Глава 18. Classes and Objects (PHP 4)

Содержание
class
extends
Constructors
Scope Resolution Operator (::)
parent
Serializing objects - objects in sessions
The magic functions __sleep and __wakeup
References inside the constructor
Comparing objects

class

A class is a collection of variables and functions working with these variables. A class is defined using the following syntax:

<?php
class Cart {
   var $items;  // Items in our shopping cart

   // Add $num articles of $artnr to the cart

   function add_item($artnr, $num) {
       $this->items[$artnr] += $num;
   }

   // Take $num articles of $artnr out of the cart

   function remove_item($artnr, $num) {
       if ($this->items[$artnr] > $num) {
           $this->items[$artnr] -= $num;
           return true;
       } elseif ($this->items[$artnr] == $num) {
           unset($this->items[$artnr]);
           return true;
       } else {
           return false;
       }
   }
}
?>

This defines a class named Cart that consists of an associative array of articles in the cart and two functions to add and remove items from this cart.

Внимание

You can NOT break up a class definition into multiple files. You also can NOT break a class definition into multiple PHP blocks, unless the break is within a method declaration. The following will not work:

<?php
class test {
?>
<?php
   function test() {
       print 'OK';
   }
}
?>

However, the following is allowed:

<?php
class test {
   function test() {
       ?>
        <?php
       print 'OK';
   }
}
?>

The following cautionary notes are valid for PHP 4.

Предостережение

The name stdClass is used internally by Zend and is reserved. You cannot have a class named stdClass in PHP.

Предостережение

The function names __sleep and __wakeup are magical in PHP classes. You cannot have functions with these names in any of your classes unless you want the magic functionality associated with them. See below for more information.

Предостережение

PHP reserves all function names starting with __ as magical. It is recommended that you do not use function names with __ in PHP unless you want some documented magic functionality.

In PHP 4, only constant initializers for var variables are allowed. To initialize variables with non-constant values, you need an initialization function which is called automatically when an object is being constructed from the class. Such a function is called a constructor (see below).

<?php
class Cart {
   /* None of these will work in PHP 4. */
   var $todays_date = date("Y-m-d");
   var $name = $firstname;
   var $owner = 'Fred ' . 'Jones';
   /* Arrays containing constant values will, though. */
   var $items = array("VCR", "TV");
}

/* This is how it should be done. */
class Cart {
   var $todays_date;
   var $name;
   var $owner;
   var $items = array("VCR", "TV");

   function Cart() {
       $this->todays_date = date("Y-m-d");
       $this->name = $GLOBALS['firstname'];
       /* etc. . . */
   }
}
?>

Classes are types, that is, they are blueprints for actual variables. You have to create a variable of the desired type with the new operator.

<?php
$cart = new Cart;
$cart->add_item("10", 1);

$another_cart = new Cart;
$another_cart->add_item("0815", 3);
?>

This creates the objects $cart and $another_cart, both of the class Cart. The function add_item() of the $cart object is being called to add 1 item of article number 10 to the $cart. 3 items of article number 0815 are being added to $another_cart.

Both, $cart and $another_cart, have functions add_item(), remove_item() and a variable items. These are distinct functions and variables. You can think of the objects as something similar to directories in a filesystem. In a filesystem you can have two different files README.TXT, as long as they are in different directories. Just like with directories where you'll have to type the full pathname in order to reach each file from the toplevel directory, you have to specify the complete name of the function you want to call: in PHP terms, the toplevel directory would be the global namespace, and the pathname separator would be ->. Thus, the names $cart->items and $another_cart->items name two different variables. Note that the variable is named $cart->items, not $cart->$items, that is, a variable name in PHP has only a single dollar sign.

