PHP autoload and static variable in function

Question

=== Base.php ===

<?php
class Base
{
    public static function e()
    {
        static $number = 0;
        $number++;
        var_dump($number);
    }
}

=== A.php ===

<?php
class A extends Base {}

=== B.php ===

<?php
class B extends Base {}

=== test.php ===

function __autoload($classname)
{
    require_once("{$classname}.php");
}

Base::e();
A::e();
B::e();

php test.php, result is:

int(1)
int(2)
int(2)

Why not result is 1,1,1?

It's ok if all class in one file. If one class in one file, it's error. — Jelly, Sep 09 '15 at 08:39
Is `__autoload` really important to reproduce this problem? Any difference if you import the classes manually? If it works the same without `__autoload`, you should take it out of the picture. Otherwise make more explicitly that this is only happening when using `__autoload`. — deceze, Sep 09 '15 at 13:10
PS: it *does* seem like autoloading is a crucial part of this. Using three `require_once` statements instead results in 1,1,1. — deceze, Sep 09 '15 at 13:18
My guess is that you are using opcache. And if you disable it, the problem will go away. — ircmaxell, Sep 09 '15 at 14:00
It is not enabled by default, it is a compile time option... — ircmaxell, Sep 09 '15 at 14:12

bwoebi · Answer 1 · 2015-09-09T14:18:09.910

6

Try

require "Base.php";
Base::e();
require "A.php";
A::e();

vs.

require "Base.php";
require "A.php";
Base::e();
A::e();

The former will yield int(1) int(2), while the latter yields int(1) int(1).

Why?

When a class is bound, the static variable content is copied at exactly that moment how it currently is. There is no backing up of the original value of the static variable.

That implies, when the static variable is 0 when class A is bound, A::e() will have 0 as static value; in case it's 1, A::e() will also have 1 as value.

Similar for B::e() then, as Base::e() and A::e() are independent as the values are copied (no references). It will also have the same static variable Base::e() has at the binding time of B.

edited Sep 09 '15 at 14:18

answered Sep 09 '15 at 14:08

bwoebi

23,637
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How does that explain how B returns 2 too? – Jonnix Sep 09 '15 at 14:11
@JonStirling B inherits from Base, not from A. – bwoebi Sep 09 '15 at 14:11
Ah yes, I think that makes sense. – Jonnix Sep 09 '15 at 14:13
What do you mean by that a class is bound? – Jelly Sep 17 '15 at 02:55
@Jelly The moment where the class is made available, internally (in source code) it's called class binding (early binding (immediately), delayed binding (what happens here), ...). Basically the merging of the class hierarchy in a class - and only after that you can use that class. – bwoebi Sep 17 '15 at 12:36

score 1 · Answer 2 · answered Sep 09 '15 at 13:34

I did some research on this problem and it is really weird.

Static properties inside methods remain their state between instances of object. Which may be confusing. Also there are two statics one is the static function and the other one is static variable inside method.

It may be connected with autoloader. I did similar example with your but without using static methods but using static variable inside method. The result is 1:1:1 using both autoloader and same file.

<?php
class Base
{
    public function t()
    {
        static $number = 0;
        $number++;
        var_dump($number);
    }

    public static function e()
    {
        static $number = 0;
        $number++;
        var_dump($number);
    }
}


$base = new Base();
$base->t();

$a = new A();
$a->t();

$b = new B();
$b->t();

Also if you won't execute Base::e() the result is correct.

I've did require_once without autoloading and it still works. So it is definitly because of autoloader.

If you put

require_once "Base.php";
require_once "A.php";
require_once "B.php";

instead of autoloader function it works. Why is that I have no idea I've tried to find anything considering static variables with autoloader but without success. However, this answer may give you some clue.

I answer two times this question, both wrongly. I'm still unaware of why spliting the files (now we know it's related with the Autoloader) affect the result. TRULY CLUELESS — Joako-stackoverflow, Sep 09 '15 at 13:56
Could be mate but, seems too basic and the impact it's to great to be an error. Could be if it's using a experimental branch of php, but it's unlikely. — Joako-stackoverflow, Sep 09 '15 at 14:00
@Joako-stackoverflow No, it's not a bug. PHP is just not backing up the initial value of the static variable (see my answer). — bwoebi, Sep 09 '15 at 14:10

PHP autoload and static variable in function

2 Answers2

Why?