Properties

Properties

Class member variables are called . They may be referred to using other terms such as , but for the purposes of this reference will be used. They are defined by using at least one modifier (such as , , or, as of PHP 8.1.0, ), optionally (except for properties), as of PHP 7.4, followed by a type declaration, followed by a normal variable declaration. This declaration may include an initialization, but this initialization must be a value. propertiesfieldspropertiesreadonlyreadonlyconstant

Opmerking: > An obsolete way of declaring class properties, is by using the keyword instead of a modifier. var

Opmerking: > A property declared without a modifier will be declared as . public

Within class methods non-static properties may be accessed by using (Object Operator):
(where is the name of the property). Static properties are accessed by using the (Double Colon): . See for more information on the difference between static and non-static properties. ->``$this->property``property``::``self::$property

The pseudo-variable is available inside any class method when that method is called from within an object context. is the value of the calling object. $this``$this

Voorbeeld: Property declarations

<?php
class SimpleClass
{
   public $var1 = 'hello ' . 'world';
   public $var2 = <<<EOD
hello world
EOD;
   public $var3 = 1+2;
   // invalid property declarations:
   public $var4 = self::myStaticMethod();
   public $var5 = $myVar;

   // valid property declarations:
   public $var6 = myConstant;
   public $var7 = [true, false];

   public $var8 = <<<'EOD'
hello world
EOD;

   // Without visibility modifier:
   static $var9;
   readonly int $var10;
}
?>

Opmerking: > There are various functions to handle classes and objects. See the reference. Class/Object Functions

Type declarations

As of PHP 7.4.0, property definitions can include
,
with the exception of .

callableVoorbeeld: Example of typed properties

<?php

class User
{
    public int $id;
    public ?string $name;

    public function __construct(int $id, ?string $name)
    {
        $this->id = $id;
        $this->name = $name;
    }
}

$user = new User(1234, null);

var_dump($user->id);
var_dump($user->name);

?>

int(1234)
NULL

Typed properties must be initialized before accessing, otherwise an
 is thrown.

ErrorVoorbeeld: Accessing properties

<?php

class Shape
{
    public int $numberOfSides;
    public string $name;

    public function setNumberOfSides(int $numberOfSides): void
    {
        $this->numberOfSides = $numberOfSides;
    }

    public function setName(string $name): void
    {
        $this->name = $name;
    }

    public function getNumberOfSides(): int
    {
        return $this->numberOfSides;
    }

    public function getName(): string
    {
        return $this->name;
    }
}

$triangle = new Shape();
$triangle->setName("triangle");
$triangle->setNumberofSides(3);
var_dump($triangle->getName());
var_dump($triangle->getNumberOfSides());

$circle = new Shape();
$circle->setName("circle");
var_dump($circle->getName());
var_dump($circle->getNumberOfSides());
?>

string(8) "triangle"
int(3)
string(6) "circle"

Fatal error: Uncaught Error: Typed property Shape::$numberOfSides must not be accessed before initialization

Readonly properties

As of PHP 8.1.0, a property can be declared with the  modifier,
which prevents modification of the property after initialization.  Prior to PHP 8.4.0
a  property is implicitly private-set, and may only be written to
from the same class.  As of PHP 8.4.0,  properties are implicitly
,
so may be set from child classes.  That may be overridden
explicitly if desired.

readonly``readonly``readonlyprotected(set)Voorbeeld: Example of readonly properties

<?php

class Test {
   public readonly string $prop;

   public function __construct(string $prop) {
       // Legal initialization.
       $this->prop = $prop;
   }
}

$test = new Test("foobar");
// Legal read.
var_dump($test->prop); // string(6) "foobar"

// Illegal reassignment. It does not matter that the assigned value is the same.
$test->prop = "foobar";
// Error: Cannot modify readonly property Test::$prop
?>

Opmerking: > The readonly modifier can only be applied to . A readonly property without type constraints can be created using the type. typed properties

Opmerking: > Readonly static properties are not supported.

A readonly property can only be initialized once, and only from the scope where it has been declared. Any other assignment or modification of the property will result in an  exception.

ErrorVoorbeeld: Illegal initialization of readonly properties

<?php
class Test1 {
    public readonly string $prop;
}

$test1 = new Test1;
// Illegal initialization outside of private scope.
$test1->prop = "foobar";
// Error: Cannot initialize readonly property Test1::$prop from global scope
?>

Opmerking: > Specifying an explicit default value on readonly properties is not allowed, because a readonly property with a default value is essentially the same as a constant, and thus not particularly useful.

```php

Opmerking: > Readonly properties cannot be once they are initialized. However, it is possible to unset a readonly property prior to initialization, from the scope where the property has been declared. unset

Modifications are not necessarily plain assignments, all of the following will also result in an  exception:

`Error````php

i += 1; $test->i++; ++$test->i; $test->ary[] = 1; $test->ary[0][] = 1; unset($test->ary[0]); $ref =& $test->i; $test->i =& $ref; byRef($test->i); foreach ($test as &$prop); ?>

    However, readonly properties do not preclude interior mutability. Objects (or resources) stored in readonly properties may still be modified internally:
    
   ```php
<?php

class Test {
    public function __construct(public readonly object $obj) {}
}

$test = new Test(new stdClass);
// Legal interior mutation.
$test->obj->foo = 1;
// Illegal reassignment.
$test->obj = new stdClass;
?>

As of PHP 8.3.0, readonly properties can be reinitialized when cloning an object
using the  method.

__clone()Voorbeeld: Readonly properties and cloning

<?php
class Test1 {
    public readonly ?string $prop;

    public function __clone() {
        $this->prop = null;
    }

    public function setProp(string $prop): void {
        $this->prop = $prop;
    }
}

$test1 = new Test1;
$test1->setProp('foobar');

$test2 = clone $test1;
var_dump($test2->prop); // NULL
?>

Dynamic properties

If trying to assign to a non-existent property on an object,
PHP will automatically create a corresponding property.
This dynamically created property will  be
available on this class instance.

only

Waarschuwing: > Dynamic properties are deprecated as of PHP 8.2.0. It is recommended to declare the property instead. To handle arbitrary property names, the class should implement the magic methods and . At last resort the class can be marked with the attribute. __get()__set()#[\AllowDynamicProperties]