Just a quick note that it's possible to declare visibility for multiple properties at the same time, by separating them by commas.
eg:
<?php
class a
{
protected $a, $b;
public $c, $d;
private $e, $f;
}
?>
Die Sichtbarkeit einer Eigenschaft, Methode oder (von PHP 7.1.0 an) einer Konstante kann definiert werden, indem
man der Deklaration eines der Schlüsselwörter public,
protected oder private voranstellt.
Auf public deklarierte Elemente kann von überall her zugegriffen werden.
Protected beschränkt den Zugang auf Elternklassen und abgeleitete Klassen
(sowie die Klasse, die das Element definiert). Private grenzt die Sichtbarkeit
einzig auf die Klasse ein, die das Element definiert.
Klasseneigenschaften können als public, private oder protected definiert werden. Eigenschaften, die ohne explizites Schlüsselwort für die Sichtbarkeit deklariert sind, werden als public definiert.
Beispiel #1 Eigenschaftendeklaration
<?php
/**
* Definiere MyClass
*/
class MyClass
{
public $public = 'Public';
protected $protected = 'Protected';
private $private = 'Private';
function printHello()
{
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj = new MyClass();
echo $obj->public; // Funktioniert
echo $obj->protected; // Fataler Fehler
echo $obj->private; // Fataler Fehler
$obj->printHello(); // Zeigt Public, Protected und Private
/**
* Definiere MyClass2
*/
class MyClass2 extends MyClass
{
// Wir können die public- und protected-Eigenschaften neu deklarieren,
// aber nicht die private
public $public = 'Public2';
protected $protected = 'Protected2';
function printHello()
{
echo $this->public;
echo $this->protected;
echo $this->private;
}
}
$obj2 = new MyClass2();
echo $obj2->public; // Funktioniert
echo $obj2->protected; // Fataler Fehler
echo $obj2->private; // Undefiniert
$obj2->printHello(); // Zeigt Public2, Protected2, Undefined
?>
As of PHP 8.4, properties may also have their
visibility set asymmetrically, with a different scope for
reading (get) and writing (set).
Specifically, the set visibility may be
specified separately, provided it is not more permissive than the
default visibility.
Beispiel #2 Asymmetric Property visibility
<?php
class Book
{
public function __construct(
public private(set) string $title,
public protected(set) string $author,
protected private(set) int $pubYear,
) {}
}
class SpecialBook extends Book
{
public function update(string $author, int $year): void
{
$this->author = $author; // OK
$this->pubYear = $year; // Fatal Error
}
}
$b = new Book('How to PHP', 'Peter H. Peterson', 2024);
echo $b->title; // Works
echo $b->author; // Works
echo $b->pubYear; // Fatal Error
$b->title = 'How not to PHP'; // Fatal Error
$b->author = 'Pedro H. Peterson'; // Fatal Error
$b->pubYear = 2023; // Fatal Error
?>There are a few caveats regarding asymmetric visibility:
set visibility.
set visibility must be the same
as get or more restrictive. That is,
public protected(set) and protected protected(set)
are allowed, but protected public(set) will cause a syntax error.
public, then the main visibility may be
omitted. That is, public private(set) and private(set)
will have the same result.
private(set) visibility
is automatically final, and may not be redeclared in a child class.
set visibility, not get.
That is because a reference may be used to modify the property value.
get and
set operation internally, and therefore will follow the set
visibility, as that is always the more restrictive.
When a class extends another, the child class may redefine
any property that is not final. When doing so,
it may widen either the main visibility or the set
visibility, provided that the new visibility is the same or wider
than the parent class. However, be aware that if a private
property is overridden, it does not actually change the parent's property
but creates a new property with a different internal name.
Beispiel #3 Asymmetric Property inheritance
<?php
class Book
{
protected string $title;
public protected(set) string $author;
protected private(set) int $pubYear;
}
class SpecialBook extends Book
{
public protected(set) $title; // OK, as reading is wider and writing the same.
public string $author; // OK, as reading is the same and writing is wider.
public protected(set) int $pubYear; // Fatal Error. private(set) properties are final.
