Modifiers

Last updated: April 6, 2026 Minimum PHP Version: PHP 5.0+ Status: Stable

There are three access modifiers:

1. public - the property or method can be accessed from everywhere. This is default
2. protected - the property or method can be accessed within the class and by classes derived from that class
3. private - the property or method can ONLY be accessed within the class

<?php
class Fruit {
  public $name;
  protected $color;
  private $weight;
}

$mango = new Fruit();
$mango->name = 'Mango'; // OK
$mango->color = 'Yellow'; // ERROR
$mango->weight = '300'; // ERROR
?>

<?php
class Fruit {
  public $name;
  public $color;
  public $weight;

  function set_name($n) {  // a public function (default)
    $this->name = $n;
  }
  protected function set_color($n) { // a protected function
    $this->color = $n;
  }
  private function set_weight($n) { // a private function
    $this->weight = $n;
  }
}

$mango = new Fruit();
$mango->set_name('Mango'); // OK
$mango->set_color('Yellow'); // ERROR
$mango->set_weight('300'); // ERROR
?>

Readonly Properties (PHP 8.1+)

The readonly modifier prevents a property from being modified after initialization. This is useful for immutability patterns.

<?php
class Config
{
    public function __construct(
        public readonly string $host,
        public readonly int $port,
        public readonly string $name
    ) {}
}

$config = new Config('localhost', 3306, 'myapp');
echo $config->host; // OK - reading
$config->host = 'example.com'; // ERROR - cannot modify
?>

With Constructor Property Promotion

<?php
class User
{
    public function __construct(
        public readonly int $id,
        public readonly string $name,
        public readonly string $email,
        public readonly DateTimeImmutable $createdAt
    ) {}
}

$user = new User(1, 'John', 'john@example.com', new DateTimeImmutable());
$user->name = 'Jane'; // ERROR - cannot modify readonly property
?>

Initialization Rules

<?php
class Example
{
    public readonly string $value;

    public function __construct(string $value)
    {
        $this->value = $value;
    }
}

$ex = new Example('test');
$ex->value = 'changed'; // ERROR - cannot modify after initialization
?>

Difference from const

Feature	const	readonly
Value set at	Compile time	Runtime (construction)
Can be dynamic	No	Yes
Per-instance	No (static)	Yes
Type flexible	Limited	All types