PHP 8.0.24 Released!

Nesnelerin Kalıtımı

Kalıtım iyi kurgulanmış bir programlama prensibidir ve PHP bu prensibi kendi nesne modelinde kullanır. Bu prensip çoğu sınıf ve nesnenin bir diğeri ile ilişkisini düzenler.

Örneğin, bir sınıf (extend ile) genişletildiğinde alt sınıf üst sınıftaki genel ve korunmuş yöntemlerin tümünü miras alır. Bir sınıf bu yöntemleri aynı isimdeki yöntemlerle geçersizleştirmedikçe bunlar özgün işlevselliklerini korur.

Bu, işlevselliği tanımlamak ve soyutlamak için ve paylaşılan işlevselliğin tamamını yeni baştan gerçeklemeksizin benzer nesnelerde ek işlevsellikleri gerçeklemek için kullanışlıdır.

Bir ebeveyn sınıfın private yöntemlerine bir çocuk sınıftan erişilemez. Sonuç olarak, normal miras alma kurallarına aldırmadan çocuk sınıfların bu private yöntemleri yeniden gerçeklemesi gerekebilir. PHP 8.0.0 öncesinde, private yöntemlere bunun yanında final ve static sınırlamaları da uygulanırdı. PHP 8.0.0 ve sonrasında zorunlu olan tek private yöntem kısıtlaması, private final kuruculardır, çünkü bu, yerleşik statik yöntemleri kullanırken kurucuyu "devre dışı" bırakmanın yaygın bir yoludur.

Yöntemlerin, özelliklerin ve sabitlerin görünürlüğü gevşetilebilir, örn. protected bir yöntem public olarak imlenebilir; ancak sınırlandırılamaz, örneğin bir public özellik, private olarak imlenebilir.

Bilginize:

Otomatik yükleme kullanılmadıkça, sınıflar kullanılmadan önce tanımlanmalıdır. Eğer bir sınıf diğerini genişletiyorsa ebeveyn sınıf çocuk sınıfın yapısı kurulmadan önce bildirilmiş olmalıdır. Bu kural diğer sınıfları ve arayüzleri miras alan tüm sınıflara uygulanır.

Bilginize:

Okunup yazılabilir bir özellik salt-okunur özellik vb. ile geçersiz kılınamaz.

<?php

class {
    public 
int $prop;
}
class 
extends {
    
// Geçersiz: oku-yaz özellik salt-okunur yapılamaz
    
public readonly int $prop;
}
?>

Örnek 1 Kalıtım Örneği

<?php

class Foo
{
    public function 
printItem($string)
    {
        echo 
'Foo: ' $string PHP_EOL;
    }

    public function 
printPHP()
    {
        echo 
'PHP is great.' PHP_EOL;
    }
}

class 
Bar extends Foo
{
    public function 
printItem($string)
    {
        echo 
'Bar: ' $string PHP_EOL;
    }
}

$foo = new Foo();
$bar = new Bar();
$foo->printItem('baz'); // Çıktısı: 'Foo: baz'
$foo->printPHP();       // Çıktısı: 'PHP is great'
$bar->printItem('baz'); // Çıktısı: 'Bar: baz'
$bar->printPHP();       // Çıktısı: 'PHP is great'

?>

Dahili Sınıflar ve Dönüş Türü Uyumluluğu

PHP 8.1 öncesinde, dahili sınıfların vaya yöntemlerin çoğunda dönüş türü bildirimi yoktu ve bunları genişletirken dönüş türüne izin veriliyordu.

PHP 8.1.0 ve sonrasında, çoğu dahili yöntem dönüş türlerini "geçici olarak" bildirmeye başladı, bu durumda yöntemin dönüş türü, genişletilen ebeveyn ile uyumlu olmalıdır; aksi takdirde, bir kullanımdan kaldırma bildirimi çıktılanır. Açık bir dönüş türü bildiriminin olmayışı, ayrıca yapısal bir uyuşmazlık olarak kabul edilmekte ve dolayısıyla kullanımdan kaldırma bildirimiyle sonuçlanmaktadır.

PHP'nin sürümler arası uyumluluk endişeleri nedeniyle geçersiz kılma yöntemi için dönüş türü bildirilemezse, kullanımdan kaldırma bildirimini sessizleştirmek için #[ReturnTypeWillChange] özniteliği eklenebilir.

