WordPress at a glance
function is not described

wpdb::__isset() public WP 3.5.0

Makes private properties check-able for backward compatibility.

{} It's a method of the class: wpdb{}

No Hooks.

Return

true/false. If the member is set or not.

Usage

global $wpdb;
$wpdb->__isset( $name );
$name(string) (required)
The private member to check.

Changelog

Since 3.5.0 Introduced.

Code of wpdb::__isset() WP 5.5.1

<?php
public function __isset( $name ) {
	return isset( $this->$name );
}