public function DeductUnits(BuildGroup $bg)
{
Helper::containsNegative($bg->Members());
// You can't deduct negative units, of course
if (!($this->Type() === $bg->Type() || $bg->Type() === "EMPTY" || $this->Type() === "EMPTY")) {
throw new Exception("You can't combine different types of BuildGroups!");
}
$otherList =& $bg->Members();
foreach ($this->Members() as $index => $buildItem) {
if (isset($otherList[$index])) {
$buildItem->Amount($buildItem->Amount() - $otherList[$index]->Amount());
}
}
Helper::containsNegative($this->Members());
// You can't deduct more than is present, of course
}