How to pass parameters by reference to a function in PHP?

In PHP, passing parameters by reference to a function means that instead of passing a copy of the variable’s value to the function, you’re passing the actual variable itself. This allows the function to modify the original variable. This is done by prefixing the parameter with an ampersand (&) in the function definition.

Here is the technical description and examples of how to pass parameters by reference in PHP:

Technical Description
When a function argument is passed by reference, any changes made to the parameter within the function will affect the variable that was passed in from the calling context. In PHP, this is accomplished using the ampersand (&) symbol before the parameter name in the function definition.

Syntax
```
function functionName(&$parameter) { // function body
}
```

Example
Below is an example demonstrating passing a parameter by reference:

```
function addFive(&$num) { $num += 5;
}

$number = 10;
echo “Before function call: $number\n”; // Outputs: 10

addFive($number);
echo “After function call: $number\n”; // Outputs: 15
?>
```

In the above example:
1. We define a function `addFive` that expects a parameter to be passed by reference (indicated by the `&`).
2. We then call this function with the variable `$number`.
3. Inside the function, `$num` is a reference to `$number` in the calling scope. Thus, changes to `$num` affect `$number`.

If you don’t pass the variable by reference, the original value won’t be altered:

```
function addFive($num) { $num += 5;
}

$number = 10;
echo “Before function call: $number\n”; // Outputs: 10

addFive($number);
echo “After function call: $number\n”; // Outputs: 10
?>
```

Practical Uses
1. Swapping Values: Functions that need to swap the values of two variables can benefit from passing by reference.

\`\`\`php \`\`\`

1. Modifying Arrays: This is particularly useful when dealing with large arrays or objects where copying them would be resource-intensive.

\`\`\`php 1 [1] => 2 [2] => 3 [3] => 4 ) ?> \`\`\`

Notes
- Use references sparingly as they can make code harder to read and debug.
- Be mindful of unintended side effects, since changes to the reference will affect the original variable in the calling scope.

Sources
- [PHP Manual: Passing by Reference](https://www.php.net/manual/en/language.references.pass.php)
- [W3Schools: PHP Function Arguments](https://www.w3schools.com/php/php_functions.asp)
- [TutorialsPoint: PHP Functions](https://www.tutorialspoint.com/php/php_functions.htm)

These sources provide comprehensive information on PHP functions, including how to pass parameters by reference, offering further examples and detailed explanations.