title: Source of method in Laravel
body: <p>In the source code of <code>Illuminate\Mail\PendingMail</code> (<a href="https://laravel.com/api/5.8/Illuminate/Mail/PendingMail.html" rel="nofollow noreferrer">API reference</a>), the <code>queue</code> method references <code>$this-&gt;mailer-&gt;queue</code>. However, <code>$this-&gt;mailer</code> is an instance of <code>Illuminate\Contracts\Mail\Mailer</code> (<a href="https://laravel.com/api/5.8/Illuminate/Contracts/Mail/Mailer.html" rel="nofollow noreferrer">API reference</a>) which has no <code>queue</code> method. So can anyone please explain how this piece of code works if it seemingly calls a method that doesn't exist?</p>