}
?>Klassenmethoden müssen mit public, private oder protected definiert werden. Methoden ohne jede explizite Deklaration sind als public definiert.
Beispiel #4 Methodendeklaration
<?php
/**
* Definiere MyClass
*/
class MyClass
{
// Deklariert einen public Konstruktor
public function __construct() { }
// Deklariere eine public Funktion
public function MyPublic() { }
// Deklariere eine protected Funktion
protected function MyProtected() { }
// Deklariere eine private Funktion
private function MyPrivate() { }
// Dies ist public
function Foo()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate();
}
}
$myclass = new MyClass;
$myclass->MyPublic(); // Funktioniert
$myclass->MyProtected(); // Fataler Fehler
$myclass->MyPrivate(); // Fataler Fehler
$myclass->Foo(); // Public, Protected und Private funktionieren
/**
* Definiere MyClass2
*/
class MyClass2 extends MyClass
{
// Dies ist public
function Foo2()
{
$this->MyPublic();
$this->MyProtected();
$this->MyPrivate(); // Fataler Fehler
}
}
$myclass2 = new MyClass2;
$myclass2->MyPublic(); // Funktioniert
$myclass2->Foo2(); // Public und Protected funktionieren, Private nicht
class Bar
{
public function test() {
$this->testPrivate();
$this->testPublic();
}
public function testPublic() {
echo "Bar::testPublic\n";
}
private function testPrivate() {
echo "Bar::testPrivate\n";
}
}
class Foo extends Bar
{
public function testPublic() {
echo "Foo::testPublic\n";
}
private function testPrivate() {
echo "Foo::testPrivate\n";
}
}
$myFoo = new Foo();
$myFoo->test(); // Bar::testPrivate
// Foo::testPublic
?>Von PHP 7.1.0 an können Klassenkonstanten als public, private, oder protected definiert werden. Konstanten, die ohne eine explizite Sichtbarkeitsangabe deklariert wurden, sind public.
Beispiel #5 Konstantendeklaration von PHP 7.1.0 an
<?php
/**
* Definiere MyClass
*/
class MyClass
{
// Deklariere eine öffentliche Konstante
public const MY_PUBLIC = 'öffentlich';
// Deklariere eine geschützte Konstante
protected const MY_PROTECTED = 'geschützt';
// Deklariere eine private Konstante
private const MY_PRIVATE = 'privat';
public function foo()
{
echo self::MY_PUBLIC;
echo self::MY_PROTECTED;
echo self::MY_PRIVATE;
}
}
$myclass = new MyClass();
MyClass::MY_PUBLIC; // funktioniert
MyClass::MY_PROTECTED; // fataler Fehler
MyClass::MY_PRIVATE; // fataler Fehler
$myclass->foo(); // öffentlich, geschützt und private funktioniert
/**
* Definiere MyClass2
*/
class MyClass2 extends MyClass
{
// Dies ist öffentlich
function foo2()
{
echo self::MY_PUBLIC;
echo self::MY_PROTECTED;
echo self::MY_PRIVATE; // fataler Fehler
}
}
$myclass2 = new MyClass2;
echo MyClass2::MY_PUBLIC; // funktioniert
$myclass2->foo2(); // öffentlich und geschützt funktioniert, aber nicht privat
?>Objekte des gleichen Types haben untereinander Zugriff auf die als private und protected markierten Member, obwohl es sich nicht um die gleichen Instanzen handelt. Dies liegt daran, dass die Details über die Implementierung innerhalb solcher Objekte bekannt sind.