<?php
// correct, single $
$cart->items = array("10" => 1);

// invalid, because $cart->$items becomes $cart->""
$cart->$items = array("10" => 1);

// correct, but may or may not be what was intended:
// $cart->$myvar becomes $cart->items
$myvar = 'items';
$cart->$myvar = array("10" => 1); 
?>

Within a class definition, you do not know under which name the object will be accessible in your program: at the time the Cart class was written, it was unknown that the object will be named $cart or $another_cart later. Thus, you cannot write $cart->items within the Cart class itself. Instead, in order to be able to access it's own functions and variables from within a class, one can use the pseudo-variable $this which can be read as 'my own' or 'current object'. Thus, '$this->items[$artnr] += $num' can be read as 'add $num to the $artnr counter of my own items array' or 'add $num to the $artnr counter of the items array within the current object'.

Замечание: The $this pseudo-variable is not usually defined if the method in which it is hosted is called statically. This is not, however, a strict rule: $this is defined if a method is called statically from within another object. In this case, the value of $this is that of the calling object. This is illustrated in the following example:

<?php
class A
{
   function foo()
   {
       if (isset($this)) {
           echo '$this is defined (';
           echo get_class($this);
           echo ")\n";
       } else {
           echo "\$this is not defined.\n";
       }
   }
}

class B
{
   function bar()
   {
       A::foo();
   }
}

$a = new A();
$a->foo();
A::foo();
$b = new B();
$b->bar();
B::bar();
?>

Результат выполнения данного примера:

$this is defined (a)
$this is not defined.
$this is defined (b)
$this is not defined.

Замечание: There are some nice functions to handle classes and objects. You might want to take a look at the Class/Object Functions.



Classes and Objects (PHP 4)
chris at simplekiosks dot com
13-Apr-2006 09:31
I took the above examples and extented them slightly to also allow you to run any function in the subclass without having to first declare it in the main class.

Enjoy

<?php

class mainClass
{
   /*
   * Class loading function.
   *
   *
   *
   *
   */

       var $module;

       function LoadClass($loadModule)
       {
             $this->module = new $loadModule; // this is much better
       }

       function RunFunction($FunctionName)
       {
           $this->module->$FunctionName();       
       }

       function ListFunctions()
       {

       }

     // function out()
     //{
     //    $this->module->out();
     // }
}

class subclass
{
   function out()
   {
       echo "Worked";
   }

   function NewFunction()
   {
       echo "<br>Good Lord<br>";
   }

   function ThirdFunction()
   {
       echo "<br>eh....<br>";

   }
}

echo "Start of class manulapations<br>";
//$loadModule = new subclass;
$mainclass=new mainClass;
$mainclass->LoadClass("subclass");
//$mainclass->out();
$mainclass->RunFunction('NewFunction');
//$mainclass->ThirdFunction();
echo "End of class manulapation<br>";
?>
Leonel Quinteros
09-Feb-2006 06:57
PHP Allow to extend a class in a dinamic way into a object and only affects that object not the others of the same class.

I was developing a persistence class and i found this:

<?php
class MyClass {
   var $Prop1;
  
   // Into the constructor i create a propertie that was not declared before.
   function MyClass() {
       $this->Prop2 = "This was not declared but now exists into the object";
   }

   function setProp($PropName, $PropValue) {
       $this->$PropName = $PropValue;
   }
}

$MyObj = new MyClass();
$MyObj->setProp("Prop1", "This was declared and now has value");
$MyObj->setProp("Prop3", "This was declared by setProp() method.");
$MyObj->Prop4 = "This was declared out of the class definition";

echo "Prop1: ".$MyObj->Prop1." <br />\r\n";
echo "Prop2: ".$MyObj->Prop2." <br />\r\n";
echo "Prop3: ".$MyObj->Prop3." <br />\r\n";
echo "Prop4: ".$MyObj->Prop4." <br />\r\n";

?>

This could be very useful, but very dangerous too, take care.
Wolverine
01-Feb-2006 09:30
In case you would like to interrupt object construction on some condition and return false for further checking:

<?php
class Foo
{
     // Constructor
     function Foo()
     {
           /*  Some inits here */

           $someval=false;

           if ($someval===false)
           {
               return false;
           }
     }
}

$obj=new Foo();    // This won't work and will return partially initialised object instead of false

class Bar
{
     // Constructor
     function Bar()
     {
           /*  Some inits here */

           $someval=false;

           if ($someval===false)
           {
               $this=false;
               return;
           }
     }
}

$obj2=new Bar();    // This will work as expected and return false
?>

Hope this helps some people.
Karim Ahmed
20-Oct-2005 12:46
This class method allows you to take a nice associative array of parameters into your class when the number of parameters gets unmanagable and/or has lots of default-value parameters.

