php中出现这种构造函数/析构函数行为的原因是什么

我在PHP 中运行一个简单的构造函数/析构函数程序

为什么输出以两行开始

创建了狗0
创建的狗1

什么时候应该是

创建了狗0
被摧毁的狗0

<?php
class dog{
    public $name;
    public function __construct($name){
        $this->name = $name;
        echo "created dog $name <br/>";
    }
    public function __destruct()
    {
        echo "destroyed dog $this->name <br/>";
    }
}
for($i = 0;$i<=2;$i++)
{
    $dog = new dog($i);
}

$dog = new dog("last");
?>

全输出

created dog 0 
created dog 1 
destroyed dog 0 
created dog 2 
destroyed dog 1 
created dog last 
destroyed dog 2 
destroyed dog last