Property is suddenly undefined

[greew]

Bug report

I have class A which I can change, and class B which I don't have control over.

The output is this:

 ------ -----------------------------------------------
  Line   phpstan.php
 ------ -----------------------------------------------
  10     Dumped type: string
  12     Dumped type: mixed
  14     Access to an undefined property object::$foo.
 ------ -----------------------------------------------

I don't understand 2 things:

1. Why the type of $this->foo is changed to mixed
2. Why then $this->foo is suddenly undefined?

Code snippet that reproduces the problem

https://phpstan.org/r/40d3135d-7d52-4ebe-bb1c-7f23b4ecb4f4

Expected output

 ------ -----------------------------------------------
  Line   phpstan.php
 ------ -----------------------------------------------
  10     Dumped type: string
  12     Dumped type: string
 ------ -----------------------------------------------

Did PHPStan help you today? Did it make you happy in any way?

Still love the tool!!

[RobertMe]

Why the type of $this->foo is changed to mixed

Opening the Try link it's dumping mixed twice for me.

Why then $this->foo is suddenly undefined?

I presume because the foo(&$var) is by reference. So anything can happen with $var which due to the by reference means anything can happen to $this as well.
See also this version where I added a dumpType($this);: https://phpstan.org/r/d1c0c822-d92e-4af2-9cd7-195d46dbc57c As you can see it dumps mixed, as anything could have happened to it.

[ondrejmirtes]

Interesting behaviour! Passing $this into a function by reference does not do anything: https://3v4l.org/E5oPQ

But passing a different variable changes it: https://3v4l.org/XMTjK

PHPStan should reflect this.

[RobertMe]

What's more interesting is that it's any other variable , even a renamed $this: https://3v4l.org/3rASP

The reasoning is most likely backwards compatibility with PHP 4. As in PHP 4 class instances were value types (instead of reference types) so had to be passed by reference so the callee could/would actually modify the state of the object (also in the call site and not just in the called functions scope).

[RobertMe]

Seems like PHP just ignores the by reference directive when the "source" is $this. Also when assigning $this in a local assignment (and then reassigning the "destination"): https://3v4l.org/J1j0K

[greew]

Well, if you try and assign something to $this, it fails: https://3v4l.org/O6KAs - so yes, maybe $this ought to have some special meaning regarding references.

[greew]

It looks like the reference is broken if you try and change the $this value: https://3v4l.org/W17AG

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.