It is so useful I suggest putting on a general base class (I call mine Object) so all your descendents can use it.

-----------------------------------------------------

Code:

-----------------------------------------------------

   function setClassVars( &$parameter_array )
   {
       $class            = get_class($this);
       $class_vars = get_class_vars($class);
       /*
       * check that each of the passed parameters are valid before setting the
       * appropriate class variable.
       */
       foreach ( $parameter_array as $var => $value ){
           if ( array_key_exists( $var, $class_vars ) ){       
               $this->$var = $value;
           }
           else{
               $this->raiseError(
                   'setClassVars: class variable "' .
                   $var .
                   '" does not exist on class "' .
                   $class . '"'
               );
           }
       }
   }
-----------------------------------------------------

for example:

A complicated, messy, class method Before:

-----------------------------------------------------
 render(
  &$business_object,
  $on_change=false,
  $on_blur=false,
  $options=false
  $name
 ){
   $this->business_object = $business_object;
   $this->name = $name;
   $this->on_blur = $on_blur;
   $this->options = $options;
   <code>
}
-----------------------------------------------------

A nice clean method After:

-----------------------------------------------------
 render(
  &$parameter_array
 ){
   $this->setClassVars($parameter_array);
   <code>
}
-----------------------------------------------------

Example call:

-----------------------------------------------------
$parameter_array =
 array(

  'business_object' => $business_object,
  'name' => $field_name,
  'on_change' => 'form.submit()',
  'on_blur' => 'javascript:validate()',

  $options =>
   array(
     '1' => 'None Selected',
     '2' => 'Blue',
     '3' => 'Red'

   )
 );

$my_object->render( &$parameters );
-----------------------------------------------------

Now isn't that easier to read AND maintain. Now you can change your API without the hassle of amending every call to the method! You no longer have to worry about where the default params are or even the order of your params.

I hope someone else who has been swearing at their code finds this useful ;-)
GamblerZG
14-Oct-2005 07:27
To pascal dot poncet at netconsult dot com:

That's why MySQL has aliases. You can simply do this:
<?php
mysql_query("SELECT found_rows() AS found_rows");
?>
pascal dot poncet at netconsult dot com
13-Oct-2005 07:22
Subject: using "sql_calc_found_rows" in a MySQL query while exploiting result in a PHP db class object.

Hello,

There is a nice function in MySQL that allows to know how many records would have been returned if no "where" clause were set : SQL_CALC_FOUND_ROWS.

If you have create a db object to collect the returned lines, you will be a little perplex when trying to call the result of this function.

Why ?
Simply because the returned field's name is "found_rows()" and obviously it's not possible to call something like :

<?php $result->found_rows() ?>

...as it will try to acces a method, not a property !

Then, the only way to get the right result seems to be the use of a class function, like :

<?php
  $db->query("select found_rows()");
  $count=current(get_object_vars(current($db->result)));
?>

Of course, if somebody found an other way to solve it, like a special syntax (see the one used with curled arrays in a string), I'm really open to discuss.