Örnek 2 - Dönüş türünü bildirmeyen geçersiz kılma yöntemi

<?php
class MyDateTime extends DateTime
{
    public function 
modify(string $modifier) { return false; }
}

// "Deprecated: Return type of MyDateTime::modify(string $modifier) should either be compatible with DateTime::modify(string $modifier): DateTime|false, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice" as of PHP 8.1.0
// Kullanımı önerilmiyor: MyDateTime::modify(string $modifier) için dönüş türü ya  DateTime::modify(string $modifier): DateTime|false ile uymlu olmalı ya da PHP 8.1.0 ve sonrasında uyarıyı susturmak için #[\ReturnTypeWillChange] özniteliği kullanılmış olmalıdır.
?>

Örnek 3 - Yanlış dönüş türü bildiren geçersiz kılma yöntemi

<?php
class MyDateTime extends DateTime
{
    public function 
modify(string $modifier): ?DateTime { return null; }
}

// "Deprecated: Return type of MyDateTime::modify(string $modifier): ?DateTime should either be compatible with DateTime::modify(string $modifier): DateTime|false, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice" as of PHP 8.1.0
// Kullanımı önerilmiyor: MyDateTime::modify(string $modifier): ?DateTime için dönüş türü ya DateTime::modify(string $modifier): DateTime|false ile uymlu olmalı ya da PHP 8.1.0 ve sonrasında uyarıyı susturmak için #[\ReturnTypeWillChange] özniteliği kullanılmış olmalıdır.
?>

Örnek 4 - Yanlış dönüş türü bildiren ama kullanımı önerilmiyor uyarısı vermeyen geçersiz kılma yöntemi

<?php
class MyDateTime extends DateTime
{
    
/**
     * @return DateTime|false
     */
    #[ReturnTypeWillChange]
    
public function modify(string $modifier) { return false; }
}

// Bir uyarı tetiklenmez
?>
add a note

User Contributed Notes 17 notes

up
205
jackdracona at msn dot com
12 years ago
Here is some clarification about PHP inheritance – there is a lot of bad information on the net.  PHP does support Multi-level inheritance.  (I tested it using version 5.2.9).  It does not support multiple inheritance.

This means that you cannot have one class extend 2 other classes (see the extends keyword).  However, you can have one class extend another, which extends another, and so on.

Example:

<?php
class A {
       
// more code here
}

class
B extends A {
       
// more code here
}

class
C extends B {
       
// more code here
}


$someObj = new A();  // no problems
$someOtherObj = new B(); // no problems
$lastObj = new C(); // still no problems

?>
up
91
Mohammad Istanbouly
5 years ago
I think the best way for beginners to understand inheritance is through a real example so here is a simple example I can gave to you

<?php

class Person
{
    public
$name;
    protected
$age;
    private
$phone;

    public function
talk(){
       
//Do stuff here
   
}

    protected function
walk(){
       
//Do stuff here
   
}

    private function
swim(){
       
//Do stuff here
   
}
}

class
Tom extends Person
{
   
/*Since Tom class extends Person class this means
        that class Tom is a child class and class person is
        the parent class and child class will inherit all public
        and protected members(properties and methods) from
        the parent class*/

     /*So class Tom will have these properties and methods*/

     //public $name;
     //protected $age;
     //public function talk(){}
     //protected function walk(){}

     //but it will not inherit the private members
     //this is all what Object inheritance means
}
up
24
strata_ranger at hotmail dot com
12 years ago
I was recently extending a PEAR class when I encountered a situation where I wanted to call a constructor two levels up the class hierarchy, ignoring the immediate parent.  In such a case, you need to explicitly reference the class name using the :: operator.

Fortunately, just like using the 'parent' keyword PHP correctly recognizes that you are calling the function from a protected context inside the object's class hierarchy.

E.g:

<?php
class foo
{
  public function
something()
  {
    echo
__CLASS__; // foo
   
var_dump($this);
  }
}

class
foo_bar extends foo
{
  public function
something()
  {
    echo
__CLASS__; // foo_bar
   
var_dump($this);
  }
}

class
foo_bar_baz extends foo_bar
{
  public function
something()
  {
    echo
__CLASS__; // foo_bar_baz
   
var_dump($this);
  }

  public function
call()
  {
    echo
self::something(); // self
   
echo parent::something(); // parent
   
echo foo::something(); // grandparent
 
}
}

error_reporting(-1);

$obj = new foo_bar_baz();
$obj->call();

// Output similar to:
// foo_bar_baz
// object(foo_bar_baz)[1]
// foo_bar
// object(foo_bar_baz)[1]
// foo
// object(foo_bar_baz)[1]

?>
up
14
akashwebdev at gmail dot com
7 years ago
The Idea that multiple inheritence is not supported is correct but with tratits this can be reviewed.

for e.g.

