PHP inheritance of abstract classes and overloading - php

Question

Say I have the following code, is there a way to somehow extend an abstract class on a child and require a different type of argument in the "overloaded" function. I want to insert various types of objects in the Collection through the add function. In some cases, I'd like to insert an Error object, sometimes some other (XYZ) object, and let's say that all those objects extend the same abstract class called Parent.
I would appreciate if somebody could tell me if something like this is even possible, and if it is suggest some ways to accomplish this. Note that production server on which I intend to host the application runs on php 5.6.40.
Thank you in advance.
namespace App;
use App\Models\Parent;
abstract class Collection
{
protected $collection;
public function __construct()
{
$this->collection = array();
}
abstract public function add($key, Parent $item);
}
public class ErrorList extends Collection
{
public function __construct()
{
parent::__construct();
}
public function add($key, Error $item)
{
$this->collection[$key] = $item;
}
}
namespace App\Models;
abstract class Parent {}
public class Error extends Parent {}
public class XYZ extends Parent{}

Answer 1

Try this
abstract class Collection
{
protected $collection;
public function __construct()
{
$this->collection = array();
}
//no type hinting
abstract public function add($key, $item);
}
class ErrorList extends Collection
{
// this constructor doing nothing , it can be removed and
// parent constructor will still be called unlike java or any other
// OOP
public function __construct()
{
parent::__construct();
}
//no type hinting
public function add($key, $item)
{
//code
}
}

Answer 2

If you're extending a class or implementing an interface the signature must match. You can however implement type checking yourself and type hint in a docblock.
As a side note, public class is invalid syntax.
abstract class Collection
{
protected $collection;
public function __construct()
{
$this->collection = array();
}
abstract public function add($key, Parent $item);
}
class ErrorList extends Collection
{
public function __construct()
{
parent::__construct();
}
/**
* #param $key
* #param Parent|Error $item
*/
public function add($key, Parent $item)
{
if (!($item instanceof Error)) {
throw new \InvalidArgumentException('Unable to add object to error list: ' . get_class($item));
}
$this->collection[$key] = $item;
}
}