trait / Magic Methods Since: PHP 5.4（2012）

// Define a trait.
trait TraitName {
	public function method() { }
}

// Mix the trait into a class.
class ClassName {
	use TraitName;
}

// Check an object's type with instanceof.
$obj instanceof ClassName;

<?php
// Basic trait usage.
trait Timestampable {
	private string $created_at;
	private string $updated_at;

	public function set_timestamps(): void {
		$now = date('Y-m-d H:i:s');
		$this->created_at = $this->created_at ?? $now;
		$this->updated_at = $now;
	}

	public function get_created_at(): string {
		return $this->created_at;
	}
}

trait SoftDeletable {
	private ?string $deleted_at = null;

	public function soft_delete(): void {
		$this->deleted_at = date('Y-m-d H:i:s');
	}

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

// Using multiple traits together.
class Post {
	use Timestampable, SoftDeletable;

	public function __construct(
		public string $title
	) {
		$this->set_timestamps();
	}
}

$post = new Post("Intro to PHP Traits");
echo $post->get_created_at(); // Outputs the current date and time.
$post->soft_delete();
var_dump($post->is_deleted()); // Outputs 'bool(true)'.

// Example of the __toString() magic method.
class Money {
	public function __construct(
		private int $amount,
		private string $currency = 'USD'
	) {}

	public function __toString(): string {
		return number_format($this->amount) . $this->currency;
	}
}

$price = new Money(2980);
echo $price; // Outputs '2,980USD'. __toString() is called automatically.

// Example of __get() and __set().
class FlexibleObject {
	private array $data = [];

	public function __get(string $name): mixed {
		return $this->data[$name] ?? null;
	}

	public function __set(string $name, mixed $value): void {
		$this->data[$name] = $value;
	}
}

$obj = new FlexibleObject();
$obj->color = "red";  // __set() is called.
echo $obj->color;     // __get() is called, outputs 'red'.

// Example of __invoke().
class Multiplier {
	public function __construct(
		private int $factor
	) {}

	public function __invoke(int $value): int {
		return $value * $this->factor;
	}
}

$double = new Multiplier(2);
echo $double(5);  // Outputs '10'. The object is called like a function.
echo $double(15); // Outputs '30'.

// Checking types with instanceof.
var_dump($post instanceof Post);          // Outputs 'bool(true)'.
var_dump($price instanceof Money);        // Outputs 'bool(true)'.
var_dump($price instanceof \Stringable);  // Outputs 'bool(true)' because __toString() is defined.

Traits were introduced in PHP 5.4 as a way to reuse code across classes. Because PHP supports only single inheritance, a class cannot inherit from multiple parent classes — but traits let you freely mix in multiple sets of functionality. They are well suited for common behaviors shared across many classes, such as managing timestamps, soft deletes, or logging.

Magic methods are special methods that PHP calls automatically in specific situations. __toString() defines the string representation of an object. __get() and __set() control dynamic property access. Defining __invoke() lets you call an object like a function, which is handy when passing it as a callback.

For the basics of classes, see class. For inheritance and interfaces, see extends / implements.