Passing an argument to callback function working on an array

Question

I'm using an external class (Zebra_cURL) to execute multiple HTTP GET requests. It worked in the following way:

$items = array(
    0=>array('url' => 'url0'),
    1=>array('url' => 'url1'),
    2=>array('url' => 'url2'),
    3=>array('url' => 'url3'),
);
$curl = new Zebra_cURL();
$curl->get(array_column($urls,'url'),'scan_item',$moreimfo);

function scan_item($result,$moreimfo){
    $items[$key]['size'] = strlen($result->body);
}

So my callback should fill up my $items array with more info for each url (in my case - size of the page). So there is a missing $key variable.

This class supports extra parameters in the callbacks ($moreimfo in my case). BUT as I understand the data passing to each callback will be always the same.

$result object containing the original url info ($result->info['url']). So I COULD use it to find needed array element. However this looks too inefficient in case the size of an array will be big enough.

I think that I should find how to pass an array member key information for EACH callback execution. Is it possible without modifying the original class?

"without modifying the original class" - i don't think so. But since it's "only" a hashtable lookup how big must the array become for this to become unbearable? — VolkerK
– VolkerK, Commented Oct 6, 2015 at 10:43
@VolkerK I don't know actually. I just think that strcmp on an array should be much slower than picking the right element by its known key. So maybe I should skip my dislike and use strcmp but I just feel jittery seeing the inefficiency of the code. — Vlada Katlinskaya
– Vlada Katlinskaya, Commented Oct 6, 2015 at 10:48
Why strcmp? If you use an array with a string as a key, the string get's hashed when accessing the array element and the access is blazingly fast. — tillz
– tillz, Commented Oct 6, 2015 at 10:51
Oh, I'm blind today.... thought the url was the key of the array. Nevermind ;-) But would it be possible to use the url as the key in $items instead of 0,1,2,3? — VolkerK
– VolkerK, Commented Oct 6, 2015 at 10:51
@VolkerK Hm... Didn't think about it! Thank you for an idea! — Vlada Katlinskaya
– Vlada Katlinskaya, Commented Oct 6, 2015 at 10:52

VolkerK · Accepted Answer · 2015-10-06 14:26:25Z

2

If you use the url as key in the $items array the solution could be something like

<?php
$items = [
  'url0'=>array('url' => 'url0'),
  'url1'=>array('url' => 'url1'),
  'url2'=>array('url' => 'url2'),
  'url3'=>array('url' => 'url3'),
];
$curl = new Zebra_cURL();
$curl->get(
    array_keys($items),
    function($result) use (&$items) {
        $key = $result->info['url'];
        $items[$key]['size'] = strlen($result->body);
    }
);

using an anymous function that "Imports" the $items array via reference.

answered Oct 6, 2015 at 14:26

VolkerK

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2 Comments

Vlada Katlinskaya Over a year ago

Never heard about function use syntax. Interesting!

Stefan Gabos Over a year ago

Never hear of function use neither! here's how I do it: github.com/stefangabos/Zebra_cURL/issues/15

tillz · Accepted Answer · 2015-10-06 10:48:39Z

While it doesn't solve the original problem of passing a reference to the according array element to the callback, the following should be very fast (as noted in the comments, PHP Arrays are implemented using a hashtable).

$items = array(
    0=>array('url' => 'url0'),
    1=>array('url' => 'url1'),
    2=>array('url' => 'url2'),
    3=>array('url' => 'url3'),
);

$lookup=array();
foreach($lookup as $k=>$v) {
    $lookup[$v['url']]=$k;
}

$curl = new Zebra_cURL();
$curl->get(array_column($urls,'url'),'scan_item',$moreimfo);

function scan_item($result,$moreimfo){
    global $lookup,$items;
    $items[$lookup[$result->info['url']]]['size'] = strlen($result->body);
}

Probably you may consider using an OOP-approach, with the callback as a method, then the global-izing of the arrays shouldn't be necessary if you use $this->anyMember

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