function bbp_exclude_forum_ids( $type = 'string' ) {

	// Setup arrays
	$forum_ids = array();

	// Types
	$types = array(
		'array'      => array(),
		'string'     => '',
		'meta_query' => array()
	);

	// Exclude for everyone but keymasters
	if ( ! bbp_is_user_keymaster() ) {

		// Get forum IDs to exclude
		$forum_ids = bbp_get_excluded_forum_ids();

		// Store return values in static types array
		if ( ! empty( $forum_ids ) ) {

			// Comparison
			$compare = ( 1 < count( $forum_ids ) )
				? 'NOT IN'
				: '!=';

			// Setup types
			$types['array']      = $forum_ids;
			$types['string']     = implode( ',', $forum_ids );
			$types['meta_query'] = array(
				'key'     => '_bbp_forum_id',
				'value'   => $types['string'],
				'type'    => 'NUMERIC',
				'compare' => $compare
			);
		}
	}

	// There are forums that need to be excluded
	$retval = $types[ $type ];

	// Filter & return
	return apply_filters( 'bbp_exclude_forum_ids', $retval, $forum_ids, $type );
}