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Posted : Friday, 03 February 2012, 19:35 | Permalink | Mark Here

JL235

WW Entries : 7

due to the way PHP automatically makes top level variables globally accessible, it means the moment you import a script within a function, the script breaks with strange errors. I’m currently battling this in Wordpress! ----- PlayMyCode.com - build and play in your browser, Blog, Twitter.

Posted : Friday, 03 February 2012, 19:35 | Permalink | Mark Here

Stealth

I don't think PHP is to blame as much as the programmers. You could do what you describe in Javascript, but it's not the languages fault. The barrier to entry in PHP is so low that it breeds bad code. I'm not saying PHP is a great language, but it can be used in ways that produce decent code.

-----
Andrew // stealth
"Some people see things as they are and say why? I dream things that never were and say why not?" - Robert Kennedy

Posted : Saturday, 04 February 2012, 01:21 | Permalink | Mark Here

JL235

WW Entries : 7

Actually no, if you did the same in JavaScript, it would actually work. ----- PlayMyCode.com - build and play in your browser, Blog, Twitter.

Posted : Saturday, 04 February 2012, 02:49 | Permalink | Mark Here

JL235

WW Entries : 7

I thought I'd add a bit more clarification on the problem. I've also simplified the code a little to help remove any distractions.

The problem is that in PHP, global variables are ones explicitely stated to be global, or are defined outside any functions (at the upper most level of scope). It's that second rule which is the gotcha.

Wordpress defines some common globals which are used through out it, for example:

$wp = new WP();

function wordpressFun() {
    global $wp;
    $wp->doSomething();
}

-->

Here PHP automatically makes the outer $wp variable global, since it is outside a function, and so the wordpress functions can all access it.

However this breaks if you ever want to load Wordpress dynamically. This is because you'll often end up doing this from inside a function. For example:

function myCode() {
    include( 'wordpresss' )
}

-->

... which ends up becomming ...

function myCode() {
    $wp = new WP();
    
    function wordpressFun() {
        global $wp;
        $wp->doSomething();
    }
}

-->

Now $wp is defined inside a function, and so it's no longer automatically global. As a result, the 'wordpressFun' fails to alias it. As a result, there are now two $wp variables. The local one, which contains the 'WP' object, and the global one which contains null.

If you did the same in JavaScript, it would work:

function myCode() {
    var wp = new WP();
    
    function wordpressFun() {
        wp.doSomething();
    }
}

-->

Since functions can always alias variables outside them, regardless of if that is done at the top level scope or not.

If you remove the 'var', then JavaScript will also automatically make it a global variable, at any level of scope! PHP only does this at the top level.

The problem here is that PHP's approach is inconsistent. It does one thing when run at one level of scope, and something entirely different at any other. This is especially annoying since it's normal for scripts to get included within functions.

-----
PlayMyCode.com - build and play in your browser, Blog, Twitter.

Posted : Saturday, 04 February 2012, 07:18 | Permalink | Mark Here

HoboBen

WW Entries : 9

I don't know if you want a work-around or just to moan at PHP (which is a totally normal thing to do!) but one idea would be a global associative array.

The Wordpress file:

global $wplocal = array();

$wp = new WP();
$foo = foo();
$bar = bar();

/* this saves on typing array('foo' => foo, ...),
   but is overkill for just one or two globals. */

$local_vars = array('wp', 'foo', 'bar');

foreach ($local_vars as $value) {
    $wplocal[$value] = $$value;
}


function wordpressFun1() {
    global $wplocal;
    $local_vars = array('wp', 'foo', 'bar');

    foreach ($local_vars as $value) {
        $$value = $wplocal[$value];
    }


    $wp->doSomething($foo, $bar);
}

function wordpressFun2() {
    global $wplocal;
    $local_vars = array('wp', 'just_foo');

    foreach ($local_vars as $value) {
        $$value = $wplocal[$value];
    }


    $wp->doSomething($just_foo);
}

-->

Obviously that could be annoying to do to every script.

-----

github

Posted : Saturday, 04 February 2012, 07:24 | Permalink | Mark Here

HoboBen

WW Entries : 9

I found this in the php.net user-supplied comments

<?php
function &teleport($vars = null){
  static $toSave = array();
  if($vars){
    foreach($vars as $k=>&$v)
      $toSave[$k] = $v;
  }
  return($toSave);
}

function myFuncA(){
  extract(teleport(),EXTR_REFS);
  $a = array('a'=>1,'b'=>2);
  $b = "An arbitrary value of no consequence\n";
  teleport(array('a'=>$a,'b'=>$b));
}
function myFuncB(){
  extract(teleport(),EXTR_REFS);
  $b = "Now this is of Consequence\n";
  $c = "Another of Consequence\n";
  teleport(array('c'=>$c));
}
function myFuncC(){
  extract(teleport(),EXTR_REFS);
  // $a,$b,$c are now in current scope
  print_r(get_defined_vars());
  print_r($a);
  echo($b);
  echo($c);
}

myFuncA();
myFuncB();

myFuncC();
?>

-->

Might be useful. Also of note is using "extract" function to dump an associative array directly into the local symbol table, which simplifies what I suggested (although you probably won't want ALL of your globals dumped in that way).

-----

github

Posted : Saturday, 04 February 2012, 10:42 | Permalink | Mark Here

JL235

WW Entries : 7

You can just add:

global $wp, $foo, $bar;

-->
.. just before you include. So then your essentially adding the global declarations missing from Wordpress. Although it took about 3 to 4 hours of debugging for me to work that out!

But my rant above was more about the gotcha it's self, how variables are presumed to be global in one place and not in another. Especially to point out that it's not the same behaviour you get in other languages.

-----
PlayMyCode.com - build and play in your browser, Blog, Twitter.

Posted : Saturday, 04 February 2012, 10:50 | Permalink | Mark Here

HoboBen

WW Entries : 9

The only thing about adding the globals before you include is obviously you need to know what is in the script before you include it (breaking encapsulation). Unless reintroducing everything into global scope is OK, in which case, there's no problem. ----- github

Posted : Saturday, 04 February 2012, 11:29 | Permalink | Mark Here

JL235

WW Entries : 7

Agreed.

However when you include Wordpress, it'll run off and touch these global variables straight away inside of functions, and then crash (because of the global rant above). The bug occurres in Wordpress code. So you must resolve the issue before you include Wordpress core.

Pre-stating them as global does this without needing to edit Wordpress core, and it'll probably survive future updates.

-----
PlayMyCode.com - build and play in your browser, Blog, Twitter.

Posted : Saturday, 04 February 2012, 16:31 | Permalink | Mark Here

Stealth

The Wordpress developers should have realized this and wrote better code. PHP does some weird things but it should never be the blame for bad code. That's the developers fault. ----- Andrew // stealth "Some people see things as they are and say why? I dream things that never were and say why not?" - Robert Kennedy

Posted : Friday, 17 February 2012, 19:01 | Permalink | Mark Here

JL235

WW Entries : 7

I've been hit a second time by this!

On Play My Code we have that the Google bot tries to setup games for playing, and the JS crashes. So we just disable the setup code for web crawlers.

After the last release, this has mysteriously stopped working. Turns out the problem is because I moved the script loading into it's own function, to localize variables, so my internal variables don't clash with those in scripts.

One of those scripts uses a global variable, but it's not declared. So it breaks, with no warning!

-----
PlayMyCode.com - build and play in your browser, Blog, Twitter.