bbp_untrash_topic( $topic_id )

function bbp_untrash_topic( $topic_id = 0 ) {
	$topic_id = bbp_get_topic_id( $topic_id );

	if ( empty( $topic_id ) || !bbp_is_topic( $topic_id ) )
		return false;

	do_action( 'bbp_untrash_topic', $topic_id );

	// Get the replies that were not previously trashed
	$pre_trashed_replies = get_post_meta( $topic_id, '_bbp_pre_trashed_replies', true );

	// There are replies to untrash
	if ( !empty( $pre_trashed_replies ) ) {

		// Maybe reverse the trashed replies array
		if ( is_array( $pre_trashed_replies ) )
			$pre_trashed_replies = array_reverse( $pre_trashed_replies );

		// Loop through replies
		foreach ( (array) $pre_trashed_replies as $reply ) {
			wp_untrash_post( $reply );
		}
	}
}