Properties

Class member variables are called properties. You may also see them referred to using other terms such as attributes or fields, but for the purposes of this reference we will use properties. They are defined by using one of the keywords public, protected, or private, optionally followed by a type declaration, followed by a normal variable declaration. This declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

See Visibility for more information on the meanings of public, protected, and private.

Note:

In order to maintain backward compatibility with PHP 4, PHP 5 will still accept the use of the keyword var in property declarations instead of (or in addition to) public, protected, or private. However, var is no longer required. In versions of PHP from 5.0 to 5.1.3, the use of var was considered deprecated and would issue an E_STRICT warning, but since PHP 5.1.3 it is no longer deprecated and does not issue the warning.

If you declare a property using var instead of one of public, protected, or private, then PHP 5 will treat the property as if it had been declared as public.

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

The pseudo-variable $this is available inside any class method when that method is called from within an object context. $this is a reference to the calling object (usually the object to which the method belongs, but possibly another object, if the method is called statically from the context of a secondary object).

Example #1 property declarations

<?php
class SimpleClass
{
   // valid as of PHP 5.6.0:
   public $var1 = 'hello ' . 'world';
   // valid as of PHP 5.3.0:
   public $var2 = <<<EOD
hello world
EOD;
   // valid as of PHP 5.6.0:
   public $var3 = 1+2;
   // invalid property declarations:
   public $var4 = self::myStaticMethod();
   public $var5 = $myVar;

   // valid property declarations:
   public $var6 = myConstant;
   public $var7 = array(true, false);

   // valid as of PHP 5.3.0:
   public $var8 = <<<'EOD'
hello world
EOD;
}
?>

Note:

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

Heredoc and Nowdoc

As of PHP 5.3.0 heredocs and nowdocs can be used in any static data context, including property declarations.

Example #2 Example of using a nowdoc to initialize a property

<?php
class foo {
   // As of PHP 5.3.0
   public $bar = <<<'EOT'
bar
EOT;
   public $baz = <<<EOT
baz
EOT;
}
?>

Note:

Nowdoc and Heredoc support was added in PHP 5.3.0.

Type declarations

As of PHP 7.4.0, property definitions can include a type declaration.

Example #3 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);

?>

The above example will output:

int(1234)
NULL

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

Example #4 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());
?>

The above example will output:

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

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

Valid property types

Type Description Minimum PHP version
bool The property must be boolean value. PHP 7.4.0
int The property must be an integer. PHP 7.4.0
float The property must be a floating point number. PHP 7.4.0
string The property must be a string. PHP 7.4.0
array The property must be an array. PHP 7.4.0
object The property must be an object. PHP 7.4.0
iterable The property must be either an array or an instanceof Traversable. PHP 7.4.0
self The property must be an instanceof the same class in which the property is defined. PHP 7.4.0
parent The property must be an instanceof the parent class of the class in which the property is defined. PHP 7.4.0
Class/interface name The property must be an instanceof the given class or interface name. PHP 7.4.0
?type The property must be the specified type, or NULL. PHP 7.4.0