《深入PHP 面向对象、模式与实践》的159页有下面的代码。
这儿是演示组合模式，removeUnit那个方法里用到了array_udiff函数。作者的本意是这样可以从 $units 属性里去除$unit 对象。我试了发现不起作用，关键就在$units参数里存的是对象，对象做比较时不能排序，所以就失败了。大家有没有好的方法可以从数组里排除掉一个对象吗？


class Army extends Unit{

private $units = array(); function addUnit(Unit $unit){ if(in_array($unit, $this->units, true)){ return; } $this->units[] = $unit; } function removeUnit(Unit $unit){ $this->units = array_udiff($this->units, array($unit), function ($a, $b) { return ($a === $b) ? 0: 1;}); } function bombardStrength(){ $ret = 0; foreach($this->units as $unit){ $ret += $unit->bombardStrength(); } return $ret; }

}

$army = new Army;

$archer = new Archer(); //$archer->addUnit(new Archer); $army->addUnit($archer); $army->addUnit($archer); $army->addUnit(new Archer); $army->addUnit(new LaserCannonUnit);

$army2 = new Army(); $army2->addUnit(new Archer); $army2->addUnit($archer); $army2->addUnit($archer); $army2->removeUnit($archer); $army->addUnit($army2); $army->addUnit($army2); print_r($army); echo $army->bombardStrength()."\n"; $army->removeUnit($army2); $army->removeUnit($army2); $army->removeUnit($army2); $army->removeUnit($archer); echo $army->bombardStrength(); print_r($army);