Helpers/aliases to avoid notices when transitioning from TEC 3.9.x -> 3.10/4.x

tec-extensions-transition.php

<?php
/**
 * Provides access to the main TEC object.
 * 
 * @return TribeEvents|Tribe__Events__Events
 */
function prefix_get_event_instance() {
	static $instance;

	if ( ! isset( $instance ) && class_exists( 'Tribe__Events__Events' ) ) {
		$instance = Tribe__Events__Events::instance();
	}
	elseif ( ! isset( $instance ) && class_exists( 'TribeEvents' ) ) {
		$instance = TribeEvents::instance();
	}
	
	return $instance;
}

/**
 * Provides notice-free access to TribeEvents/Tribe__Events__Events 
 * class constants, etc.
 */
if ( class_exists( 'Tribe__Events__Events' ) ) {
	class Prefix_Event_Class extends Tribe__Events__Events {}
}
elseif ( class_exists( 'TribeEvents' ) ) {
	class Prefix_Event_Class extends TribeEvents {}
}