Good luck,
Pascal
Felix M dot Palmen <fmp at palmen dot homeip dot net>
10-Oct-2005 01:18
My way to implement a singleton in PHP4. I think it's the most convenient one since it works transparently using the constructor. Thanks to S.Radovanovic for his idea with referencing the class' variables, posted on manual/en/language.variables.scope.php

<?php

/* Singleton. Every instatiation returns the "same" object.
 *
 * for this to work, ALWAYS create objects with $object =& new class().
 * The reference operator doesn't do any harm in general and is
 * necessary for singletons.
 *
 * You also need to declare all the class' variables with "var" for
 * a singleton subclass. But that should always be a rule of good
 * design :)
 *
 * call parent::singleton() first in your subclass constructor.
 *
 * Of course, the subclass constructor should check if the object is already
 * initialized before doing any initialization.
 */

class singleton
{

  function singleton()
  {
   // static associative array containing the real objects, key is classname
   static $instances=array();

   // get classname
   $class = get_class($this);

   if (!array_key_exists($class, $instances))
   {
     // does not yet exist, save in array
     $instances[$class] = $this;
   }

   // PHP doesn't allow us to assign a reference to $this, so we do this
   // little trick and fill our new object with references to the original
   // class' variables:
   foreach (get_class_vars($class) as $var => $value)
   {
     $this->$var =& $instances[$class]->$var;
   }
  }

}

?>
dave at davidhbrown dot us
03-Oct-2005 09:10
It appears that one must use eval if calling a static function  where the name of the class is in a variable:

     echo $class::staticfunc();

gets you a "parse error, unexpected T_PAAMAYIM_NEKUDOTAYIM" (in PHP 4.4.0)

while
   echo eval("return $class::staticfunc();");

behaves as desired.

Contrast this limitation with `->`which will accept a variable on both sides -- e.g., $myClass->$myFunc() -- and, of course, new $myClass is perfectly happy. The expression myClass::$myFunc() also works.
ia [AT] zoznam [DOT] sk
28-Sep-2005 02:45
to Menno Vanderlist:
And why bother to use eval?

<?php
class mainClass
{ //mainClass
       var $module;

       function mainClass($loadModule)
       { // load modules
               //eval("\$this->module = new $loadModule;");

               $this->module = new $loadModule; // this is much better
       }

       function out()
       { //print out of loaded module
               $this->module->out();
       }
}
?>

Functionality is the same, without the overhead when using eval().
Menno Vanderlist
29-Jul-2005 09:31
Using the extends statement with classes works, but it did the reverse of what I wanted. I want a modules hiearchy that adds a module into the main module. So I tried the following, after not finding anyone else who has done it, and it worked :)

<?php

class subClassA
{ //subClassA
       function out()
       { //subClassA::outA()
               echo "testing subClassA\n";
       }
}

class subClassB
{ //subClassB
       function out()
       { //subClassB::outB()
               echo "testing subClassB\n";
       }
}

class mainClass
{ //mainClass
       var $module;

       function mainClass($loadModule)
       { // load modules
               eval("\$this->module = new $loadModule;");
       }

       function out()
       { //print out of loaded module
               $this->module->out();
       }
}

$mainA=new mainClass('subClassA');
$mainA->out();
$mainB=new mainClass('subClassB');
$mainB->out();
?>

outputs:
testing subClassA
testing subClassB
Niels Jaeckel
25-Apr-2005 01:37
My problem was, to write a class-method, that destroyes the class itself. After many hours I found the (assured) only possibility to implement this:

class A {

   function A() {

   }

   function DESTROY() {

     // this would not work:
     // unset($this);

     // but this:
     settype(&$this, 'null');

   }

}

This test-code worked on PHP 4.3.1:

$objA = new A();
var_dump($objA);        // Object...

$objA -> DESTROY();
var_dump($objA);        // NULL !!!

hth,
Niels
alberto dot delatorre at gmail dot com
11-Feb-2005 03:11
If you have a class hierarchy as this:

<?php
   abstract class A{
       //construct ommited
       public function load(){
           $this->_load();
       }

       protected abstract function _load();
   }
  
   class B extends A{
       protected function _load(){
           echo "loaded";
       }
   }
  
   $b = new B();
   $b->load();
?>

you encountered that you will have a 'calling an abstract method' in the line with '$this->_load'. To avoid this, just make another reference to $this and then call the method you'd want, this way:

<?php
   abstract class A{
       //construct ommited
       public function load(){
           $aux_this=&$this;
           $aux_this->_load();
       }

       protected abstract function _load();
   }
  
   class B extends A{
       protected function _load(){
           echo "loaded";
       }
   }
  
   $b = new B();
   $b->load();
?>
arjini at gmail dot com
04-Feb-2005 01:56
Didn't see this anywhere obvious, so I'm posting it here. To access a memeber of an array with another variable you use $arr[$name]

To access a class method or property, you use $obj->{$name} You can also use the return value of a function.

