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Date: Mon, 28 Jan 2008 13:20:56 +0000
Reply-To: robin@soal.org
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Subject: [PHP-DEV] Protected static props redeclared as public share value across classes
From: rewbs.soal@gmail.com ("Robin Fernandes")

Hi all,

If a protected static property is overridden by a public static
property, both properties share the same value:

<?php
class A {
      protected static $a;
      public static function test() {
              A::$a = 'A::$a';
              echo A::$a . "\n";  // Prints 'A::$a'
              echo B::$a . "\n";  // Also prints 'A::$a', because
A::$a and B::$a share values.
      }
}

class B extends A {
      public static $a = 'B::$a';
}

A::test();
?>

This behaviour feels strange to me, because:

1. It only applies to that specific combination of visibility
modifiers. If you change A::$a to public OR B::$a to protected, then
A::$a and B::$a are treated as two separate entities. See
pastebin.com/fca2cd5b and pastebin.com/f4f94b32d .

2. It is inconsistent with the behaviour of static methods. See:
pastebin.com/f27f009c4 .

3. It differs from the behaviours of C#, Java and C++ (whereas, in
most other respects, PHP and these languages share a lot of common
ground regarding the concepts of visibility & static-ness). See:
http://pastebin.ca/871576, http://pastebin.ca/871975 and
http://pastebin.ca/871583.

The code for this behaviour was added to zend_compile.c in rev 1.474
(back in sept 2003 :). If I change it to ensure that protected A::$a
and public B::$a are treated as separate entities (quick patch against
5.2 snap here: pastebin.com/f7f175924 ), the only tests that fail are
those specifically designed to check for this behaviour:
Zend/tests/errmsg_024.phpt and
ext/reflection/tests/static_properties_002.phpt.


Is this a bug? If not, could you help me understand the decision to go
with this inheritance rule?

Many thanks!
Robin