LXXXII. Object property and method call overloading

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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.

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This extension is not a part of PHP 5. PHP 5 supports __get(), __set() and __call() natively. See PHP 5 migration chapter for more information.

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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.

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ע: Builtin support for overload is available with PHP 4.3.0.

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Some simple examples on using the overload() function:
�� 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; 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); ?>

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overload -- Enable property and method call overloading for a class

add a note User Contributed Notes
Object property and method call overloading

koert at idislikespam dot bitfactory dot nl
29-Sep-2004 02:36


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.

almethot at yahoo dot com
22-May-2004 07:33


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";



?>

Metal
15-Mar-2004 07:11


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:





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.

josh at uncommonprojects dot com
28-Feb-2004 02:45


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..

upphpdoc at upcd dot de
25-Feb-2004 08:58


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.

jw at jwscripts dot com
14-Feb-2004 07:10


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;



?>

sdavey at datalink dot net dot au
23-Jan-2004 09:45


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.

John Martin
09-Dec-2003 10:47


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;  

   }

}

admin (hat) solidox (dawt) org
25-Aug-2003 03:51


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: $method params: " . var_export($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

Justin B
13-Aug-2003 10:16


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 08:56


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 '.join( func_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 03:53


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  for using this extension in detail.

steve at walkereffects dot com
25-Feb-2003 06:32


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]

            }

      }

    

}

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LXXXII. Object property and method call overloading

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