<?php
trait  custom
{
     public function
hello()
     {
          echo
"hello";
     }
}

trait
custom2
{
       public function
hello()
       {
            echo
"hello2";
       }
}

class
inheritsCustom
{
        use
custom, custom2
       
{
             
custom2::hello insteadof custom;
        }
}

$obj = new inheritsCustom();
$obj->hello();
?>
up
1
niemans at pbsolo dot nl
2 years ago
Inheritance works at create time, i.e. using the keyword 'new'. Static properties confused my understanding, so in order tho show the effect of visibility to inherintence I've created a simple demo script along with some set and get magic:

<?php
class A {
private
$a   = 'private';
protected
$b = 'protected';
public
$c    = 'public';
static
$d    = 'static';
public function
__construct()
{
   
$this->e = 'constructed';
}
public function
__set($property, $value)
{
    echo
' set ' . $property . '=' . $value;
   
$this->$property=$value;
}
public function
__get($property)
{
    echo
' get ' . $property;
   
$this->$property = 'dynamic'// invokes __set() !!
   
return $this->$property;
}
}

class
B extends A
{
public function
constructMe()
{
   
$this->e = 'constructed2';
}
}

class
C extends B
{
public function
__construct()
{
   
parent::constructMe();
}
}

echo
" \n";
$a = new A();
$b = new B();
echo
" \n";
echo
' B:c='.$b->c;
echo
" \n";
echo
' B:d=' .$b->d;
echo
" \n";

$c = new C();
echo
" \n";

print_r($a);
print_r($b);
print_r($c);

print_r(A::$d);
print_r(B::$d);
print_r(C::$d);

echo
'A class: ';
$R = new reflectionclass('A');
print_r($R->getdefaultproperties());
print_r($R->getstaticproperties());
echo
'B class: ';
$R = new reflectionclass('B');
print_r($R->getdefaultproperties());
print_r($R->getstaticproperties());

?>

This outputs:

set e=constructed
B:c=public
get d set d=dynamic B:d=dynamic
set e=constructed2
A Object
(
    [a:A:private] => private
    [b:protected] => protected
    [c] => public
    [e] => constructed
)
B Object
(
    [a:A:private] => private
    [b:protected] => protected
    [c] => public
    [d] => dynamic
)
C Object
(
    [a:A:private] => private
    [b:protected] => protected
    [c] => public
    [e] => constructed2
)
staticstaticstaticA class: Array
(
    [d] => static
    [a] => private
    [b] => protected
    [c] => public
)
Array
(
    [d] => static
)
B class: Array
(
    [d] => static
    [b] => protected
    [c] => public
)
Array
(
    [d] => static
)

This shows how private variables ($a) are inherited, how static variables ($d) are inherited (by the class, not by the object) and that changing or adding variables in the parent ($e, $d) are not inherited by the child.
up
10
jarrod at squarecrow dot com
12 years ago
You can force a class to be strictly an inheritable class by using the "abstract" keyword. When you define a class with abstract, any attempt to instantiate a separate instance of it will result in a fatal error. This is useful for situations like a base class where it would be inherited by multiple child classes yet you want to restrict the ability to instantiate it by itself.

Example........

<?php

abstract class Cheese
{
     
//can ONLY be inherited by another class
}

class
Cheddar extends Cheese
{
}

$dinner = new Cheese; //fatal error
$lunch = new Cheddar; //works!

?>
up
-3
Anonymous
3 years ago
PHP7 gives you a warning if you redeclare a function in a child class with different parameters. For example:

class foo {
     function print($text='') {
          print text;
     }
}

class bar extends foo {
      function print($text1='',$text2='') {
           print text1.text2
      }
}

will give a PHP Warning:  Declaration of bar::print($text1 = '', $text2 = '') should be compatible with foo::print($text= '').
up
-2
sibian0218 at gmail dot com
4 years ago
I've noticed one thing concerning inheritance...
When declaring an abstract class with a private method,
which is overridden by a sub-class, private takes precedence over public for child class...
(in the case you're redeclaring a method with a different signature in fact).

