Pass constructor arguments to inherited child class - php

Question

I'm struggling with this for a while now and since Google has tons of results on this issue i'm wondering what i'm doing wrong since none of the solutions seems to work for me.
I have two classes File and Image. I let the File class decide wether the input is an image or another type of file. When the file is an image i want to pass that file to the Image class to process it.
So far i have this
Class File{
public $file;
function __construct($input){
$this->file = $input;
}
public function getFileType(){
// determine filetype of $this->file
return 'image';
}
}
Class Image Extends File{
function __construct(){}
public function test(){
return $this->file;
}
}
$file = new File('file.jpg');
if($file->getFileType() == 'image'){
$image = new Image;
echo $image->test();
}
But this doesn't output anything. How can i access the value of the constructor argument of the parent class in the inherited class? Calling parent::__construct(); in the child constructor class (as mentioned here) gives me a missing argument warning and this one (call_user_func_array(array($this, 'parent::__construct'), $args); in the child constructor) also doesn't work.
What am i missing?

Answer 1

First you need to understand that $image and $file in your code are 2 different objects.
$image knows nothing about $file and vice versa.
With your code design the solution can be:
Class File {
public $file;
function __construct($input){
$this->file = $input;
}
public function getFileType(){
// determine filetype of $this->file
return 'image';
}
}
Class Image Extends File{
function __construct($input)
{
parent::__construct($input);
// after that you have `$this->file` set
}
public function test(){
return $this->file;
}
}
$file = new Image('file.jpg');
if ($file->getFileType() == 'image'){
echo $file->test();
}
But such approach is messy. You create object of class Image and after creation you make sure that it is really image. I suppose you need to use something like fabric pattern and generate object of proper kind in a File class.