CMB2 has a clever way of handling the same situation. It establishes a version constant that is a high number for the first release (9999), and on each subsequent release, the version constant is decremented. The version number is used for the priority of the action that instantiates the main class. This ensures that the most recent version of the library is loaded.
From CMB2’s init.php
if ( ! class_exists( 'CMB2_Bootstrap_212', false ) ) {
/**
* Handles checking for and loading the newest version of CMB2
*
* @since 2.0.0
*
* @category WordPress_Plugin
* @package CMB2
* @author WebDevStudios
* @license GPL-2.0+
* @link http://webdevstudios.com
*/
class CMB2_Bootstrap_212 {
/**
* Current version number
* @var string
* @since 1.0.0
*/
const VERSION = '2.1.2';
/**
* Current version hook priority.
* Will decrement with each release
*
* @var int
* @since 2.0.0
*/
const PRIORITY = 9987;
/**
* Single instance of the CMB2_Bootstrap_212 object
*
* @var CMB2_Bootstrap_212
*/
public static $single_instance = null;
/**
* Creates/returns the single instance CMB2_Bootstrap_212 object
*
* @since 2.0.0
* @return CMB2_Bootstrap_212 Single instance object
*/
public static function initiate() {
if ( null === self::$single_instance ) {
self::$single_instance = new self();
}
return self::$single_instance;
}
/**
* Starts the version checking process.
* Creates CMB2_LOADED definition for early detection by other scripts
*
* Hooks CMB2 inclusion to the init hook on a high priority which decrements
* (increasing the priority) with each version release.
*
* @since 2.0.0
*/
private function __construct() {
/**
* A constant you can use to check if CMB2 is loaded
* for your plugins/themes with CMB2 dependency
*/
if ( ! defined( 'CMB2_LOADED' ) ) {
define( 'CMB2_LOADED', true );
}
add_action( 'init', array( $this, 'include_cmb' ), self::PRIORITY );
}
/**
* A final check if CMB2 exists before kicking off our CMB2 loading.
* CMB2_VERSION and CMB2_DIR constants are set at this point.
*
* @since 2.0.0
*/
public function include_cmb() {
if ( class_exists( 'CMB2', false ) ) {
return;
}
if ( ! defined( 'CMB2_VERSION' ) ) {
define( 'CMB2_VERSION', self::VERSION );
}
if ( ! defined( 'CMB2_DIR' ) ) {
define( 'CMB2_DIR', trailingslashit( dirname( __FILE__ ) ) );
}
$this->l10ni18n();
// Include helper functions
require_once 'includes/helper-functions.php';
// Now kick off the class autoloader
spl_autoload_register( 'cmb2_autoload_classes' );
// Kick the whole thing off
require_once 'bootstrap.php';
}
/**
* Registers CMB2 text domain path
* @since 2.0.0
*/
public function l10ni18n() {
$loaded = load_plugin_textdomain( 'cmb2', false, '/languages/' );
if ( ! $loaded ) {
$loaded = load_muplugin_textdomain( 'cmb2', '/languages/' );
}
if ( ! $loaded ) {
$loaded = load_theme_textdomain( 'cmb2', get_stylesheet_directory() . '/languages/' );
}
if ( ! $loaded ) {
$locale = apply_filters( 'plugin_locale', get_locale(), 'cmb2' );
$mofile = dirname( __FILE__ ) . '/languages/cmb2-' . $locale . '.mo';
load_textdomain( 'cmb2', $mofile );
}
}
}
// Make it so...
CMB2_Bootstrap_212::initiate();
}