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Bug #39713 Static variables defined in static methods duplicated in derived classes
Submitted: 2006-12-02 04:24 UTC Modified: 2006-12-03 00:47 UTC
From: paul at digitalbacon dot us Assigned:
Status: Not a bug Package: Scripting Engine problem
PHP Version: 5.2.0 OS: Linux, Mac OS X 10.4, Windows XP
Private report: No CVE-ID: None
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 [2006-12-02 04:24 UTC] paul at digitalbacon dot us
Description:
------------
When using a static variable defined inside a parent class's 
static method block, different outcomes can occur depending on  
the scope name used when calling.

The effect is that a non-overridden method in the child class 
is allocated a completely separate static variable... not how 
it works in C or C++, which I know PHP is not.

I encountered this problem implementing a singleton pattern in 
a parent class. I apologize for the reproduction code, but it 
does illustrate my perceived problem.

The closest bugs I found, relate to static class attributes, 
not regular static variables.

Reproduce code:
---------------
<?php

class TheParent {
        public static function staticMethod()
        {
                static $theStaticValue = true;

                if ($theStaticValue == true) {
                        $theStaticValue = false;
                        return true;
                } else return $theStaticValue; // false
       }
}

class TheChild extends TheParent {}

$a1 = TheParent::staticMethod();
$a2 = TheParent::staticMethod();
$b1 = TheChild::staticMethod();
$b2 = TheChild::staticMethod();

echo '$a1: ', $a1, "\n"; // true
echo '$a2: ', $a2, "\n"; // false
echo '$b1: ', $b1, "\n"; // true (I believe this should be false)
echo '$b2: ', $b2, "\n"; // false
?>

Expected result:
----------------
My intuition tells me that the parent's static variable should 
be used regardless of the scope name used... unless it's 
actually redefined in the child class.

In this example, I expect the output to be:

$a1: 1
$a2: 
$b1: 
$b2: 

Is local static method data not shared?

Actual result:
--------------
$a1: 1
$a2: 
$b1: 1
$b2: 

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 [2006-12-02 11:49 UTC] tony2001@php.net
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php


 [2006-12-03 00:47 UTC] paul at digitalbacon dot us
From the manual:

...A static variable exists only in a local function scope, 
but it does not lose its value when program execution leaves 
this scope.

I don't see why the use of the scope resolution operator 
(::) should change a static method's local function scope. 
Can a single static method really have multiple local scopes 
if using inheritance?
 
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