Wordpress MVC - Add action legacy

doc.action.legacy.php

<?php
class Main extends Plugin
{
    public function init()
    {
        // This will call 'save_post' function located in Main class.
        add_action( 'save_post', [ &$this, 'save_post' ] );
    }
    
    // Callback handler for action 'save_post'.
    public function save_post()
    {
        // TODO CODE
    }
}