public function add( $args, $assoc_args ) {
		list( $key, $value, $group, $expiration ) = $args;

		if ( ! wp_cache_add( $key, $value, $group, $expiration ) ) {
			WP_CLI::error( "Could not add object '$key' in group '$group'. Does it already exist?" );
		}

		WP_CLI::success( "Added object '$key' in group '$group'." );
	}