How may I restore the classic content editor in WordPress 5+?

In WordPress version above 5.0 we will experience a new content editor (gutenberg). If you want it, you can easily go back to the previous one by adding the appropriate code in the functions.php file of your theme. Just go and edit the file on your server: /wp-content/themes/name_of_your_theme/functions.php and add the following code:

if ( version_compare($GLOBALS['wp_version'], '5.0-beta', '>') ) {
    // WP > 5 beta
    add_filter( 'use_block_editor_for_post_type', '__return_false', 100 );
} else {
    // WP < 5 beta
    add_filter( 'gutenberg_can_edit_post_type', '__return_false' );
}

Voilà 🙂