WP_Widget_Factory::register( string|WP_Widget $widget )

Source

File: wp-includes/class-wp-widget-factory.php

public function register( $widget ) {
		if ( $widget instanceof WP_Widget ) {
			$this->widgets[ spl_object_hash( $widget ) ] = $widget;
		} else {
			$this->widgets[ $widget ] = new $widget();
		}
	}