PHP Tutorial · Object-Oriented PHP · Lesson 33 of 38

PHP Traits and Static Members

Reuse methods with traits and use class-level static properties and methods.

Traits

A trait is a bundle of methods you can use in several unrelated classes — horizontal code reuse without inheritance:

Example 1Try it yourself

<?php
trait HasTimestamps
{
    private ?string $updatedAt = null;

    public function touch(string $when): static
    {
        $this->updatedAt = $when;
        return $this;
    }

    public function updatedAt(): ?string
    {
        return $this->updatedAt;
    }
}

class Post { use HasTimestamps; }
class Comment { use HasTimestamps; }

echo (new Post())->touch("2026-10-12")->updatedAt(), "\n";
var_dump((new Comment())->updatedAt());

Output

2026-10-12
NULL

Static properties and methods

static members belong to the class, not to an object. Access them with ClassName:: or self:: / static:: inside the class. Common uses: counters, factory methods and constants.

Example 2Try it yourself

<?php
class Order
{
    public const STATUS_NEW = "new";
    private static int $created = 0;

    private function __construct(public readonly int $id, public readonly string $status) {}

    public static function create(): static
    {
        self::$created++;
        return new static(self::$created, self::STATUS_NEW);
    }

    public static function count(): int
    {
        return self::$created;
    }
}

$a = Order::create();
$b = Order::create();
echo "Order #{$b->id} is {$b->status}; total created: ", Order::count(), "\n";

Output

Order #2 is new; total created: 2

Use static state sparingly — it's global state in disguise and makes testing harder.

Test yourself

Which keyword pulls a trait into a class?

include
extends
use
implements

Show answer

Answer: use