<?php
   class Test {
       function methodName(){
           echo 'works!';
       }   
   }
  
   function getName(){
       return 'methodName';
   }   
  
   $t = new Test();
   $t->{getName()}();

//works!
?>
spam at modem-help dot com
23-Jan-2005 09:32
Although the php 4.2.2 parser and variable storage are case-sensitive, classes + class-function + function declaration *storage* are not.

To example this, consider the following:

[note: constructor is `sendfile()', not `SendFile()' nor `sendFile()']
<?php
   class SendFile {
   // variables declared here

     function SendFile() {
     // function defined here
     }

     function sendFile() {
     // function defined here
     }

     function sendfile() {
     // function defined here
     }

   } // end class SendFile
?>

This was eventually illuminated by:

<?php
   print_r( get_declared_classes());
?>

...in which a snippet of the result is:

Array
(
   [0] => stdClass
   [1] => __PHP_Incomplete_Class
   [2] => Directory
   [3] => DomNode
   [4] => DomDocument
   [5] => DomParser
...
   [24] => sendfile
)

Specifically, it appears that php has used initial-caps for all of it`s own (internal) classes, but that all user-classes are stored lower-cased, as are class + ordinary functions.

Written in the hope of saving someone else time & grief from this interesting `feature'.
rdc_uk
22-Jan-2005 08:44
Just found this interesting "gotcha";

If you implement a class with no member variables, calling the constructor does NOT produce an object. This can be a source of (great) consternation when producing classes which need no data storage.

Essentially if your class has no data members, all its methods are ONLY available statically, this can be a pain if defining object hierarchies with abstract base classes...

Example:

class A
{
  function A()
  {
     $i = 0; // not an empty constructor!
  }

  function fn()
  {
   return "A";
  }
}

$obj_a = new A();

$obj_a == null
$obj_a->fn(); will generate an error
A::fn(); works

Simply putting a "var $status=0;" in the class suddenly makes your object instantiatable.

This is certainly a "quirk" in an OO implementation, possibly a bug, definitely worth watching out for...
php dot net at mechintosh dot com
05-Dec-2004 03:52
While it is possible to use the names of existing PHP functions for class method names (not that you *should*, however sometimes there's really only one good name for a method even if it's taken..), you cannot use the names of language constructs like list(), echo, print etc, and appearantly also not of eval().

But you probably shouldn't be using PHP functionnames anyway :-)
email at richardlee dot info
05-Sep-2004 10:11
An example of how to pass an object back into its own class for direct use.

(thisClass.php)

<?php

class thisClass{

   var $var1;
  
   function thisClass($value)
       {$this->var1 = $value;}
      
   function set_var1($value)
       {$this->var1 = $value;}
   function get_var1()
       {return $this->var1;}
  
   function showVar()       
       {echo "<p>var1 = ".$this->var1."</p>";}
  
   function callShowVar($object)
       {$object->showVar();}
  
   function copyObject($object)
       {$this->var1 = $object->get_var1();}

}

?>

(test.php)
<?php

require_once('class.php');

$thisObject = new thisClass(3);
$thatObject = new thisClass(1);

$thatObject->callShowVar($thisObject); //outputs "var1 = 3"

$thisObject->showVar(); //outputs "var1 = 3"
$thatObject->showVar(); //outputs "var1 = 1"
$thatObject->copyObject($thisObject);
$thatObject->showVar(); //outputs "var1 = 3"

?>
babs at sntteam dot org
31-Aug-2004 07:22
We can't split the class declaration in multiple PHP section but we can exit php tag in a function . ex :

<?
class plop {
   function plop() {
       $this->whatever = "bar";
   }
   function foo() {
       ?>
        <pre>foo returns <?=$this->whatever?></pre>
       <?
   }
};
$a = new plop;
$a->foo();
?>
will print : foo returns bar

PHP Version 4.3.8-9
bishop
19-Jul-2004 06:04
Say you have a factory method that needs to put data into an object before the constructor is called. This might be necessary, for example, if the factory class establishes a connection to a database and the manufactured object uses that connection in the constructor.

