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PHP : Function Reference : Object property and method call overloading

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.

Warning:

This extension is not a part of PHP 5. PHP 5 supports __get(), __set() and __call() natively. See the Overloading in PHP 5 page for more information.

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. Starting with PHP 4.3.0 this extension is enabled by default. You can disable overload support with --disable--overload.

The windows version of PHP has built in support for this extension. You do not need to load any additional extension in order to use these functions.

Note:

Builtin support for overload is available with PHP 4.3.0.

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 1627. Overloading a PHP class

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<?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;
echo "\$o->a: $o->a\n"; // print: $o->a: 111
echo "\$o->b: $o->b\n"; // print: $o->b: 9
echo "\$o->c: $o->c\n"; // print: $o->c: 42
echo "\$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);

?>


Table of Contents

overload — Enable property and method call overloading for a class

Code Examples / Notes » ref.overload

upphpdoc
While this is a nice Feature it has nothing to do with Overloading as it is known in other OO-Languages.
What this feature does is allowing the dynamic addition of instance variables as e.g in Python.
Overloading means defining several methods with the same name in a single class. Which method will be called depends on the number and type of arguments specified. With dynamic and weak typed languages (like PHP) this can  of course not work.

muell-spam-trash-abfall
This is the syntax of __get(), __set() and __call():
__get ( [string property_name] , [mixed return_value] )
__set ( [string property_name] , [mixed value_to_assign] )
__call ( [string method_name] , [array arguments] , [mixed return_value] )
__call() seems to work with PHP 4.3.0
See http://www.phppatterns.com/index.php/article/articleview/28/1/2/ for using this extension in detail.

fabiostt x_at_x libero x_dot_x it
This extension has not much to do with overloading as we know it in Java or C++
We can sort of mimic overloading using call_user_func_array()
<?php
class OverloadTest{
   var $message ;
   function OverloadTest(){
       $numArgs = func_num_args() ; //number of args
       $args = func_get_args() ;  //array containing args
       call_user_func_array( array( &$this, 'OverloadTest'.$numArgs),  $args) ;
   }
   function overloadTest0(){
      $this->message = 'There are no args' ;
   }
   function overloadTest1($arg){
      $this->message = 'There\'s just one arg, its value is '.$arg ;
   }

function overloadTest2($arg1, $arg2){
      $this->message = 'There are 2 args, their values are '.join( func_get_args(), ', ') ;
   }

function getMessage(){

   return($this->message) ;

}
}//end class
$x = new OverloadTest('fooA', 'fooB') ;
echo( $x->getMessage() ) ;
?>

admin hat solidox dawt org
there are a couple of things you should be aware of when using overloading.
<?
class cTest
{
function __get($key, &$value)
{
echo "get: $key<br />";
return true;
}
function __set($key, $value)
{
echo "set: $key value: $value<br />";
return true;
}
function __call($method, $params, &$return)
{
echo "call: $method params: " . var_export($params, 1) . "<br />";
return true;
}
}
overload('cTest');
$cake = new cTest;
?>
firstly it should be noted that nested classes don't work.
secondly if you try to set an array it somehow becomes a get
and thirdly, if you call a nested class it picks the last nest as the method name, as opposed to a nested get which picks the first in the list.
<?
$x = $cake->hello->moto; //outputs "get: hello" moto is nowhere to be seen
$cake->hello['moto'] = 4; //outputs "get: hello"
$cake->moo->cow("hello"); //outputs "call: cow params: array ( 0 => 'hello', )"
?>
bit strange, these occur on php4.3.2. havn't tried other versions

jw
The following backwards compatible code demonstrates the differences between the PHP version 4 and 5 implementation of overloading:
<?
class Foo {
// The properties array
var $array = array('a' => 1, 'b' => 2, 'c' => 4);
// Getter
function __get($n, $val = "") {
if (phpversion() >= 5) {
return $this->array[$n];
} else {
$val = $this->array[$n];
return true;
}
}

