);

        // Callback method for getting a property
        function __get($prop_name, &$prop_value)
        {
            if (isset($this->elem[$prop_name])) {
                $prop_value = $this->elem[$prop_name];
                return true;
            } else {
                return false;
            }
        }

        // Callback method for setting a property
        function __set($prop_name, $prop_value)
        {
            $this->elem[$prop_name] = $prop_value;
            return true;
        }
    }

    // Here we overload the OO object
    overload('OO');

    $o = new OO;
    print "\$o->a: $o->a\n"; // print: $o->a:
    print "\$o->b: $o->b\n"; // print: $o->b: 9
    print "\$o->c: $o->c\n"; // print: $o->c: 42
    print "\$o->d: $o->d\n"; // print: $o->d:

    // add a new item to the $elem array in OO
    $o->x = 56;

    // instantiate stdclass (it is built-in in PHP 4)
    // $val is not overloaded!
    $val = new stdclass;
    $val->prop = 555;

    // Set "a" to be an array with the $val object in it
    // But __set() will put this in the $elem array
    $o->a = array($val);
    var_dump($o->a[0]->prop);

    ?>

Warning
As this is an experimental extension, not all things work. There is no `__call()` support currently, you can only overload the get and set operations for properties. You cannot invoke the original overloading handlers of the class, and `__set()` only works to one level of property access.

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