PHP, does assignment use double memory for a variable?

Question

If I have a large object and assign another variable to that object, does php create two objects, or does it use a pointer internally?

for example:

<?php
$myObject = new Class_That_Will_Consume_Lots_Of_Memory();
$testObject = $myObject;

In this example will i be using 2 x the memory footprint of a Class_That_Will_Consume_Lots_Of_Memory instance or will it be 1 of those and a pointer?

http://www.php.net/manual/en/language.oop5.references.php – CBroe Jun 27 '13 at 11:01 — CBroe, Jun 27 '13 at 11:01

score 1 · Accepted Answer · edited May 23 '17 at 12:21

1

The latter: one object and a pointer/reference (and in fact, here, two pointers/references, since the first is one as well).

To get a new object, use clone.

Related: Are PHP5 objects passed by reference?

edited May 23 '17 at 12:21

Community

1
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answered Jun 27 '13 at 11:01

Denis de Bernardy

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@Cobra_Fast Yes, for things that are normally passed by value. Instance of objects, however, are passed by reference pretty much by definition. – Niet the Dark Absol Jun 27 '13 at 11:03
@Cobra_Fast: the & is not needed in php5. I believe it raises a warning or a strict notice, too. – Denis de Bernardy Jun 27 '13 at 11:06
@Cobra_Fast this was PHP4. … – bwoebi Jun 27 '13 at 11:14

score 0 · Answer 2 · answered Jun 27 '13 at 11:21

Objects in PHP5 are passed by reference, arrays and other types passing is based on Copy on Write technique:

$a = ['a'=>'b'];
$b = $a; // Here we used 1x memory
$b['x'] = 'y'; // Now it become 2x memory

You can use memory_get_usage() to debug memory usage.

PHP, does assignment use double memory for a variable?

2 Answers2