& and _ - a human explanation?

[LemonInflux]

Hello. I've been looking through the gallery and phpBB source code, to learn how it is constructed, and I've come across 2 things I haven't met before:

 

& and _

 

For example, in the gallery core, they have 2 functions, function &getStorage() and _shutdown().

 

What is the significance of & and _? I can't find a simple, understandable explanation

 

Thanks in advance,

 

Tom

[Gamic]

The "&" symbol is usually used when passing values to a method by reference (or passing values from a method by reference), rather than by value. Have a look at the manual to find out more about passing by reference.

 

The "__" is usually used to denote an automatic method. For example "__construct()" will be called when a new object is created from a class.

 

<?php
//some example code
class foo{
	private $message;

	public function __construct($pMessage="Hello World"){
		$this->setMessage($pMessage);
	}
	public function getMessage(){
		return $this->message;
	}
	public function setMessage($pVal){
		$this->message=$pVal;
	}
}
$br="<br />\n";

$test=new foo();//message will be "Hello World"
$bar=new foo("Goodbye World");//message will be "Goodbye World"
echo $test->getMessage().$br.$bar->getMessage().$br;

$bar=&$test;//$bar now points to the same object as $test.
$test->setMessage("The Corn!");
echo $bar->getMessage();//should outuput "The Corn!"
?>

 

Output:
C:\xampp\php>php example.php
Hello World<br />
Goodbye World<br />
The Corn!
C:\xampp\php>

[LemonInflux]

I understand now! Thanks!

 

So if I had, in my class:

 

function _say($text="blah")
{
echo $text;
}

 

then if I said $foo = new foo(); (if the class is called foo), it would echo "blah" unless I had defined $text as something else, regardless of whether I call the function or not?

[Gamic]

There is a list of automatic functions, or magic methods. The two common ones are __construct and __desctruct.

 

in your case it would echo blah if you called the _say function, and only if you called the _say function as _say is not an automatic function that php will recognize as a magic method.

 

Have a read of this entry in the manual to learn more about magic methods.

[Daniel0]

The "__" is usually used to denote an automatic method. For example "__construct()" will be called when a new object is created from a class.

 

What LemonInflux asked about was a method called _shutdown() (1 underscore). When you're prepending class properties or methods with a single underscore it's signifying that the member is to be considered private or protected. This is a convention used for pre-PHP5 scripts as versions before that did not support member visibility. The ones with two underscores are called magic methods.