Question

It seems quite simple but I’m not getting it done for quite a while now…

class Main
{
    public $sub1;
    public $sub2;

    public function __construct()
    {
        $this->sub1 = new Sub1();
        $this->sub2 = new Sub2();
    }
}

class Sub1 extends Main
{
    public function __construct() {}

    public function helloWorld()
    {
        echo "hello world";
    }
}

class Sub2 extends Main
{
    public function __construct()
    {
        $this->sub1->helloWorld();
    }
}

new Main();

The result of the code is Fatal error: Call to a member function helloWorld(). But why? I don’t understand why the sub1 property of the Main class is NULL when I try to access it from sub2. Could anyone please explain it to me? Am I doing something basically wrong in terms of OOP programming? Am I hurting any concepts? Are there any better solutions?

Best regards!

Answer 1

You are overriding Main’s __construct() in both Sub1 and Sub2, meaning Main’s construct is never called. Even if you were to call parent::__construct() in Sub1 and Sub2’s construct, you would get an infinite loop because Main’s construct is initializing both subs.

Edit: Since you want to share objects, here are a couple SO questions that can help:
Sharing objects between PHP classes
How to create an object in a parent class shared by its children classes?