plugins_loaded

add_action( 'plugins_loaded', array( 'gcdocs_class_name', 'instance' ) );

class gcdocs_class_name {
	
	private function __construct() {
	        self::init();
	}
	
	public static function instance() {
		static $instance = null;

		if ( is_null( $instance ) ) {
			$instance = new class_name;
		}
		
		return $instance;
	}
	
	public function init() {
		gc_die( __( 'Hello World!', 'text-domain' ) );
	}
	
}