Do something like this:
<?php

function &factory($class /* ... */) {
  // 1) get an object shell
  $obj = new stdClass();

  // 2) "type cast" it to the desired class
  $tmp = explode(':', serialize($obj));
  $tmp[1] = strlen($class);
  $tmp[2] = '"' . $class . '"';
  $obj = unserialize(implode(':', $tmp));

  // 3) copy construct the manufacturer into the manufacturee
  $obj->copyFrom($this);

  // 4) call the real constructor
  $args = func_get_args();
  array_shift($args); // skip the class
  call_user_func_array(array (&$obj, $class), $args);

  return $obj;
}

?>

NOTE: The Editor's note in the "simon dot li at hongkong dot com" entry is misleading; it only works because the class names "foo" and "bar" are the same length. In general, you must change the first and second entries in serialized array as done above.

Also NOTE: This typecasting business works if you have a function that takes an arbitrary number of arguments and you want to pass those arbitrary arguments into a constructed class.  You can't just use call_user_func_array() in that case because 'new' is an operator, not a function.
catalin dot ivan at utoronto dot ca
06-Jul-2004 03:50
Regarding defining class variables:

The 'var' statement can NOT take Heredoc definitions, i.e. the "<<<MARKER" stuff (these may be somehow 'dynamic' as per warning above).

You must assign them values within the class constructor if you must use Heredoc.
oran at anonimous dot biu dot ac dot il
16-Jun-2003 10:34
class baseclass {
   function static1() {return "bla";}
   function static2() {return call_user_func(array(__CLASS__,'static1'));}
}

[ Editor's Note: Using the above, rather than below, will allow the static function to call its own generation's version of the method. ]

Unfortunately, inheritance of static methods is a bit problematic in PHP, because in order to use a static method you have to know the exact class it's defined in. This means trouble if you want to use one static function (or a static variable) from within another static function. For example:

class baseclass {
   function static1() {return "bla";}
   function static2() {return baseclass::static1();}
}

Now suppose that you write a class newclass that extends baseclass and redefines static1() to return "foo" instead of "bla" - this change will not be reflected in static2() of newclass. Not good at all.

You could use $this->static1() instead of baseclass::static1() in the definition of static2(), but then static2() will not be a static method. Another idea is to use get_class_name() to get the class name inside static2(), but again you need the $this variable to make this function call.

I found no way to overcome this problem, except to use real functions (not methods) for the purpose of wrapping my static functions. The name of the exact class to use is passed as a parameter to the wrapping function. It looks like this:

function wrapped_static1($clname) {
  if (in_array('static1', get_class_methods($clname)))
   return $clname::static1();
  return baseclass::static1();
}
function wrapped_static2($clname) {
  if (in_array('static2', get_class_methods($clname)))
   return $clname::static2();
  return baseclass::static2();
}

class baseclass {
   function static1() {return "bla";}
   function static2() {return wrapped_static1('baseclass');}
}

Now you can go on using baseclass and writing extension classes for it, using the following rules:
1. Use inheritance with your static functions in the natural way, as you would in C++. The wrapping code given here supports just 1 level of inheritance, but it may be improved to work its way up the inheritance tree using PHP's class functions.
2. When calling a static function, always call it through its wrapper.

