PHP的new self() 与new static()

参考链接：【PHP中new static()与new self()的区别异同分析】，【PHP中new self()和new static()的区别探究】，【PHP中static和self的区别】

要点其实是理解概念：

还是看看老外的专业解释吧：

self refers to the same class whose method the new operation takes place in.
译：self指那些方法被重写的类。tip：如果继承层次深（如继承深度大于1），当前子类没有重写父类方法，那么就需要找到最后一个方法被重写的类；如果是当前类重写的话，那当然就直接是当前类咯。

static in PHP 5.3's late static bindings refers to whatever class in the hierarchy which you call the method on.
译：static指当你所调用的方法所在的类。tip：其实这个就不用管继承了，永远都是当前类，不用管父类。

一、只有一层继承：

看代码：

class Father {

    public function getNewFather() {
        return new self();
    }

    public function getNewCaller() {
        return new static();
    }
}

class Sun1 extends Father {

}

class Sun2 extends Father {

}

$sun1 = new Sun1();
$sun2 = new Sun2();

print '$sun1->getNewFather():'.get_class($sun1->getNewFather());
echo '<br>';
print '$sun1->getNewCaller():'.get_class($sun1->getNewCaller());
echo '<br>';
print '$sun2->getNewFather():'.get_class($sun2->getNewFather());
echo '<br>';
print '$sun2->getNewCaller():'.get_class($sun2->getNewCaller());
echo '<br>';
echo '<br>';

结果：

$sun1->getNewFather():Father
$sun1->getNewCaller():Sun1
$sun2->getNewFather():Father
$sun2->getNewCaller():Sun2

二、有两层继承

看代码：

class Father {

    public function getNewFather() {
        return new self();
    }

    public function getNewCaller() {
        return new static();
    }
}

class Sun1 extends Father {
    public function getNewFather() {
        return new self();
    }

    public function getNewCaller() {
        return new static();
    }
}

class Sun2 extends Father {}

class subSun1 extends Sun1{}
class subSub2 extends Sun2{}

$sun1 = new Sun1();
$sun2 = new Sun2();

$subSun1=new subSun1();
$subSub2=new subSub2();

print '$sun1->getNewFather():'.get_class($sun1->getNewFather());
echo '<br>';
print '$sun1->getNewCaller():'.get_class($sun1->getNewCaller());
echo '<br>';
print '$sun2->getNewFather():'.get_class($sun2->getNewFather());
echo '<br>';
print '$sun2->getNewCaller():'.get_class($sun2->getNewCaller());
echo '<br>';
echo '<br>';

print '$subSun1->getNewFather():'.get_class($subSun1->getNewFather());
echo '<br>';
print '$subSun1->getNewCaller():'.get_class($subSun1->getNewCaller());
echo '<br>';
print '$subSun2->getNewFather():'.get_class($subSub2->getNewFather());
echo '<br>';
print '$subSun2->getNewCaller():'.get_class($subSub2->getNewCaller());

结果：

$sun1->getNewFather():Sun1
$sun1->getNewCaller():Sun1
$sun2->getNewFather():Father
$sun2->getNewCaller():Sun2

$subSun1->getNewFather():Sun1
$subSun1->getNewCaller():subSun1
$subSun2->getNewFather():Father
$subSun2->getNewCaller():subSub2