// Setter
function __set($n, $val) {
$this->array[$n] = $val;
if (phpversion() < 5) return true;
}

// Caller, applied when $function isn't defined
function __call($function, $arguments) {
// Constructor called in PHP version < 5
if ($function != __CLASS__) {
$this->$arguments[0] = $arguments[1];
}
if (phpversion() < 5) return true;
}
}
// Call the overload() function when appropriate
if (function_exists("overload") && phpversion() < 5) {
overload("Foo");
}
// Create the object instance
$foo = new Foo;
// Adjust the value of $foo->array['c'] through
// method overloading
$foo->set_array('c', 3);
// Adjust the value of $foo->array['c'] through
// property overloading
$foo->c = 3;
// Print the new correct value of $foo->array['c']
echo 'The value of $foo->array["c"] is: ', $foo->c;
?>

justin b
Some useful things to know about overloading:
__call($m,$p,&$r) returns $r back to you, not whatever you put after the keyword return.  What you return determines whether or not the parser consideres the function defined.
__get($var,&$val) returns $val back to you, so fill up $val with what you want then return true or false, same as above.
when extending classes, you must overload the most extended level class for it to work:
class TestClass
{
   var $x = "x";
   var $y = "y";
   var $z = "z";
   function __call($method,$params,&$return)
   {
       $return = "Hello, you called $method with ".var_export($params,true)."
\n";
       return true;
   }
   function __get($var,&$val)
   {
       if($var == "l") { $val = $this->x; return true; }
       return false;
   }
}
overload('TestClass');
$test = new TestClass;
print $test->hello();
print $test->goodbye();
print $test->x;
print $test->l;
print $test->n;
class Test2 extends TestClass
{
}
$test2 = new Test2;
print $test2->hello();
/* output:
Hello, you called hello with array()
Hello, you called goodbye with array()
xx
Fatal Error: Call to undefined function hello() in ...
*/

kris - heehaw
Simple way to restrict class property access (read and/or write) and range checking on setting, custom get also.
<?php
final class test {
protected $x;
protected $y;
protected $z;
private $publicRead = Array(
'x'=>"",
'y'=>"",
'z'=>"getZ"
);
private $publicWrite = Array(
'x'=>"setX",
'y'=>"setY"
);
final public function test(){
$this->x = 0;
$this->y = 0;
$this->z = 100;
return $this;
}


final public function setX($val){
//allow only 1 - 10
if ($val > 0 && $val < 11){
$this->x = $val;
} else {
echo "Cannot set X to $val, valid range is 1-10\n<br />";
}
}

final public function setY($val){
//allow only 11 - 20
if ($val > 10 && $val < 21){
$this->y = $val;
} else {
echo "Cannot set Y to $val, valid range is 11-20\n<br />";
}
}

final public function getZ(){
return ($this->z*2)." (x2) ";
}

final private function __get($nm)
{
if (array_key_exists($nm, $this->publicRead)){
$method = $this->publicRead[$nm];
if ($method != ""){//if we have a custom get method use it
return $this->$method();
} else { //else return the value directly
return $this->$nm;
}
} else {
echo "Cannot get protected property ".get_class($this)."::$nm\n<br />";
return null;
}
}

final private function __set($nm, $val)
{
if (array_key_exists($nm, $this->publicWrite)){
$method = $this->publicWrite[$nm];
$this->$method($val);
} else {
echo "Cannot set protected property ".get_class($this)."::$nm\n<br />";
}
}
}
$t = new test;
$t->x = 1;
$t->y = 113;
$t->z = 1001;
echo "<br /><br />";
echo "X:".$t->x."<br />";
echo "Y:".$t->y."<br />";
echo "Z:".$t->z."<br />";
?>