Hope this helps
up
-4
Sam Tigall
3 years ago
Overriding a method which is called from base class works like this:

<?php
class Foo
{
    public function
printItem($string)
    {
        echo
'Foo: ' . $string;
    }
   
    public function
printPHP($string)
    {
       
$this->printItem($string);
    }
}

class
Bar extends Foo
{
    public function
printItem($string)
    {
        echo
'Bar: ' . $string ;
    }
}

$foo = new Foo();
$bar = new Bar();
$foo->printPHP('baz'); //Foo: baz
$bar->printPHP('baz'); //Bar: baz
?>
up
-7
nemanja
5 years ago
Even when autoloading (SPL) is used, class inheritance does not seem to work. Simply the PHP engine is unable to find parent (inherited) class. PHP 5.6 and 7.0 behave exactly same on this, which beats the purpose of autoloading.

And IMHO it's easy to fix as the autoloader is able to find all first level classes w/o problems, it just needs to follow same path recursively on parents too.

<?php
//Using default SPL autoloader, with namespaces mapping 1:1 to directory structure, with file names being all lowercase.
//This works with first level classes only, for inheritance it does NOT work, it cannot find parent classes.
spl_autoload_register();

//This is ugly but working code if you want to be able to autoload parent classes too.
spl_autoload_register(function ($class){
    require_once
__DIR__ . '/' . strtolower(str_replace('\\', '/', $class) . '.php');
});
up
-8
gino dot d at amail dot com
5 years ago
A simple trait to create multi inheritance in php

<?php

trait tExtend {
    private
$objectExtend = [];

    final public function
extend() {
        foreach (
$objects = func_get_args() as &$object) {
            if (
is_object($object) && !$object instanceOf self) {
               
$this->objectExtend[] = $object;
               
                if (
is_callable([$object, 'syncExtend']))
                   
$object->syncExtend($this, $objects);
            }
        }
    }

    final public function
syncExtend(&$object = null, array $objects) {
        if (
is_object($object) && !$object instanceOf self && !in_array($object, $this->objectExtend))
           
$this->objectExtend[] = $object;

        foreach (
$objects as &$object)
            if (
is_object($object) && !$object instanceOf self && !in_array($object, $this->objectExtend))
               
$this->objectExtend[] = $object;

        return
$this;
    }

    final public function
__call($method, $args) {
        if (
method_exists($this, $method))
            return
$this->{$method}(... $args);
        else {
            foreach (
$this->objectExtend as $i => &$object) {
                if (
method_exists($object, $method))
                    return
$object->{$method}(... $args);
            }
        }

        throw new \
Exception('Call to undefined method ' . get_called_class() .  '::' . $method . '()');
    }

    final public function
__get($key) {
        if (
array_key_exists($key, $this))
            return
$this->{$key};

        foreach (
$this->objectExtend as &$object) {
            if (
array_key_exists($key, $object))
                return
$object->{$key};
        }

       
trigger_error('Undefined property: ' . get_called_class() . '::$' . $key, E_USER_NOTICE);
    }

    final public function
__isset($key) {
        if (
array_key_exists($key, $this))
            return
true;

        foreach (
$this->objectExtend as &$object) {
            if (
array_key_exists($key, $object))
                return
true;
        }

        return
false;
    }
}

/*************/

class F {
    public
$relationship = 'Sister';
}

class
M {
    public
$relationship = 'Brother';
}

class
A extends M {
    use
tExtend;
}
class
B extends F {
    use
tExtend;

    function
getName() {
        return
'B';
    }
}
class
C extends F {
    use
tExtend;

    function
getName() {
        return
'C';
    }
}
class
D extends M {
    use
tExtend;
}

class
{
    use
tExtend;

    function
getParent() {
        return
'Z';
    }

    function
__construct() {
       
$this->extend(... func_get_args());
    }
}

$a = new A;
$b = new B;
$c = new C;
$d = new D;
$z = new Z($a, $b, $c, $d);

$d->extend($a); // Change nothing
$a->varA = 'A';
$c->varA = 'C';

echo
$a->getParent(); // print Z
echo $a->getName(); // print B
echo $b->getName(); // print B
echo $c->getName(); // print C
echo $d->getName(); // print B
echo $z->getName(); // print B
echo $z->varA; // print A
echo $c->varA; // print C
?>
up
-7
shaun at slickdesign dot com dot au
4 years ago
Similar to functions, unless they are in conditionals, it is possible to define classes anywhere within your script and they still generate instances.

It is also possible to define child classes before the parent class, however, this seems to act the same way as a conditional, meaning that you need to define these classes before they can be used.

