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Bug #79373 uninitialized typed property cannot accessed in __get magic method
Submitted: 2020-03-12 16:56 UTC Modified: 2020-04-13 15:08 UTC
From: consatan at gmail dot com Assigned:
Status: Not a bug Package: Class/Object related
PHP Version: 7.4.3 OS: Linux
Private report: No CVE-ID: None
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 [2020-03-12 16:56 UTC] consatan at gmail dot com 
Description:
------------
A uninitialized typed property cannot accessed in __get method until unset() it. Test on 7.4.0~7.4.3, 7.4.0 is works.

Test script:
---------------
<?php
class Foo {
    public int $bar;
    
    public function __get($name) {
        if ('bar' === $name) {
            return $this->bar = 1;
        }
    }
}

$foo1 = new Foo();
var_dump($foo1);
var_dump($foo1->bar);

$foo2 = new Foo();
var_dump($foo2);
unset($foo2->bar);
var_dump($foo2);
var_dump($foo2->bar);

Expected result:
----------------
object(Foo)#1 (0) {
  ["bar"]=>
  uninitialized(int)
}
int(1)

object(Foo)#2 (0) {
  ["bar"]=>
  uninitialized(int)
}
object(Foo)#2 (0) {
  ["bar"]=>
  uninitialized(int)
}
int(1)

Actual result:
--------------
object(Foo)#1 (0) {
  ["bar"]=>
  uninitialized(int)
}

Warning: Uncaught Error: Typed property Foo::$bar must not be accessed before initialization in php shell code:1
Stack trace:
#0 {main}
  thrown in php shell code on line 1

object(Foo)#2 (0) {
  ["bar"]=>
  uninitialized(int)
}
object(Foo)#2 (0) {
  ["bar"]=>
  uninitialized(int)
}
int(1)

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 [2020-03-12 17:12 UTC] beberlei@php.net
-Status: Open +Status: Not a bug
 [2020-03-12 17:12 UTC] beberlei@php.net 
Your example seems to be wrong, you are not accessing Foo::$bar through __get, because its public. I assume its an error while making the example small and contained.

However the behavior here is correct regardless of __get or public access. You cannot access an uninitialized typed variable anywhere, before initializing it and this error represents that.
 [2020-04-13 14:47 UTC] ocramius@php.net 
Note: while this may or may not be interpreted as a bug, it is still a major BC break. In practice, a PHP 7.4.0 -> 7.4.1 upgrade requires changes in how type properties (public or private) are being shadowed for lazy-loading purposes.
 [2020-04-13 15:08 UTC] requinix@php.net 
> Note: while this may or may not be interpreted as a bug, it is still a major BC break. In practice, a
> PHP 7.4.0 -> 7.4.1 upgrade requires changes in how type properties (public or private) are being
> shadowed for lazy-loading purposes.
And in an ideal world the behavior seen in 7.4.0 would not have made it to the release. But it did. And it was incorrect: initialized and accessible are two different and separate concepts. And __get/etc. are about accessibility.

Better to fix the bug immediately and break the early adopters than to let it live until 7.5/8.0 where it would create even larger problems.
 
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