Properties

<?php
class Product
{
    public string $name = "Unnamed";
    public float $price = 0.0;
    public int $stock = 0;
}

$p = new Product();
$p->name = "Notebook";
$p->price = 80.5;

echo "{$p->name} costs {$p->price}";

Notebook costs 80.5

<?php
class Product
{
    public int $stock = 0;
}

$p = new Product();

try {
    $p->stock = "many";
} catch (TypeError $e) {
    echo $e->getMessage();
}

Cannot assign string to property Product::$stock of type int

public array $tags = [];
public string $status = "draft";
public ?string $note = null;
// public int $created = time();   // not allowed

<?php
class User
{
    public string $name = "";
    public ?string $phone = null;
}

$u = new User();

var_dump($u->phone);

NULL

<?php
class User
{
    public string $name;
}

$u = new User();

try {
    echo $u->name;
} catch (Error $e) {
    echo $e->getMessage();
}

Typed property User::$name must not be accessed before initialization

<?php
class Order
{
    public function __construct(public readonly int $id) {}
}

$order = new Order(1042);

try {
    $order->id = 7;
} catch (Error $e) {
    echo $e->getMessage();
}

Cannot modify readonly property Order::$id

<?php
class Point
{
    public int $x = 1;
    public int $y = 2;
}

print_r(get_object_vars(new Point()));

Array
(
    [x] => 1
    [y] => 2
)

<?php
class Box
{
    public ?int $size = null;
}

$box = new Box();

var_dump(isset($box->size));
var_dump(property_exists($box, "size"));

bool(false)
bool(true)