PHP setting property that doesn't exist in class works, why? how?

Question

<?php

class ser {

    public $a;

}

$x = new ser;
$x->b = 10;

var_dump($x);

Something like this.

Class ser has only $a property, but we can set $b to new object of this class and it works despite this class doesn't have any $b property

output

E:\XAMPP\htdocs\fun\test2.php:12:
object(kurde)[1]
  public 'a' => null
  public 'b' => int 10

Why this works?

Why we can add property and set it to this class while it doesn't belong exactly to this class?

How is that possible and why is that possible?

Any purpose? Sense of making this possible?

Why is this allowed? Why we can do this? What is purpose of this and sense? @RiggsFolly — Krystian Polska
– Krystian Polska, Commented Aug 24, 2017 at 21:46
It's actually quite useful if you're in a framework and you want to pass some extra data with an object for which you might not have a property on that class. — Bram
– Bram, Commented Aug 24, 2017 at 21:55
@Bram if there is a framework, which is built around this behaviour, you probably should stay away from it. — tereško
– tereško, Commented Aug 24, 2017 at 21:56

Scopey · Accepted Answer · 2017-08-24 22:08:12Z

3

This is what PHP refers to as "overloading". This is different to overloading in almost any other object oriented language.

If you do not like it, you can use the __set magic method to throw an exception if a non-existent property is set:

public function __set($name, $value) {
    throw new \Exception('Property "'.$name.'" does not exist')
}

You can tell from the comments on the documentation what the general consensus of this "feature" is.

answered Aug 24, 2017 at 22:01

Scopey

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