php autoload variable class name

Question

Can anyone explain how this works:

${(int)!${0}=$variable->other['class']}::my_static_method();

in the answer of this stackoverflow question:

error when using variable class name and static method

JustOnUnderMillions · Accepted Answer · 2016-09-01T14:58:04.443

3

It does the same as:

${0}=$variable->other['class'];//value here lets say is 'myClass'
${0}::my_static_method();//here now is myClass::my_static_method(); called

Why is (int)! used? Because he just tricks around.

Result of print (int)!${0}=$variable->other['class']; is 0.

Because if anything is set here ${0}=$variable->other['class'],

print (bool)${0}=$variable->other['class']; will be true.

Then it will be negated via !, so it becomes false and with (int) finally 0.

And thats the name of the variable that was set before: ${0}.

But it is very bad practise to give an global variable just an number.

Normaly all variables MUST start with _ or A-Za-z.

Dont know why its droped as example, maybe to make fun of the people.

Dont use this at all!

Just to show how its not done ;) (working code)

error_reporting(0);
define(0x7F,' ..the crazy Girl');
define('§','at? ');
define('_',' Wh');
${'$#?!'} = ' Arrr!';
$♂ = Tom;
$♀ = Tina;
$c = get_defined_constants();
print  _  . § . $♂ .' '.  Just . ' ' .  Want . ' ' . To ." ". Lov€ ." ". $♀ . $c[127] . ${'$#?!'};
//result: What? Tom Just Want To Lov€ Tina ..the crazy Girl Arrr!

Feel free to get crazy. :-)

edited Sep 01 '16 at 14:58

answered Sep 01 '16 at 14:22

JustOnUnderMillions

3,741
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Thanks. It dawned on me as I read through this how it was working. – CapIsland Sep 01 '16 at 14:29
"Dont use this at all!" +1 just for that – Dezza Sep 01 '16 at 14:33
So this will also work in the same way: `${'a' . substr($a = $variable->other['class'], 0, 0)}::my_static_method();` – CapIsland Sep 01 '16 at 14:34
@Capsland Yes. You substring nothing so you become `a` again. Read this also: https://wiki.php.net/rfc/uniform_variable_syntax – JustOnUnderMillions Sep 01 '16 at 14:38
@CapIsland Mark that as answer if it was THE answer you need, thnx – JustOnUnderMillions Sep 01 '16 at 15:13

score 2 · Answer 2 · edited May 23 '17 at 10:33

Its a variable variable statement, creating a global variable name using the boolean statement result in the first ${ }

${
- Create a variable variable.
(int)
- Cast result of following statement to integer
!
- Not statement, invert boolean result.
${0}
- create a variable $0
- this would normally cause a parse error where a T_VARIABLE is expected instead of a T_LNUMBER
=
- set $0 variable.
$variable->other['class']
- this is an object variable, defined somewhere else, what it does or what it holds I do not know.
}
- End of the first variable variable name.
::
- Call a static method from the class name created by the boolean statement

So in Layman's terms, it could create the following statement:

$1::my_static_method();

Why a digit? Because the variable name is created by a boolean statement, that is either true or false, it is inverted and cast to an integer. And in PHP true and false equals 1 and 0.

So $1 on failure and $0 on success.

Overall, keep in mind that you are bypassing the PHP interpreter for syntax errors. While the feature of variable variables is intended to create dynamic variable names I do not believe they meant it to be abused like this as a result it could mean your code could break with newer versions of PHP. An example would be the answer of JustOnUnderMillions where the result in PHP 7 is What? Tom Just Want To Lov€ Tina Arrr!

Just saying, using variable variable statements is bad programming practice anyways.

Thanks. Nice explanation also. – CapIsland Sep 01 '16 at 14:30 — CapIsland, Sep 01 '16 at 14:30

php autoload variable class name

2 Answers2