Examples:

- Standard usage (A and B are always accessible)
<?php
class A {}
class
B extends A {}

var_dump( class_exists( 'A' ), class_exists( 'B' ) );
// Outputs: bool(true) bool(true)
?>

- End of file declaration (A and B are still always accessible, even if you have a return or exit before it)
<?php
var_dump
( class_exists( 'A' ), class_exists( 'B' ) );
// Outputs: bool(true) bool(true)

die;
class
A {}
class
B extends A {}
?>

- Child before parent declaration (B is not accessible until it has been defined)
<?php
var_dump
( class_exists( 'A' ), class_exists( 'B' ) );
// Outputs: bool(true) bool(false)

class B extends A {}
var_dump( class_exists( 'B' ) );
// Outputs: bool(true)

class A {}
?>

- Conditional definition (Same as child before parent example above)
<?php
var_dump
( class_exists( 'A' ), class_exists( 'B' ) );
// Outputs: bool(true) bool(false)

if ( ! class_exists( 'B' ) ) {
    class
B extends A {}
}
var_dump( class_exists( 'B' ) );
// Outputs: bool(true)

class A {}
up
-14
ghoucine at gmail dot com
8 years ago
For multiple single inheretance to work the order of class definition is very important if you're going up more than two levels in inheretence.

This won't work:

<?php

class A extends B {}

class
B extends C {}

class
C {}

$A = new A;
?>
Running the code above will spit a fatal error (Fatal Error:Class 'B' not found)

A change in class definition order will fix this:

<?php

class A extends B {}

class
C {}

class
B extends C {}

$A = new A;
?>

If you're goin up just one level in inhertance though there shouldn't be any problem. So this code works too:

<?php

class A extends B {}

class
{}

$A = new A;

?>

I have no explanation as to why this is the case though.
up
-12
tim at web dot com
5 years ago
[Document:Main.php]
<?php
//
include("person.php");       
include(
"student.php");   
include(
"teacher.php");       
//-----Creating a object of the class "teacher"--------
$t1=new teacher();
$t1->name="Mustermann";
$t1->forename="Max";
$t1->email="max@mustermann.com";

echo
$t1->name.", ".$t1->forename.": ".$t1->email;
$t1->ID();

//-----Creating a object of the class "student"--------
$s1=new student();
$s1->name="Kevin";
$s1->forename="Alpha";

echo
$s1->name."; ".$s1->forename;
$s1->ID();
?>

//-------------------------------------------------------------------------------------------
[Document:person.php]
<?php
class person
{
 
//Attribute
 
public $name;
  public
$forename;
}
?>

//-------------------------------------------------------------------------------------------
[Document:teacher.php]
<?php
class teacher extends person    /
{
 
//Attribute
 
public $email;
 
//Function
 
public function ID()
  {
    echo
"<p>I am a teacher</p>"
  }
}
?>

//-------------------------------------------------------------------------------------------
[Document:student.php]
<?php
class student extends Person
{
 
//Attribute
  //Functionen
 
public function ID()
  {
    echo
"<p>I am a student</p>"
  }
}
?>
up
-6
clintonabco at gmail dot com
5 years ago
This page is not clear about the nature and specifics of Object Inheritance especially that you can only make the visibility of an inherited method or property weaker and not stronger within the subclass that is inheriting these from its parent class.

Example:

<?php
class Test1
{
    protected
$a_property = "This is a property";
   
    protected function
printProperty()
    {
        echo
$this->a_property;
    }
}

class
Test2 extends Test1
{
    private
$b_property = "This is another property";
   
    private function
printProperty()
    {
        echo
$this->b_property;
    }
}

$test2 = new Test2();
?>

This code produces a PHP Fatal error with message:

PHP Fatal error:  Access level to Test2::printProperty() must be protected (as in class Test1) or weaker

So if you inherit a protected method and you want redeclare it in your subclass then you can either declare its visibility as protected or public. If public is inherited then it stays public.

Here is the working version of the code snippet above:

<?php
class Test1
{
    protected
$a_property = "This is a property";
   
    protected function
printProperty()
    {
        echo
$this->a_property;
    }
}

class
Test2 extends Test1
{
    private
$b_property = "This is another property";
   
    public function
printProperty()
    {
        echo
$this->b_property;
    }
}

$test2 = new Test2();
$test2->printProperty();
?>

To iterate what the description on the page says, subclasses inherit all protected and public properties and methods.
up
-27
php at sleep is the enemy dot co dot uk
12 years ago
Here's fun, an attempt to make some degree of multiple inheritance work in PHP using mixins. It's not particularly pretty, doesn't support method visibility modifiers and, if put to any meaningful purpose, could well make your call stack balloon to Ruby-on-Rails-esque proportions, but it does work.

