Reference or copy?
in [General]
|
From: Robert Cummings on 23 Jul 2008 04:13 On Wed, 2008-07-23 at 10:07 +0200, Yeti wrote: > Hello everyone, > > Many of you may be familiar with references in PHP. Now i read > somewhere in the PHP manual that creating references can take longer > than copies. PHP5+ also seems to reference a bit different thant PHP4 > did. > Here is some working example code: > > <?php > class useless { > var $huge_array; > function __construct() { > $this->huge_array = array(); > for ($i = 0; $i < 1024; $i++) $this->huge_array[] = $GLOBALS; // > fill ze array with copies of $GLOBALS array > return true; > } > function useless() { > return $this->__construct(); > } > } > $time_start = microtime(true); > $test_obj = new useless(); > $time_end = microtime(true); > $time = $time_end - $time_start; > echo "It took {$time} seconds without using the reference operator.\r\n"; > unset($test_obj); > $time_start = microtime(true); > $test_obj =& new useless(); > $time_end = microtime(true); > $time = $time_end - $time_start; > echo "It took {$time} seconds using the reference > operator.\r\n########## with obj2 ############\r\n"; > $time_start = microtime(true); > $test_obj = new useless(); > $obj2 = $test_obj; > $time_end = microtime(true); > $time = $time_end - $time_start; > echo "It took {$time} seconds without using the reference operator.\r\n"; > unset($test_obj); > $time_start = microtime(true); > $test_obj =& new useless(); > $obj2 =& $test_obj; > $time_end = microtime(true); > $time = $time_end - $time_start; > echo "It took {$time} seconds using the reference operator.\r\n"; > ?> > > I tested the code in PHP 4.4.7 and in PHP 5.2.5 and the results were > pretty much the same. Using references speeds up the script! > Occasionally obj2-with-references took longer than all the others. But > i don't know if that's to be taken serious. > > Now if i do not need a copy, isn't it smarter to use references instead? > > I'm grateful for any ideas, thoughts or experiences In PHP4 if you don't need a copy then use a reference... it will be faster. In PHP5 you don't get a copy unless you explicitly clone the object. And so, in PHP5 assignment by value is faster than assignment by reference. However, there may be the odd time you really want a reference. PHP4 is dead though... so they say. Cheers, Rob. -- http://www.interjinn.com Application and Templating Framework for PHP
From: Ted Wood on 23 Jul 2008 04:19 The general rules of thumb are --> don't use references unless you actually *want* a reference. And don't use references for performance reasons. Under PHP 4, it's generally been recommended to use a reference operator when creating objects. $obj =& new Object(); PHP uses references internally until it's necessary to create a copy: $a = array(); $a = $b; // internally, $b is a reference to $a $b[] = "chocolate"; // at this point, a copy is made, and $b is modified So PHP waits until a copy is actually needed before it makes one. Explicitly making copies incurs overhead because of the concept of "reference counting". So again, don't use references for performance reasons. ~Ted On 23-Jul-08, at 1:07 AM, Yeti wrote: > Hello everyone, > > Many of you may be familiar with references in PHP. Now i read > somewhere in the PHP manual that creating references can take longer > than copies. PHP5+ also seems to reference a bit different thant PHP4 > did. > Here is some working example code: > > <?php > class useless { > var $huge_array; > function __construct() { > $this->huge_array = array(); > for ($i = 0; $i < 1024; $i++) $this->huge_array[] = $GLOBALS; // > fill ze array with copies of $GLOBALS array > return true; > } > function useless() { > return $this->__construct(); > } > } > $time_start = microtime(true); > $test_obj = new useless(); > $time_end = microtime(true); > $time = $time_end - $time_start; > echo "It took {$time} seconds without using the reference operator.\r > \n"; > unset($test_obj); > $time_start = microtime(true); > $test_obj =& new useless(); > $time_end = microtime(true); > $time = $time_end - $time_start; > echo "It took {$time} seconds using the reference > operator.\r\n########## with obj2 ############\r\n"; > $time_start = microtime(true); > $test_obj = new useless(); > $obj2 = $test_obj; > $time_end = microtime(true); > $time = $time_end - $time_start; > echo "It took {$time} seconds without using the reference operator.\r > \n"; > unset($test_obj); > $time_start = microtime(true); > $test_obj =& new useless(); > $obj2 =& $test_obj; > $time_end = microtime(true); > $time = $time_end - $time_start; > echo "It took {$time} seconds using the reference operator.\r\n"; > ?> > > I tested the code in PHP 4.4.7 and in PHP 5.2.5 and the results were > pretty much the same. Using references speeds up the script! > Occasionally obj2-with-references took longer than all the others. But > i don't know if that's to be taken serious. > > Now if i do not need a copy, isn't it smarter to use references > instead? > > I'm grateful for any ideas, thoughts or experiences > Yeti > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php >
From: Ted Wood on 23 Jul 2008 04:21 On 23-Jul-08, at 1:19 AM, Ted Wood wrote: > > So PHP waits until a copy is actually needed before it makes one. > Explicitly making copies incurs overhead because of the concept of > "reference counting". So again, don't use references for performance > reasons. That should've been: Explicitly making "references", not copies... ~Ted
From: Yeti on 23 Jul 2008 16:20 <?php # So if i want a copy in PHP, like: $a = $b; # In PHP5 $a would still be a reference as long as $b is not being changed?(!) # Such behaviour makes it extremely easy to write a speedy script without worrying about copy/reference issues! # Thanks to all of you, # Ernie ?>
From: Ted Wood on 23 Jul 2008 16:27 In both PHP 4 and PHP 5, this would be an internal reference: $a = $b; until $b is changed. The only exception is with Object handling under PHP 4, which had flawed reference handling. So, the rule remains -- don't use references for performance reasons -- use them if you need references. :-) ~Ted On 23-Jul-08, at 1:20 PM, Yeti wrote: > <?php > # So if i want a copy in PHP, like: > > $a = $b; > > # In PHP5 $a would still be a reference as long as $b is not being > changed?(!) > # Such behaviour makes it extremely easy to write a speedy script > without worrying about copy/reference issues! > > # Thanks to all of you, > # Ernie > ?> > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php >
|
Pages: 1 Prev: [PHP] Reference or copy? Next: Getting info from SVN commit with php |