php设计模式（组合模式2）

//组合模式改进
abstract class Unit{
    function getComposite(){
        return null;
    }
    abstract function bombardStrength();
}
abstract class CompositeUnit extends Unit{
    protected $units = array();
    public function getComposite(){
        return $this;
    }
    protected function units(){
        return $this->units;
    }
    public function removeUnit(Unit $unit){
        $this->units = array_udiff($this->units,array($unit),function($a, $b){
            if ($a===$b)
            {
                return 0;
            }
            return ($a>$b)?1:-1;
        });
    }
    public function addUnit( Unit $unit){
        if(in_array($unit, $this->units, true)){
            return;
        }
        $this->units[] = $unit;
    }
    public function bombardStrength()
    {
        $ret = 0;
        foreach($this->units as $unit){
            $ret += $unit->bombardStrength();
        }
        return $ret;
    }
}
//添加类这个类必须继承自composite；因为聚合工具类中要用到
class Army extends CompositeUnit{
    //public $units = [];

    public function bombardStrength()
    {
        $ret = 0;
        foreach($this->units as $unit){
            $ret += $unit->bombardStrength();
        }
        return $ret;
    }
}
//聚合工具类
class UnitScript{
    //代码解读  如果$occupyingUnit是抽象CompositeUnit的子类直接调用add
    static function joinExisting(Unit $unitNew, Unit $occupyingUnit ){
        $comm;
        if(!is_null($comm = $occupyingUnit->getComposite())){
            $comm->addUnit($unitNew);
        }else{
            //如果是unit的直接子类就实例化army类;
            $comm = new Army();
            $comm->addUnit($unitNew);
            $comm->addUnit($occupyingUnit);
        }
        return $comm;
    }
}
//被聚合对象
class B extends Unit{
    function bombardStrength(){
        return 2;
    }
}
//被聚合对象
class A extends Unit{
    function bombardStrength(){
        return 2;
    }
}
//如果穿进去的对象都是unit的子类，则需要实现army类，
echo UnitScript::joinExisting(new B, new A)->bombardStrength();