Note: Parent constructors are not called implicitly if the child class
defines a constructor. In order to run a parent constructor,a call to
parent::__construct() within the child constructor is required.

但是,如果子类不调用构造函数,父构造函数是否仍然被调用？还是应该创建一个调用父构造函数的构造函数？

IE：

class BaseClass {
   function __construct() {
       print "In BaseClass constructor\n";
   }
}

class SubClass extends BaseClass {
   function __construct() {
       parent::__construct();
   }
}