Beispiel #6 Zugriff auf als private markierte Member des gleichen Objekttyps
<?php
class Test
{
private $foo;
public function __construct($foo)
{
$this->foo = $foo;
}
private function bar()
{
echo 'Zugriff auf die private Methode';
}
public function baz(Test $other)
{
// Ändern der privaten Eigenschaft ist möglich:
$other->foo = 'Hallo';
var_dump($other->foo);
// Aufruf der privaten Methode ist ebenfalls möglich:
$other->bar();
}
}
$test = new Test('test');
$test->baz(new Test('other'));
?>Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
string(5) "Hallo" Zugriff auf die private Methode +
Just a quick note that it's possible to declare visibility for multiple properties at the same time, by separating them by commas.
eg:
<?php
class a
{
protected $a, $b;
public $c, $d;
private $e, $f;
}
?>Dynamic properties are "public".
<?php
class MyClass {
public function setProperty($value) {
$this->dynamicProperty = $value;
}
}
$obj = new MyClass();
$obj->setProperty('Hello World');
echo $obj->dynamicProperty; // Outputs "Hello World"
?>
This usage is the same as well:
<?php
class MyClass {
}
$obj = new MyClass();
$obj->dynamicProperty = 'Hello World';
echo $obj->dynamicProperty; // Outputs "Hello World"
?>if not overwritten, self::$foo in a subclass actually refers to parent's self::$foo
<?php
class one
{
protected static $foo = "bar";
public function change_foo($value)
{
self::$foo = $value;
}
}
class two extends one
{
public function tell_me()
{
echo self::$foo;
}
}
$first = new one;
$second = new two;
$second->tell_me(); // bar
$first->change_foo("restaurant");
$second->tell_me(); // restaurant
?>> Members declared protected can be accessed only within
> the class itself and by inherited classes. Members declared
> as private may only be accessed by the class that defines
> the member.
This is not strictly true. Code outside the object can get and set private and protected members:
<?php
class Sealed { private $value = 'foo'; }
$sealed = new Sealed;
var_dump($sealed); // private $value => string(3) "foo"
call_user_func(\Closure::bind(
function () use ($sealed) { $sealed->value = 'BAZ'; },
null,
$sealed
));
var_dump($sealed); // private $value => string(3) "BAZ"
?>
The magic lay in \Closure::bind, which allows an anonymous function to bind to a particular class scope. The documentation on \Closure::bind says:
> If an object is given, the type of the object will be used
> instead. This determines the visibility of protected and
> private methods of the bound object.
So, effectively, we're adding a run-time setter to $sealed, then calling that setter. This can be elaborated to generic functions that can force set and force get object members:
<?php
function force_set($object, $property, $value) {
call_user_func(\Closure::bind(
function () use ($object, $property, $value) {
$object->{$property} = $value;
},
null,
$object
));
}
function force_get($object, $property) {
return call_user_func(\Closure::bind(
function () use ($object, $property) {
return $object->{$property};
},
null,
$object
));
}
force_set($sealed, 'value', 'quux');
var_dump(force_get($sealed, 'value')); // 'quux'
?>
You should probably not rely on this ability for production quality code, but having this ability for debugging and testing is handy.I couldn't find this documented anywhere, but you can access protected and private member varaibles in different instance of the same class, just as you would expect
i.e.
<?php
class A
{
protected $prot;
private $priv;
public function __construct($a, $b)
{
$this->prot = $a;
$this->priv = $b;
}
public function print_other(A $other)
{
echo $other->prot;
echo $other->priv;
}
}
class B extends A
{
}
$a = new A("a_protected", "a_private");
$other_a = new A("other_a_protected", "other_a_private");
$b = new B("b_protected", "ba_private");
$other_a->print_other($a); //echoes a_protected and a_private
$other_a->print_other($b); //echoes b_protected and ba_private
$b->print_other($a); //echoes a_protected and a_private
?>I see we can redeclare private properties into child class
<?php
class A{
private int $private_prop = 4;
protected int $protected_prop = 8;
}
class B extends A{
private int $private_prop = 7; // we can redeclare private property!!!
public function printAll() {
echo $this->private_prop;
echo $this->protected_prop;
}
}
$b = new B;
$b->printAll(); // show 78
}
?>