public static function instance()
 {
     if (!self::$instance) {
         self::$instance = new self();
     }
     return self::$instance;
 }
<?php

/*
Plugin Name: WordPress Front-end Editor
Plugin URI: http://wordpress.org/plugins/wp-front-end-editor/
Description: WordPress Front-end Editor
Author: avryl
Author URI: http://profiles.wordpress.org/avryl/
Version: 0.9.1
Text Domain: wp-front-end-editor
License: GPLv2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html
*/
if (!class_exists('WP_Front_End_Editor')) {
    require_once 'class-wp-front-end-editor.php';
    WP_Front_End_Editor::instance();
}