What does the & sign mean in PHP?

Question

I was trying to find this answer on Google but I guess the symbol & works as some operator, or is just not generally a searchable term for any reason.. anyhow. I saw this code snippet while learning how to create wordpress plugins, so I just need to know what the & means when it precedes a variable that holds a class object.

//Actions and Filters   
if (isset($dl_pluginSeries)) {
    //Actions
    add_action('wp_head', array(&$dl_pluginSeries, 'addHeaderCode'), 1);
    //Filters
    add_filter('the_content', array(&$dl_pluginSeries, 'addContent')); 
}

Answer 1

This passes something by reference instead of value.

See:

http://php.net/manual/en/language.references.php
http://php.net/manual/en/language.references.pass.php

Answer 2

The ampersand preceding a variable represents a reference to the original, instead of a copy or just the value.

See here: http://www.phpreferencebook.com/samples/php-pass-by-reference/

Answer 3

weird to see this asked, since I learned about this few days ago. What I used it for was sending a variable to a function, have the function change the variable around. After the function is done, I don't need to return the function to return value and set the new value to my variable.

Example function fixString(&$str) { $str = "World"; }

$str = "Hello"; fixString($str); echo $str; //Outputs World;

Code without the & function fixString($str) { $str = "World"; return $str; }

$str = "Hello"; $str = fixString($str); echo $str; //Outputs World;

Answer 4

This will force the variable to be passed by reference. Normally, a hard copy would be created for simple types. This can come handy for large strings (performance gain) or if you want to manipulate the variable without using the return statement, eg:

$a = 1;

function inc(&$input)
{
   $input++;
}

inc($a);

echo $a; // 2

Objects will be passed by reference automatically.

If you like to handle a copy over to a function, use

clone $object;

Then, the original object is not altered, eg:

$a = new Obj;
$a->prop = 1;
$b = clone $a;
$b->prop = 2; // $a->prop remains at 1