metal
Overload and Inheritance.
After wasting a few hours trying to get it to work, it seems appropriate to put a warning here.
Short Version:
DON'T ever subclass an overloaded class. EVER.
Corollary:
If an overloaded class simply must be subclassed, rewrite the parent class to get rid of the overloading. It can be as simple as commenting out the overload() statement and calling the get/set/call methods explicitely.
This was the road I ended up taking.
Long Version:
While it is, in theory, possible to end up with a working subclass, it requires much mucking and OO-principles compromise.
There is a great post that details the problem at great length. For those with the stomach, the URL is:
http://www.zend.com/lists/engine2/200201/msg00140.html
If you're still thinking about mixing inheritance and overloading, at least read the "Best Practices for the overload functions" in the URL above. If that doesn't change your mind, at least you'll be able to avoid most of the pitfalls.

shores
One way to overcome the foreach overloading malfunction:
//non functioning:
foreach ($object->arrayProperty as $key => $value) { ... }
//functioning:
foreach (array_merge($object->arrayProperty) as $key => $value) { ... }
Bye!

josh
One thing about __get is that if you return an array it doesn't work directly within a foreach...
<?php
class Foo {
 function __get($prop,&$ret) {
   $ret = array(1,2,3);
   return true;
 }
}
overload ('Foo');
//works
$foo = new Foo;
$bar = $foo->bar;
foreach($bar as $n) {
 echo "$n \n";
}
//doesn't work (bad argument to foreach)
foreach($foo->bar as $n) {
 echo "$n \n";
}
?>
for loops also work fine..

daniel
Note that with this class:
<?php
class SillyClass
{
private $config = array();

       public function __construct()
{
$this->config['fruit'] = 'banana';
               $this->config['animal'] = 'monkey';
$this->config['shoppingList'] =
              array('drink' => 'milk', 'food' => 'cheeseburger');
}

      //Allow mySillyClass->someProperty style getting of
//anything that might happen to be in the $config array
//(returns NULL if not in the $config array).
public function __get($property)
{
if(isset($this->config->$property))
{
return $this->config->$property;
}
}
}
?>
The following code can not be used:
<?php
$mySillyClass = new SillyClass();
$drinkToBuy = $mySillyClass->shoppingList->drink;
?>
It seems that although there is no error, $mySillyClass->someProperty->someProperty
does *not* work (__get() is only called once).
It's not really a bug, and I'm sure PHP is behaving properly but it had me stumped for a while!

sdavey
It wasn't quite clear, but I found out that __get() and __set() only overload attributes that _don't_ exist.
For example:
<?
class Foo
{
var $a = "normal attribute";
function __get($key, &$ret)
{
$ret = "overloaded return value";
return true;
}
}
overload("Foo");
$foo = new Foo();
print "get a: $foo->a \n"; // prints:   get a: normal attribute
print "get b: $foo->b \n"; // prints:   get b: overloaded return value
?>
The important thing to note here is that $foo->a did not pass through __get(), because the attibute has been defined.
So it's more like "underloading" than "overloading", as it only virtualises attributes that _do not_ exist.

steve
If you are a perfectionist when it comes to your class interfaces, and you are unable to use overload(), there is another viable solution:
Use func_num_args() to determine how many arguments were sent to the function in order to create virtual polymorphism. You can create different scenarios by making logical assumptions about the parameters sent. From the outside the interface works just like an overloaded function.
The following shows an example of overloading a class constructor:
class Name
{
     var $FirstName;
     var $LastName;
     function Name($first, $last)
     {
           $numargs = func_num_args();

           if($numargs >= 2)
           {
                 $this->FirstName = $first;
                 $this->LastName = $last;
           }
           else
           {
                 $names = explode($first);
                 $this->FirstName = $names[0];
                 $this->LastName = $names[1]
           }
     }

