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Subject: Re: Class constants on object references have variable-inconsistent
 accessibility
From: ajf@ajf.me (Andrea Faulds)

Hi Jakub,

Jakub Kubíček wrote:
> I have encountered an inconsistence, or rather a bug, in PHP's syntax.
> The thing is, in PHP you can access constants defined on a
> class using reference to an instance of this class, stored in
> variable. So we have a code:
>
> <?php
>
> class B {
>      const C = 4;
> }
>
> $b = new B;
> var_dump($b::C === B::C); // bool(true)
>
> ?>
>
> Which will nicely pass. But things will go wrong having a code trying
> to access the same constant on an object of B stored in member
> variable of class A -- let's see below:
>
> <?php
>
> class A {
>      /** @var B */
>      public $b;
> }
>
> $a = new A;
> $a->b = new B;
> var_dump($a->b::C === B::C); // Parse error: syntax error, unexpected
> '::' (T_PAAMAYIM_NEKUDOTAYIM) in...
>
> ?>
>
> Let me conclude that if there's access to class' constant using a
> reference to an instance of the class, it should be possible with any
> type of value-holder (so-called variable).
>

Which versions of PHP have you tried? The following works in PHP 7:

<?php

class B {
      const C = 4;
}

class A {
     /** @var B */
     public $b;
}

$a = new A;
$a->b = new B;
var_dump($a->b::C === B::C);

?>

It outputs:

bool(true)

PHP 7 dealt with a lot of issues like these with the Uniform Variable 
Syntax RFC:

https://wiki.php.net/rfc/uniform_variable_syntax

Unfortunately, if you want that code to work, you'll have to upgrade to 
PHP 7, because there's no plans for another 5.x release, and this isn't 
a simple bug fix.

Thanks.

-- 
Andrea Faulds
https://ajf.me/