bbp_update_forum_id( int $post_id, int $forum_id )

function bbp_update_forum_id( $post_id, $forum_id ) {

	// Allow the forum ID to be updated 'just in time' before save
	$forum_id = apply_filters( 'bbp_update_forum_id', $forum_id, $post_id );

	// Update the post meta forum ID
	update_post_meta( $post_id, '_bbp_forum_id', (int) $forum_id );
}