}

john martin
I've found a work around that allows overload to work with nested classes.  I was trying to design a set of classes that I didn't need to define the setter/getter methods for each of the properties.  
I stayed away from the __get() and __set() function since this bypasses object encapsulation.  Instead I use the __call() method to implement the accessor functions.  The __call() function emulates the get{var name} and stores the variable into an internal array with in the class.  The get{var name} checks the array for the var name and returns it if found.
Using the Zend Dev Studio (Great Product!) I was able to debug the code and found that when overloaded objects are nested that the nested object somehow looses the array var.  Just for giggles, I added a second variable and assigned the array var by reference.  Some how this worked.  
class Base {
  var $_prop = array();
  var $_fix;
 
  function Base() {
     // This somehow fixes the problem with nested overloading
     $this->_fix = & $this->_prop;  
  }
}

evert
I use the overloader to perform a method-level permission check for objects
<?
class MyClass {
 function method1() {
  // .... //
 }
 function method2() {
 // .... //
 }
}
class ObjectProtector {
   var $obj;
   function ObjectProtector(&$object) {
      $this->obj =& $object;
   }
   function __call($m,$a,&$r) {
      if (myPermissionChecker(...)) {
        $r = call_user_func_array(array($this->obj,$m),$a);
        return true;
      } else return false;
   }
}
 
overload('ObjectProtector');
// Create your object
$myObj = new MyClass;
// Prodect your object
$myProtectedObj = new ObjectProtector($myObj);
//call your methods trough $myProtectedObj
$myProtectedObj->method1();
$myProtectedObj->method2('arguments');
?>
I'm not sure this is bad practice, but the engine allows it and it seems right.

dreamscape
I didn't see this posted anywhere, so here it is:
In PHP 4, if you are calling your overloaded class A from inside class B, you MUST include and overload class A before including class B.
I struggled with this one for some time, before attempting to change the include order of the classes, which then worked great.

none
I am coding a server with a lot of method. To avoid doing a $this->check_auth() call (and others similar processing) in _each_ on my method, I was looking for a way to wrap them all through a dispatch.
Combining _call, with call_user_func_array is the way I did it finally.
So basically, if you want to call "testFunc" you just call $class->test () and
it will be wrapped and testFunc will be executed.
<?php
class MytestClass
{
   function __call($method, $param)
       {
           // do anything here
           return (call_user_func_array (array ("MytestClass", $method."Func"), $param));
       }
   
   function testFunc($param, $arg)
       {
           echo "It works ! Param: $param, ARG=$arg\n";
           return true;
       }
}
$test = new MytestClass;
$test->test ("Cool", "Test");
?>

almethot
Here is a cleaner way to fake overloading which is a modification on fabiostt[X_AT_X]libero[X_DOT_X]it
12-Aug-2003 01:56 posting. This example allows you to reuse the object and not have to re-create the object everytime the variables need to change.
Hope this helps,
<?
Class NCSession
{
//Class Variables
Var $sessionResult = null;
// Sims Overloading in PHP - Yes it is crap but it works until you move to PHP 5.
function ncStartSession()
{
$numArgs = func_num_args() ; //number of args
$args = func_get_args() ;  //array containing args
$x = call_user_func_array( array( &$this, 'ncStartSession'.$numArgs),  $args) ;
$sessionResult = $x;
return $sessionResult;
}
function ncStartSession0()
{
session_start();
$sessionResult = "SUCCESS|YES|SESSIONID|" . session_id();
session_destroy();
return $sessionResult;
}
function ncStartSession1($arg)
{
session_start($arg);
$sessionResult = "SUCCESS|YES|SESSIONID|" . session_id();
session_destroy();
return $sessionResult;
       }
}
//End of Class
$myTestSession = NEW NCSession();
$myResult = $myTestSession->ncStartSession();
echo "\n\$myResult = $myResult\n";
?>

koert
Do not implement __call() if you need pass-by-reference of return-by-reference elswhere in your class.
For more information view php bug #25831. Unfortunately this bug is marked wont-fix.

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