如何找出PHP對象數組的差值？

《深入PHP 物件導向、模式與實踐》的159頁有下面的代碼。
這兒是示範組合模式，removeUnit那個方法裡用到了array_udiff函數。作者的本意是這樣可以從 $units 屬性裡去除$unit 對象。我試了發現不起作用，關鍵就在$units參數裡存的是對象，對象做比較時不能排序，所以就失敗了。大家有沒有好的方法可以從數組裡排除掉一個對象嗎？


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);

回複內容：

《深入PHP 物件導向、模式與實踐》的159頁有下面的代碼。
這兒是示範組合模式，removeUnit那個方法裡用到了array_udiff函數。作者的本意是這樣可以從 $units 屬性裡去除$unit 對象。我試了發現不起作用，關鍵就在$units參數裡存的是對象，對象做比較時不能排序，所以就失敗了。大家有沒有好的方法可以從數組裡排除掉一個對象嗎？


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);

直接迴圈和unset解決了。

foreach($this->units as $k => $u){          if($u === $unit){             unset($this->units[$k]);         }     }