For example:

class newclass extends baseclass    // example for rule 1
{
  function static1() {return 'foo';}
}
print static2_wrapper('newclass');  // example for rule 2

This is a little cumbersome, but now when you redefine a static function, you can be sure that any functions that rely on it will be able to use the correct definition.
russ dot taylor at nifty dot com
18-Apr-2003 01:31
It is sometimes useful to register a class instance as a session variable.  This can allow classes and their contained values to persist across multiple pages and/or frames.  Frames which need to use the registered class must be loaded (or reloaded) after the class instance is registered and the class declaration must be included in each file that needs to access the registered class.

i.e.
<?
session_start();// must have a session, duh...

class foo{//normal class declaration

  var $bar;

  function foo(){//normal constructor
   $this->bar = "a value to share and persist";
  }
}

$vital = new foo;//instance "vital" of object type "foo"

session_register("vital");//register the instance "vital"

//other code as needed

?>

**NOTE: it would be helpful to include the class from an external source so the same declaration could be used everywhere its needed, duh

then simply include the class declaration in any other file and you will have access to the registered class instance.  in a separate frame on the same page you could use ...

<?
session_start();

class foo{//same class declaration

  var $bar;

  function foo(){//normal constructor
   $this->bar = "a value to share and persist";
  }
}

echo $vital->bar;

?>

**NOTE: if you use a frameset you must allow processing time of the session registration or the value will not be available!  You can use any number of methods to trigger the delay, but the session must NOT be started on the second page beforre the variable is registered on the first.  On option is to use an onload statement in the first frames body tag, assuming normal html output...

<html><head></head><body onLoad="parent.frame[1].location.reload();"><!--what ever else you need to output--></body></html>

"frame[1]" assumes a two frame layout with frame[0] containing the values to share and frame[1] requiring those values. thus this, when included in frame[0] will force a reload of frame[1] AFTER the class instance was registered.
mcoakley at netplay dot net
17-Jan-2003 08:47
In response to the comments above and using tomcats example directly... I love scripting languages and I love PHP the most out of them. While most programmers (and editors notes) try to state that PHP is not a true OO language it has what you need to develop good OO programs. Sure some of the really strong structured things aren't there but that is the fun you get with scripted languages. But after reading every comment on this page I think people (and I know I am going to get flamed for this one...) should start to fully understand the principles of OO programming: Encapsulation, Polymorphism and Abstraction.

For those new to those terms:
- Encapsulation is what you get when you can have data and the methods that act on those data in an "encapsulated" entity (object)
- Polymorphism is a property of objects that comes through inheritence that allows methods of the same name to perform different (but similar in purpose) actions
- Abstration provides a mechanism to design effective OO heirarchies by pulling common methods or actions into superclasses and using inheritence to provide functionality

If these principles are understood fully, PHP can be used as a great OO language.  Another common complaint is that PHP doesn't offer private/protected members/methods, I too would like to see these features. One BIG thing to keep in mind while desiging an OO program is that the objects should provide funtionality at the class level. Don't think of objects as individual entities but think of a heirarchy that provides "blackboxes" of code. In otherwords the class names should tell you what the object does and the methods only tell you how to invoke the functionality. You should never be concerned with how the object achieves its functionality.
b dot ruecker at portunity dot de
08-Jul-2001 09:22
If you need a destructor, perhaps it is an idear to simulate it this way with a global Destroy-Function:

<?
function DestroyObject ($name)
{
     $theobject = &$GLOBALS[$name];
     if (method_exists ($theobject,"Destroy"))
         $theobject->Destroy ();
     unset ($GLOBALS[$name]);
}

class xyz
{
   var $somevar;

   // ### This is the constructor
   function xyz ()
   {
   }

   // ### This is the destructor which will be called
   function Destroy ()
   {
       echo ("Now we destroy it !");
   }

   function SomeDo ()
   {
       echo ("doing something: ".$this->somevar);
   }
}

$example = new xyz;

// .... doing something here
$example->somevar = 3;
$example->SomeDo();

DestroyObject ("example");

// ### Test => should produce an error !
$example->SomeDo ();

?>
sgarner at expio dot co dot nz
18-Feb-2001 06:15
[Editor's note: Remember tha PHP is not a hard core OOP language, and even the ones that are do not always support the unusual vector/array references applied to results from methods.]

It seems there is no way to access the return value of a method (or any function) inline, without assigning it to a variable.

