src/Viserio/Component/Mail/TransportFactory.php
public function extend(string $driver, Closure $callback): void
    {
        $this->extensions[$driver] = $callback->bindTo($this, $this);
    }
public function extend(string $driver, Closure $callback): void
    {
        $this->extensions[$driver] = $callback->bindTo($this, $this);
    }
{@inheritdoc}