haphpiness

Late Static Binding

Late static binding (static:: vs self::) lets parent classes defer method resolution to the child class. It's the foundation of the fluent factory pattern used by every modern PHP framework.

class Model {
    protected static string $table;

    // self:: would always resolve to Model — wrong!
    // static:: resolves to whatever class called the method
    public static function find(int $id): static {
        $table = static::$table;
        $row = DB::query("SELECT * FROM {$table} WHERE id = ?", [$id]);
        return static::hydrate($row);  // Returns User, not Model
    }

    public static function create(array $data): static {
        // static:: ensures the child class is instantiated
        $instance = new static();
        foreach ($data as $key => $value) {
            $instance->$key = $value;
        }
        $instance->save();
        return $instance;
    }
}

class User extends Model {
    protected static string $table = 'users';
}

class Post extends Model {
    protected static string $table = 'posts';
}

$user = User::find(1);    // Returns User instance, queries 'users' table
$post = Post::create([    // Returns Post instance
    'title' => 'Hello',
]);

The static return type (PHP 8.0) completed this feature by letting you declare that a method returns an instance of the called class, not the declaring class. This is what makes fluent builder patterns type-safe.