isset() on hooks doesn't respect backing value

[damek24]

Description

The following code:

<?php

class User {
	public ?string $id {
		get => $this->id; // get => $this->id ?? null; works
		set => $this->id = $value;
	}
}

class User2 {
    public string $id;
}

$u = new User();
$u2 = new User2();
var_dump(isset($u2->id));//false OK
var_dump(isset($u->id));//error

Resulted in this output:
First var_dump retuns false and this is ok, second - produces Fatal error: Uncaught Error: Typed property User::$id must not be accessed before initialization
But I expected this output instead:
false two times

This suggests that isset() on hooked properties may incorrectly trigger property access instead of checking initialization state, unlike regular typed properties.

PHP Version

PHP 8.5.0 (cli) (built: Nov 20 2025 19:17:11) (NTS)
Copyright (c) The PHP Group
Built by Debian
Zend Engine v4.5.0, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.0, Copyright (c), by Zend Technologies

PHP 8.4.15 (cli) (built: Nov 20 2025 17:43:25) (NTS)
Copyright (c) The PHP Group
Built by Debian
Zend Engine v4.4.15, Copyright (c) Zend Technologies
    with Zend OPcache v8.4.15, Copyright (c), by Zend Technologies
    with Xdebug v3.4.7, Copyright (c) 2002-2025, by Derick Rethans

Operating System

No response

[iluuu1994]

Hi @damek24. See:

• Properties (hooks) Other features that can be implemented in php 8.5 php-src#17436
• missing isset() on private(set) property (backing a get hook) php-src#18318

isset() intentionally calls get rather than checking the backing value of the property, because get might actually initialize the value. Code outside of the class it not meant to directly observe the backing value. The most reasonable way this can be resolved is by introducing an isset hook that can expose this information if desired.

But IMO the better approach is to simply not keep your properties uninitialized. You can initialize the property to null and then use a null-check at the call-site. Technically isset() works too. If null is a valid value, you can use some other sentinel like a single-case enum.

Anyway, if you'd like to see this happen, you're free to start a discussion on the mailing list and create an RFC:
https://wiki.php.net/rfc/howto

[damek24]

this case:

	public string $id {
		get => isset($this->id) ? $this->id : ''; 
		set => $this->id = $value;
	}

works

this case (normal type properties)

	public string $id;

works
but outside the isset outside class with proprty hooks throws fatal error which is weird

[iluuu1994]

Right, but think about what this is actually doing under the hood. https://3v4l.org/GfDG4#v8.5.0 The value isset() is checking is '', returned from get. That's the point of hooks, they hide the backing value behind an API. Imagine:

class Foo {
    public $expensive;

    public function __construct() {
        $this->expensive = expensive();
    }
}

I might want to refactor the property to become lazy, so that the computation of expensive() only happens when the property is actually accessed.

class Foo {
    public $expensive {
        get => $this->expensive ??= expensive();
    }
}

This change is meant to be invisible, but it isn't if isset() suddenly returns false. As mentioned, the best way to achieve this behavior is by introducing an isset hook, but that's a non-trivial change, requires an RFC, and still somewhat questionable, as IMO isset() on properties is an anti-pattern (because the properties should have been initialized in the first place).

[damek24]

I understand the reasoning from the language design perspective, but from a PHP user point of view this remains a surprising and undocumented behavior. I don’t plan to dig into PHP internals or propose an RFC. I only hope that future PHP versions will either address this or clearly document it as a known limitation.

[iluuu1994]

Fair enough. https://www.php.net/manual/en/language.oop5.property-hooks.php doesn't mention isset(), which it should.

[damek24]

Thanks for reopening this issue.
Having this behavior documented somewhere in the PHP documentation would be more than enough for me as a PHP user building my own framework.
Thanks in advance! 😍😎