Why is an extended ArrayObject faster than the original ArrayObject?

Question

First I found this object vs array, then I added an ArrayObject and extended ArrayObject to my code. The result is strange: The extended ArrayObject is close to the common ArrayObject in terms of computing time.

This is my test case, array vs object vs arrayobject vs extended arrayobject:

<pre><?

set_time_limit(0);
$times = 2000;

function profiling($tester, $desc)
{
    $start = microtime(true);
    $tester();
    echo "$desc: ",(microtime(true) - $start),"\n";
}

profiling(function()
{
    global $times;
    for ($i=0; $i<$times; $i++) {
        $z = array();
        for ($j=0; $j<$times; $j++) {
            $z['aaa'] = 'aaa';
            $z['bbb'] = 'bbb';
            $z['ccc'] = $z['aaa'].$z['bbb'];
        }
    }
}, 'use array');


profiling(function()
{
    global $times;
    for ($i=0; $i<$times; $i++) {
        $z = (object) null;
        for ($j=0; $j<$times; $j++) {
            $z->aaa = 'aaa';
            $z->bbb = 'bbb';
            $z->ccc = $z->aaa.$z->bbb;
        }
    }
}, 'use object');

profiling(function()
{
    global $times;
    for ($i=0; $i<$times; $i++) {
        $z = new ArrayObject();
        for ($j=0; $j<$times; $j++) {
            $z['aaa'] = 'aaa';
            $z['bbb'] = 'bbb';
            $z['ccc'] = $z['aaa'].$z['bbb'];
        }
    }
}, 'use arrayobject');

profiling(function()
{
    global $times;
    for ($i=0; $i<$times; $i++) {
        $z = new MyArray();
        for ($j=0; $j<$times; $j++) {
            $z['bbb'] = 'bbb';
            $z['ccc'] = $z['aaa'].$z['bbb'];
        }
    }
}, 'use extends arrayobject');

class MyArray extends  ArrayObject
{
    function __construct()
    {
        parent::__construct(array('aaa'=>'aaa'));
    }
}

echo 'phpversion '.phpversion();

On my pc, the output is

use array: 4.1052348613739
use object: 5.6103208065033
use arrayobject: 5.4503121376038
use extends arrayobject: 4.5252590179443
phpversion 5.3.25

The ranking is: array > extends arrayobject > arrayobject > object.

Why is the extends ArrayObject faster than ArrayObject and Object?

Answer 1

It is because your function using the extended array object is not setting $z['aaa'] 2000 times but your function using ArrayObject is.

if i add a version of the extended array object function which does set $z['aaa'] the result is more consistant:

profiling(function()
{
    global $times;
    for ($i=0; $i<$times; $i++) {
        $z = new MyArray();
        for ($j=0; $j<$times; $j++) {
            $z['bbb'] = 'bbb';
            $z['ccc'] = $z['aaa'].$z['bbb'];
        }
    }
}, 'use extends arrayobject (no aaa)');

/* added MyArray function with $z['aaa'] = 'aaa' added to the loop */
profiling(function()
{
    global $times;
    for ($i=0; $i<$times; $i++) {
        $z = new MyArray();
        for ($j=0; $j<$times; $j++) {
            $z['aaa'] = 'aaa';
            $z['bbb'] = 'bbb';
            $z['ccc'] = $z['aaa'].$z['bbb'];
        }
    }
}, 'use extends arrayobject (with aaa)');

output is as follows:

use array: 1.3838648796082
use object: 1.9023339748383
use arrayobject: 2.0339980125427
use extends arrayobject (no aaa): 1.6399688720703
use extends arrayobject (with aaa): 2.040415763855
phpversion 5.4.4-14+deb7u7

notice that the function using ArrayObject and the function using the extended ArrayObject with $z['aaa'] in the loop have much closer times.