For example:

<?php
class Test
{
  function blah ()
  {
     return array(1,2,3);
  }

  function childTest ()
  {
     return new Test;
  }
}

$test = new Test;

// This does not work:
$foo = $test->blah()[0];

// Instead have to do:
$temp = $test->blah();
$foo = $temp[0];

// Similarly for objects, cannot do:
$foo = $test->childTest()->blah();

// Instead have to do:
$temp = $test->childTest();
$foo = $temp->blah();

?>
buzz77 at gmx dot net
14-Feb-2001 08:33
You can also store object variables as session variables, so that you don't have to create an object every time the page loads.

Let's see how:
here is my simple class file:

// simple.lib.php
class simple
{
  function dummy
  {
   print "TEST SUCCESSFUL!\n";
  }
}

Then, I create a simple .php which starts a new session and registers the object-variable of the "simple"-class.

// test1.php
require ("simple.lib.php");
session_start();
session_register("CLASSOBJ");
$CLASSOBJ=new simple();

That's all.
In the following .php-files you've only to add the following lines:
require("simple.lib.php");
session_start();

To test out if it works, simply call:
$CLASSOBJ->dummy();
and it will print the message.

I tried it out also with quite huge classes, and it always worked (I think the pointer to the instanciated class is stored and the class object itself won't be deleted if you eg. change to another .php-page)
brice at webprojkt dot com
21-Dec-2000 09:23
Defaulting a function parameter to a variable isn't directly supported, but here's how to get around that:

Suppose you have a class:

class query {
   var $sql;
   var $link;

   function go ($SQLstring = $this->sql)
   {
     return mysql_query($this->sql,$link);
   }
}

This doesn't work.  Here's the workaround:

(function spec):
   function go ($SQLstring)
   {
     if (isset($SQLstring)) { $this->sql = $SQLstring; }
     return mysql_query($this->sql,$this->link);
   }

This may not be the best example of this, but I thought I'd throw this out for you folks ... should allow support of presetting of an object value and then execution of the method on that, or something like query::go("SELECT ...");

Enjoy!

p.s. (in this case query::go wouldn't work because it is coded with $this->link, but if you wanted to just use the default connection, it'd work fine :)
iw at warped dot nu
08-Oct-2000 05:12
Here's a very important reminder to those of you used to Java/C++ object references/pointers. When you send a function arguments which include a class object, PHP will make copies of that object for use inside that function.

This differs from passing a Java reference to an object or passing a C++ pointer to an object. Within the scope of the above-mentioned function, calling class methods of the argument object will only affect the copy that PHP creates. Likewise, when the function itself is completed, the copy of the object you passed ceases to exist.

To emulate Java/C++ functionality of arguments that are objects, you just have to modify the given function's signature from this:

function foo(..., $object, ...)

to this:
function foo(..., &$object, ...)

The ampersand(&) thus signifies that the function should receive a reference to the object, instead of creating a copy of the object.
simon dot li at hongkong dot com
13-Sep-2000 04:15
-------------------------------------------------
[Editor's note: class casting per se is not part of the object/class implementation in PHP, but code like the one in this note can kludge if you need it for very simple cases, more complex ones are left to the imagination of the programmer:
<?php
class foo {
   function foo($name="foo") {
       $this->name=$name;
   }
}

class bar extends foo {
   function boom() {
       echo "BOOOM!";
   }
}

$f = new foo();
$temp = explode(":",serialize($f));
$temp[2] = "\"bar\"";
$b = unserialize(implode(":",$temp));

$b->boom();

?>
This forces $b to be an instance of "bar" using an object $f, an instance of "foo"]
-------------------------------------------------


About casting of object, say, i got:

class A extends B {
       function A() {
               $this->B();
       }
       ....
}

$b = new B();
$a = new A();

I wanna have a object of class A with "content" of $b:
$a = (A) $b; // not a valid code,(right?) as for illustration.

<Встроенные функцииextends>
 Last updated: Tue, 15 Nov 2005