Type Declarations in Classes

<?php
declare(strict_types=1);

class Invoice
{
    public function __construct(
        private int $id,
        private float $amount,
        private ?string $note = null,
    ) {}

    public function summary(): string
    {
        return "Invoice #{$this->id}: " . number_format($this->amount, 2);
    }
}

echo (new Invoice(7, 1234.5))->summary();

Invoice #7: 1,234.50

<?php
class Customer
{
    public function __construct(public string $name) {}
}

class Order
{
    public function __construct(private Customer $customer) {}

    public function describe(): string
    {
        return "Order for " . $this->customer->name;
    }
}

echo (new Order(new Customer("Ana")))->describe();

Order for Ana

<?php
class Customer {}

function show(Customer $c): string
{
    return "ok";
}

try {
    show("Ana");
} catch (TypeError $e) {
    echo substr($e->getMessage(), 0, 52);
}

show(): Argument #1 ($c) must be of type Customer, s

<?php
class Money
{
    public function __construct(public readonly int $cents) {}

    public function plus(Money $other): self
    {
        return new self($this->cents + $other->cents);
    }
}

echo (new Money(150))->plus(new Money(250))->cents;

400

<?php
interface Shape
{
    public function area(): float;
}

class Square implements Shape
{
    public function __construct(private float $side) {}

    public function area(): float
    {
        return $this->side ** 2;
    }
}

function printArea(Shape $shape): void
{
    echo "Area: " . $shape->area();
}

printArea(new Square(3));

Area: 9

<?php
class Logger {}

class Service
{
    public function __construct(private ?Logger $logger = null) {}

    public function hasLogger(): bool
    {
        return $this->logger !== null;
    }
}

var_dump((new Service())->hasLogger());

bool(false)

<?php
class Cart
{
    /** @var Product[] */
    private array $items = [];
}