PHP References

PHP reference are the symbol table aliases by means of which content of one variable can be access by different names. The explicitly defined referenced variable needs to be preceded by ampersand (&) symbol. The functionality of PHP references can be explained using the analogy of Window’s shortcut. PHP references can be defined in PHP programming in various ways.

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Methods to Create PHP References

Mostly used methods to create PHP references are discussed as below:

1. Using the Keyword ‘global’

In the method reference can be created using the keyword ‘global’ before the referenced variable. Declaring a reference as global variable adds the variable to $GLOBAL array and enable the user to access a global variable within the scope of the function. Basically there are two ways through which a PHP reference can be defined being declared as global variable such as:

function Function_name() {
global $globalVar;
}
OR
function Function_name() {
$globalVar =& $GLOBALS["globalVar"];
}

Example

The below code snippet is designed to demonstrate the different between the value for the same variable with respect to local scope and to global scope.

<?php function functionname() {
$inputvar = "within function scope";
echo '$inputvar in global scope: ' . $GLOBALS["inputvar"] . "\n";
echo '$inputvar in current scope: ' . $inputvar . "\n";
}
$inputvar = "Outside function scope";
$othervar= $GLOBALS["inputvar"]; //Creating inputvar in GLOBAL array
functionname();
echo '$othervar : ' . $othervar . "\n";
?>

Output

Othervar is the reference set for the inputvar from GLOBAL array. It is not bound to the inputvar variable defined in the local scope of the function.

2. Using $this Variable

‘$this’ variable is default reference to the object for the function, of which, $this variable is referred.

Example

The below code demonstrates the usage of $this variable to access value of any class property from the chosen class object.

<?php class Thisclass {
var $clsproperty = 300;
function classmethod() {
$this->clsproperty = 500; // $this is a reference to the object
}
}
$clsObject = new Thisclass();
$clsObject->classmethod();
echo "The displayed value is: ". $clsObject->clsproperty;
//display the value updated using $this property
?>

Output

The value of the clsproperty is displayed based on the value set by using $this variable.

3. Passing an Object

In PHP programming, any operation performed on a class object such as assign, return or pass, etc; the operation always is carried out with reference to the object instead of its copy.

The standard syntax to create PHP object reference is followed as below:

class ClassName {
//Body of the class
}
$classObj1 = new ClassName ();
$classObj2= $classObj1;

Here classObj2 object is referring to the same content contained in classObj1.

Example

The below code snippet is designed to create reference object for the actual object and access its properties.

<?php class Costume {
// Declaring the class properties
public $name;
public $color;
// Declaring the class methods
function set_name($name) {
$this->name = $name;
}
function get_name() {
return $this->name;
}
function set_color($color) {
$this->color = $color;
}
function get_color() {
return $this->color;
}
}
//Creating the object
$constume1 = new Costume();
$constume1->set_name('Superman');
$constume1->set_color('Blue and Red');
//Creating the object reference
$constume2=$constume1;
echo "Costume1 Name: " . $constume1->get_name();
echo "\n";
echo "Costume1 Color: " .  $constume1->get_color();
echo "\n";
echo "\n";
echo "Costume2 Name: " . $constume2->get_name();
echo "\n";
echo "Costume2 Color: " .  $constume2->get_color();
?>

Output

The reference object Costume2 refers to the same values as carried within the properties name and color of the actual object Costume1.

Different Operations of PHP Programming

In PHP programming different operations are carried out with PHP references. Some of the major operations are discussed in the below session:

1. Passing by Reference

In order to enable a function to modify a variable which is defined out of its scope, the value needs to pass to the function by its reference.

Example

The below code snippet changes the value of the variable defined out of the scope of the called function using the reference to the variable.

<?php function Afunction(&$input) //passing the input argument by reference
{
$input*=10;
}
$outVar=5;
echo "Before the function is called: ".$outVar;
echo "\n";
Afunction($outVar);
echo "After the function is called: ".$outVar;
?>

Output

The value of the variable outvar is changed by the function AFunction().

2. Returning References

This operation enables the calling function to find out the variable to which reference is to be bound. It is recommended to use only if there is any technical requirement, else it does not add to the performance of the program.

Example

The below code snippet is designed to pass the return value from a function parent function as reference to the defined class parent class.

<?php class parentclass {
public $parentvar = "I am set at parent class";
public function &parentfunction()
{
return $this->parentvar;
}
}
$parentobj = new parentclass;
$newvar = &$parentobj->parentfunction();
echo $newvar;
echo "\n";
$parentobj->parentvar= "I am set outside of the class";
echo $newvar;
?>

Output

3. Unsetting PHP Reference

User can break the binding between the variable and reference using the method unset().

Example

The below code snippet demonstrates the usage of the method unset() to unbound the referenced variable firstinput from secondinput.

<?php $firstinput = "I am first input";
$secondinput =& $firstinput;
echo "First input: ". $firstinput;
echo"\n";
echo "Second input: " . $secondinput;
unset($firstinput);
echo"\n";
echo"\n";
echo "After unsetting the reference: ";
echo"\n";
$firstinput = "I am set to second input";
echo"\n";
echo "First input: ". $firstinput;
echo"\n";
echo "Second input: " . $secondinput;
?>

Output

Conclusion

PHP references are important feature that is incorporated in PHP scripting. PHP references are not pointers as it can be described for ‘C’ which also occupy memory to create duplicate element. Rather PHP references are just different alias to refer the content from the actual variable. If copy of an object is required for an object in PHP, it can be done with the keyword ‘clone’.

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