How to pass reference parameters PHP?

In PHP, you can pass parameters by reference using the & symbol before the parameter name in the function definition. This allows the function to modify the original variable instead of working with a copy.

Syntax

To pass a parameter by reference, prefix the parameter with & in the function definition ?

function functionName(&$parameter) {
    // Modify the original variable
}

Example

Here's how to pass a reference parameter to modify the original variable ?

<?php
function referenceDemo(&$number){
    $number = $number + 100;
    return $number;
}

$number = 900;
echo "The actual value is = " . $number . "<br>";
$result = referenceDemo($number);
echo "The modified value is = " . $result . "<br>";
echo "Original variable now = " . $number;
?>

The actual value is = 900
The modified value is = 1000
Original variable now = 1000

Pass by Value vs Pass by Reference

Compare the difference between passing by value and by reference ?

<?php
// Pass by value
function byValue($num) {
    $num = $num * 2;
    return $num;
}

// Pass by reference  
function byReference(&$num) {
    $num = $num * 2;
    return $num;
}

$value1 = 10;
$value2 = 10;

echo "Before: value1 = $value1, value2 = $value2<br>";

byValue($value1);
byReference($value2);

echo "After: value1 = $value1, value2 = $value2<br>";
?>

Before: value1 = 10, value2 = 10
After: value1 = 10, value2 = 20

Conclusion

Pass by reference using & allows functions to modify original variables directly. This is useful when you need to update the caller's variable or work with large data structures efficiently.