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Last updated: Thu, 21 Aug 2003

LXXVII. 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. 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 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.

Table of Contents
overload -- Enable property and method call overloading for a class


add a note add a note User Contributed Notes
Object property and method call overloading
admin (hat) solidox (dawt) org
25-Aug-2003 10:51
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: $method params: " var_export($params1) . "<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"

$cake->moo->cow("hello"); //outputs "call: cow params: array ( 0 => 'hello', )"
?>
bit strange, these occur on php4.3.2. havn't tried other versions
Justin B
13-Aug-2003 05:16
Some useful things to know about overloading:
__call($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)."<br>\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 ...
*/
fabiostt[X_AT_X]libero[X_DOT_X]it
12-Aug-2003 03:56
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 '.joinfunc_get_args(), ', ') ;

    }
       
        function 
getMessage(){
       
            return(
$this->message) ;
       
        }

}
//end class

$x = new OverloadTest('fooA''fooB') ;

echo( 
$x->getMessage() ) ;

?>
muell-spam-trash-abfall at kcet dot de
14-Mar-2003 11:53
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.
steve at walkereffects dot com
25-Feb-2003 02:32
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]
            }
      }
   
}

<ob_startoverload>
 Last updated: Thu, 21 Aug 2003
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