<?php
abstract class Mix {
   
    protected
$_mixMap = array();
   
    public function
__construct(){
       
        
$this->_mixMap = $this->collectMixins($this);
    }
   
    public function
__call($method, $args){
       
       
// doesn't pass scope
        //return call_user_func_array(array($className, $method), $args);
       
        // Error: Given object is not an instance of the class this method was declared in
        //$method = new ReflectionMethod($className, $method);
        //return $method->invokeArgs($this, $args);
       
       
$payload = $this->buildMixinPayload($this->_mixMap, $method, $args);
        if(!
$payload) throw new Exception('Method ' . $method . ' not found');
       
        list(
$mixinMethod, list($method, $args)) = $payload;
       
        return
$this->$mixinMethod($method, $args);
       
    }
   
    protected function
collectMixins($class){
       
        static
$found = array();
        static
$branch = array();
       
        if(empty(
$branch)) $branch[] = get_class($this);
       
$mixins = array();
       
        foreach(
array_reverse(get_class_methods($class)) as $method){
            if(
preg_match('/^mixin(\w+)$/', $method, $matches)){
               
               
$className = $matches[1];
               
                if(
in_array($className, $branch))
                    throw new
Exception('Circular reference detected ' . implode(' > ', $branch) . ' > ' . $className);
                   
                if(!
in_array($className, $found)){
               
                    if(!
class_exists($className)) throw new Exception('Class ' . $className . ' not found');
           
                   
// populate props from mixin class
                   
foreach(get_class_vars($className) as $key => $value){       
                        if(!
property_exists($this, $key)) $this->$key = $value;
                    }
                   
                   
$found[] = $branch[] = $className;               
                   
$mixins[$className] = $this->collectMixins($className);
                }
               
               
$branch = array(get_class($this));
            }
        }
       
        return
$mixins;
    }
   
    protected function
buildMixinPayload($mixins, $method, $args){
       
        foreach(
$mixins as $className => $parents){
           
           
$mixinMethod = 'mixin' . $className;
           
            if(
method_exists($className, $method)) return array($mixinMethod, array($method, $args));
           
            if(!empty(
$parents) && $return = $this->buildMixinPayload($parents, $method, $args)){
                return array(
$mixinMethod, $return);
            }
        }
       
        return
false;
    }
   
}
?>
up
-47
msg2maciej at aol dot com
11 years ago
PHP supports single class inheritance. My bare idea on accessing protected methods with power of abstracts and sort of "multi-class inheritance SIMULATION":

<?php
error_reporting
(E_ALL);

abstract class
Base {
    abstract protected function
__construct ();
    abstract protected function
hello_left ();
    abstract protected function
hello_right ();
}

abstract class
NotImplemented_Left extends Base {
protected function
hello_right () {
echo
'well, wont see that'; }}

abstract class
NotImplemented_Right extends Base {
protected function
hello_left () {
echo
'well, wont see that'; }}

class
Left extends NotImplemented_Left {
protected function
__construct () {        # limited visibility, no access from "outside"
echo __CLASS__.'::protected __construct'. "\n"; }
protected function
hello_left () {        # limited visibility, no access from "outside"
echo 'protected hello_left in ' . __CLASS__ . "\n"; }}

class
Right extends NotImplemented_Right {
protected function
__construct () {        # limited visibility, no access from "outside"
echo __CLASS__.'::protected __construct'. "\n"; }
protected function
hello_right () {        # limited visibility, no access from "outside"
echo 'protected hello_right in ' . __CLASS__ . "\n"; }
protected function
hello_left () {
echo
"wont see that, and easy to get rid of it from here\n"; }}

class
Center extends Base {
private
$left;
private
$right;
public function
__construct () {
echo
'welcome in ' . __CLASS__ . "\n";
echo
'Center::'; $this->left = new Left;
echo
'Center::'; $this->right = new Right;
echo
" oh and\n";
$this->hello_left();
$this->hello_right();
}
public function
hello_left () {            # calling class Left
echo __CLASS__.'::'; $this->left->hello_left(); }
public function
hello_right () {        # calling class Right
echo __CLASS__.'::'; $this->right->hello_right(); }
}

$c = new Center;
?>

Produces:

welcome in Center
Center::Left::protected __construct
Center::Right::protected __construct
oh and
Center::protected hello_left in Left
Center::protected hello_right in Right
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